638. Q.—Would any difficulty be experienced in keeping the trunnions tight in a high pressure oscillating engine?
A.—It is very doubtful whether the steam trunnions of a high pressure oscillating engine will continue long tight if the packing consists of hemp; and it appears preferable to introduce a brass ring, to embrace the pipe, cut spirally, with an overlap piece to cover the cut, and packed behind with hemp.
639. Q.—How is the packing of the trunnions usually effected?
A.—The packing of the trunnions, after being plaited as hard as possible, and cut to the length to form one turn round the pipe, is dipped into boiling tallow, and is then compressed in a mould, consisting of two concentric cylinders, with a gland forced down into the annular space by three to six screws in the case of large diameters, and one central screw in the case of small diameters. Unless the trunnion packings be well compressed, they will be likely to leak air, and it is, therefore, necessary to pay particular attention to this condition. It is also very important that the trunnions be accurately fitted into their brasses by scraping, so that there may not be the smallest amount of play left upon them; for if any upward motion is permitted, it will be impossible to prevent the trunnion packings from leaking.
DIRECT ACTING SCREW ENGINE.
640. Q.—Will you describe the configuration and construction of a direct acting screw engine?
A.—I will take as an example of this species of engine, the engine constructed by Messrs. John Bourne & Co., for the screw steamer Alma, a vessel of 500 tons burden. This engine is a single steeple engine laid on its side, and in its general features it resembles the engines of the Amphion already described, only that there is one cylinder instead of two. The cylinder is of 42 inches diameter and 42 inches stroke, and the vessel has been propelled by this single engine at the rate of fourteen miles an hour.
641. Q.—Is not a single engine liable to stick upon the centre so that it cannot be started or reversed with facility?
A.—A single engine is no doubt more liable to stick upon the centre than two engines, the cranks of which are set at right angles with one another; but numerous paddle vessels are plying successfully that are propelled by a single engine, and the screw offers still greater facility than paddles for such a mode of construction. In the screw engine referred to, as the cylinder is laid upon its side, there is no unbalanced weight to be lifted up every stroke, and the crank, whereby the screw shaft is turned round, consists of two discs with a heavy side intended to balance the momentum of the piston and its connections; but these counter-weights by their gravitation also prevent the connecting rod and crank from continuing in the same line when the engine is stopped, and in fact they place the crank in the most advantageous position for starting again when it has to be set on.
642. Q.—Will you explain the general arrangement of the parts of this engine?
A.—The cylinder lies on its side near one side of the vessel, and from the end of the cylinder two piston rods extend to a cross head sliding athwartships, in guides, near the other side of the vessel. To this cross head the connecting rod is attached, and one end of it partakes of the motion of the cross head or piston, while the other end is free to follow the revolution of the crank on the screw shaft.
643. Q.—What is the advantage of two discs entering into the composition of the crank instead of one?
A.—A double crank, such as two discs form with the crank pin, is a much steadier combination than would result if only one disc were employed with an over-hung pin. Then the friction on the neck of the shaft is made one half less by being divided between the two bearings, and the short prolongation of the shaft beyond the journal is convenient for the attachment of the eccentrics to work the valves.
644. Q.—Will you enumerate some of the principal dimensions of this engine?
A.—The bottom frame, on which also the condenser is cast, forms the base of the engine: on one end of it the cylinder is set; on the other end are the guides for the cross head, and in the middle are the bearings for the crank shaft. The part where the cylinder stands is two feet high above the engine platform, and the elevation to the centre of the guides or the centre of the shaft is 10 inches higher than this. The metal both of the side frames and bottom flange is 1-1/4 inch thick. The cylinder has flanges cast on its sides, upon which it rests on the bottom frame, and it is sunk between the sides of the frame so as to bring the centre of the cylinder in the same plane as the centre of the screw shaft. The opening left at the guides for the reception of the guide blocks is 6 inches deep, and the breadth of the bearing surface is 11 inches. The cover of the guides is 8 inches deep at the middle, and about half the depth at the ends, and holes are cored through the central web for two oil cups on each guide. The brass for each of the crank shaft bearings is cut into four pieces so that it may be tightened in the up and down direction by the bolts, which secure the plummer block cap, and tightened in the athwartship direction, which is the direction of the strain, by screwing up a wedge-formed plate against the side of the brass, a parallel plate being applied to the other side of the brass, which may be withdrawn to get out the wedge piece when the shaft requires to be lifted out of its place. The air pump is bolted to one side of the bottom frame, and a passage is cast on it conducting from the condenser to the air pump. In this passage the inlet and outlet valves at each end of the air pump are situated, and appropriate doors are formed above them to make them easily accessible. The outlet passage leading from the air pump communicates with the waste water pipe, through which the water expelled by the air pump is discharged overboard.
645. Q.—Is the cylinder of the usual strength and configuration?
A.—The cylinder is formed of cast iron in the usual way, and is 1-1/8 inch thick in the barrel. The ends are of the same thickness, but are each stiffened with six strong feathers. The piston is cast open. The bottom of it is 5/8ths of an inch thick, and it is stiffened by six feathers 3/4 of an inch thick; but the feather connecting the piston rod eyes is 1-1/4 inch thick, and the metal round the eyes is 2 inches thick. The piston is closed by a disc or cover 5/8ths of an inch thick, secured by 15 bolts, and this cover answers also the purpose of a junk ring. The piston packing consists of a single cast iron ring 3-1/2 inches broad, and 1/2 inch thick, packed behind with hemp. This ring is formed with a tongue piece, with an indented plate behind the cut; and the cut is oblique to prevent a ridge forming in the cylinder. The total thickness of the piston is 5-1/2 inches. The piston rods are formed with conical ends for fitting into the piston, but are coned the reverse way as in locomotives, and are secured in the piston by nuts on the ends of the rods, these nuts being provided with ratchets to prevent them from unscrewing accidentally.
646. Q.—What species of slide valve is employed?
A.—The ordinary three ported valve, and it is set on the top of the cylinder. The cylinder ports are 4-1/2 inches broad by 24 inches long; and to relieve the valve from the great friction due to the pressure on so large a surface, a balance piston is placed over the back of the valve, to which it is connected by a strong link; and the upward pressure on this piston being nearly the same as the downward pressure on the valve, it follows that the friction is extinguished, and the valve can be moved with great case with one hand. The balance piston is 21 inches in diameter. In the original construction of this balance piston two faults were committed. The passage communicating between the condenser and the top of the balance piston was too small, and the pins at the ends of the link connecting the valve and balance piston were formed with an inadequate amount of bearing surface. It followed from this misproportion that the balance piston, being adjusted to take off nearly the whole of the pressure, lifted the valve off the face at the beginning of each stroke. For the escape of the steam into the eduction passage momentarily impaired the vacuum subsisting there, and owing to the smallness of the passage leading to the space above the balance piston, the vacuum subsisting in that space could not be impaired with equal rapidity. The balance piston, therefore, rose by the upward pressure upon it momentarily predominating over the downward pressure on the valve; but this fault was corrected by enlarging the communicating passage between the top of the balance piston and the eduction pipe. The smallness of the pins at the ends of the link connecting the valve and balance piston, caused the surfaces to cut into one another, and to wear very rapidly, and the pins and eyes in this situation should be large in diameter, and as long as they can be got, as they are not so easily lubricated as the other bearings about the engine, and are moreover kept at a high temperature by the steam. The balance piston is packed in the same way as the main piston of the engine. Its cylinder, which is only a few inches in length, is set on the top of the valve casing, and a trunk projects upwards from its centre to enable the connecting link to rise up in it to attain the necessary length.
647. Q.—What is the diameter of the piston rods and connecting rod?
A.—The piston rods, which are two in number, are 3 inches diameter, and 12 feet 10 inches long over all. They were, however, found to be rather small, and have since been made half an inch thicker. The connecting rod consists of two rods, which are prolongations of the bolts that connect the sides of the brass bushes which encircle the crank pin and cross head. The connecting rod is shown in perspective in fig. 52. The rods composing it are each 2-3/4 inches in diameter.
648. Q.—Will you describe the configuration of the cross head.
A.—The cross head, exhibited in fig. 53, is a round piece of iron like a short shaft, with two unequal arms keyed upon it, the longer of which b works the air pump, and the shorter c works the feed pump. The piston rods enter these arms at a A. The cross head is 8 inches diameter where it is embraced by the connecting rod at e, and 7 inches diameter where the air pump and feed pump arms are fixed on. The ends of the cross head d d, for a length of 12 inches, are reduced to 3 inches diameter where they fit into round holes in the centre of the guide blocks. Those blocks are of cast iron 6 inches deep, 11 inches wide, and 14 inches long, and they are formed with flanges 1 inch thick on the inner sides of the blocks. The projection of the air pump lever from the centre of the cross head is 1 foot 9 inches, and it is bent 5-3/4 inches to one side to enable it to engage the air pump rod. The eye of this arm is 6 inches broad and about 2 inches thick. At the part where one of the piston rods passes through it, the arm is 8 inches deep and 6 inches wide; but the width thereafter narrows to 3 inches, and finally to 2 inches; and the depth of the web of the arm reduces from 8 inches at the piston rod, to 4 inches at the eye, which receives the end of the air pump rod. The feed pump arm is only 3 inches thick, and has 9 inches of projection from the centre of the cross head; but the eye attached to it on the opposite side of the cross head for the reception of the other piston rod is of the same length as that part of the air pump arm which one of the piston rods passes through. The piston rods have strong nuts on each side of each of these arms to attach them to the arms, and also to enable the length of the piston rods to be suitably adjusted, to leave equal clearance between the piston and each end of the cylinder at the termination of the stroke.
649. Q.—Will you recapitulate the main particulars of the air pump?
A.—The air pump is made of brass 12-1/2 inches diameter and 42 inches stroke, and the metal of the barrel is 9/16ths of an inch thick. The air pump bucket is a solid piston of brass, 6-1/2 inches deep at the edge, and 7 inches deep at the eye; and in the edge three grooves are turned to hold water which answers the purpose of packing. The inlet and outlet valves of the air pump consist of brass plates 1/2 inch with strong feathers across them, and in each plate there are six grated perforations covered by india rubber discs 7 inches in diameter. These six perforations afford collectively an area for the passage of the water equal to the area of the pump. The air pump rod is of brass, 2-1/2 inches diameter.
650. Q.—What are the constructive peculiarities of the discs and crank pin?
A.—The discs, which are 64 inches diameter, are formed of cast iron, and are 2-1/2 inches thick in the body, and 5 inches broad at the rim. The crank shaft is 8-1/2 inches diameter, and the central boss of the disc which receives the shaft measures 10 inches through the eye, and the metal of the eye is 3 inches thick. In the part of the disc opposite to the crank pin, the web is thickened to 10 inches for nearly the whole semicircle, with the view of making that side of the disc heavier than the other side; and when the engine is stopped, the gravitation of this heavy side raises the crank pin to the highest point it can attain, whereby it is placed in mid stroke, and cannot rest with the piston rods and connecting rod in a horizontal line. The crank pin is 8-1/2 inches diameter, and the length of the bearing or rubbing part of it is 16 inches. It is secured at the ends to the discs by flanges 18 inches diameter, and 2 inches thick. These flanges are indented into thickened parts of the discs, and are each attached to its corresponding disc by six bolts 2 inches diameter, countersunk in the back of the disc, and tapped into the malleable iron flange. Besides this attachment, each end of the pin, reduced to 4-1/2 inches diameter, passes through a hole in its corresponding disc, and the ends of the pin are then riveted over. The crank pin is perforated through the centre by a small hole about 3/4 of an inch in diameter, and three perforations proceed from this central hole to the surface of the pin. Each crank shaft bearing is similarly perforated, and pipes are cast in the discs connecting these perforations together. The result of this arrangement is, that a large part of the oil or water fed into the bearings of the shaft is driven by the centrifugal action of the discs to the surface of the crank pin, and in this way the crank pin may be oiled or cooled with water in a very effectual manner. To intercept the water or oil which the discs thus drive out by their centrifugal action, a light paddle box or splash board of thin sheet brass is made to cover the upper part of each of the discs, and an oil cup with depending wick is supported by the tops of these paddle boxes, which wick is touched at each revolution of the crank by a bridge standing in the middle of an oil cup attached to the crank pin. The oil is wiped from the wick by the projecting bridge at each revolution, and subsides into the cup from whence it proceeds to lubricate the crank pin bearing. This is the expedient commonly employed to oil the crank pins of direct acting engines; but in the engine now described, there are over and above this expedient, the communicating passages from the shaft bearings to the surface of the pin, by which means any amount of cooling or lubrication can be administered to the crank pin bearing, without the necessity of stopping or slowing the engine.
651. Q.—What is the diameter of the screw shaft?
A.—The screw shaft is 7-1/2 inches diameter, but the bearings on each side of the disc are 8-1/2 inches diameter, and 16 inches long. Between the side of the disc and the side of the contiguous bearings there is a short neck extending 4-3/4 inches in the length of the shaft, and hollowed out somewhat to permit the passage of the piston rod; for one piston rod passes immediately above the shaft on the one side of the discs, and the other piston rod passes immediately below the shaft on the other side of the discs. A short piece of one piston rod is shown in fig. 54.
652. Q.—How is the thrust of the screw shaft received?
A.—The thrust of the screw shaft is received upon 7 collars, each 1 inch thick, and with 1 inch of projection above the shaft. The plummer block for receiving the thrust of the shaft is shown in fig. 55, and the coupling to enable the screw propeller to be disconnected from the engine, so that it may revolve freely when the vessel is under sail, is shown in fig. 56. When it is required to disengage the propeller from the engine, the pins passing through the opposite eyes shown fig. 56, are withdrawn by means of screws provided for that purpose, and the propeller and the engine are thenceforth independent of one another.
653. Q.—Will you describe the arrangement of the valve gearing?
A.—The end of the screw shaft, after emerging from the bearing beside the disc, is reduced to a diameter of 4 inches, and is prolonged for 4-1/2 inches to give attachment to the cam or curved plate which gives motion to the expansion valve. This plate is 3-1/2 inches thick, and a stud 3-1/2 inches diameter is fixed in the plate at a distance of 5 inches from the centre of the shaft. To this stud an arm is attached which extends to a distance of 2 inches from the centre of the shaft in the opposite direction, and the end of this arm carries a pin of 2-1/2 inches diameter. From the pin most remote from the centre of the shaft, a rod 2-1/2 inches broad and 1 inch thick extends to the upper end of the link of the link motion; and from the pin least remote from the centre of the shaft, a similar rod extends to the lower end of the link of the link motion. This link, which is represented in fig. 57, is 2-1/4 inches broad, 1 inch thick, and is capable of being raised or lowered 25 inches in all. In the open part of the link is a brass block, which, by raising or lowering the link, takes either the position in which it is represented at the centre of the link, or a position at either end of it. Through the hole in the brass block a pin passes to attach the brass to the end of a lever fixed on the valve shaft; so that whatever motion is imparted to the brass block is communicated to the valve through the medium of this lever. If the brass block be set in the middle of the link, no motion is communicated to it, and the valve being consequently kept stationary and covering both ports, the engine stops. If the link be lowered until the brass block comes to the upper end of the link, the valve receives the motion of the eccentric for going ahead, and the engine moves ahead; whereas if the link be raised until the brass block comes to the lower end of the link, the valve receives the motion of the backing eccentric, and the engine moves astern. Instead of eccentrics, however, pins at the end of the shaft are employed in this engine, the arrangement partaking of the nature of a double crank; but the backing pin has less throw than the going ahead pin, whereby the efficient length of the link for going ahead is increased; and the operation of backing, which does not require to be performed at the highest rate of speed, is sufficiently accommodated by about half the throw being given to the valve that is given in going ahead. A valve shaft extends across the end of the cylinder with two levers standing up, which engage horizontal side rods extending from a small cross head on the end of the valve rod. A lever extends downwards from the end of the valve shaft, which is connected by a pin to the brass block within the link; and the link is moved up or down by the starting handle, which, by means of a spring bolt shooting into a quadrant, holds the starting handle at any position in which it may be set.
654. Q.—What is the diameter and pitch of the screw propeller?
A.—The diameter is 7 feet and the pitch 14 feet. The propeller is Holm's conchoidal propeller. Its diameter is smaller than is advisable, being limited by the draught of water of the vessel; and the vessel was required to have a small draught of water to go over a bar. This engine makes, under favorable circumstances, 100 strokes per minute. The speed of piston with this number of strokes is 700 feet per minute, and the engine works steadily at this speed, the shock and tremor arising from the arrested momentum of the moving parts being taken away by the counterbalance applied at the discs.
655. Q.—Will you describe the principal features of a modern locomotive engine?
A.—I will take for this purpose the locomotive Snake, constructed by John V. Gooch for the London and South Western Railway, as an example of a modern locomotive of good construction, adapted for the narrow gauge. The length of the wheel base of this engine is 12 feet 8-1/2 inches. There are two cylinders, each 14-1/4 inches diameter and 21 inches stroke. The total weight of the engine is 19 tons; and this weight is so distributed on the wheels as to throw 8 tons on the leading wheels, 6 tons on the driving wheels, and 5 tons on the hind wheels. The engine is made with outside cylinders, and the cylinders are raised somewhat out of the horizontal line to enable them better to clear the leading wheels.
656. Q.—What are the dimensions of the boiler?
A.—The interior of the fire box is 3 feet 7-1/4 inches wide by 3 feet 5-1/2 inches long, measuring in the direction of the rails. The area of the fire grate is consequently 12.4 square feet. The bars are somewhat lower on the side next the fire door than at the side next the tubes, and the mean height of the crown of the fire box above the bars is 3 feet 10 inches. The top edge of the fire door is about 7 inches lower than the crown of the fire box. The fire box is divided transversely by a corrugated feather or bridge of plate iron, containing water, about 3-1/2 inches wide, and of about one-third of the height of the fire box in the centre of the feather, and about two-thirds the height of the fire box at the sides where it joins the sides of the fire box. The internal shell of the fire box tapers somewhat upwards to facilitate the disengagement of the steam. It is about 2 inches narrower and shorter at the top than at the bottom; the water space between the external and internal shell of the fire box being 2 inches at the bottom and 3 inches at the top.
657. Q.—Of what material is the fire box composed?
A.—The external shell of the fire box is formed of iron plates 3/8ths of an inch thick, and the internal shell is formed of copper plates 1/4 inch thick, but the tube plate is 3/4 inch thick. The fire grate is rectangular, and the internal and external shells are tied together by iron stay bolts 3/4 inch diameter, and pitched about 4 inches apart. The roof of the fire box is stiffened by six strong bars extending from side to side of the fire box like beams, and the top of the fire box is secured to these bars, so that it cannot be forced down without breaking or bending them.
658. Q.—What are the dimensions of the barrel of the boiler?
A.—The barrel of the boiler is 3 feet 7-1/2 inches in diameter, and 10 feet long. It is formed of iron plates 3/8ths of an inch thick, riveted together. It is furnished with 181 brass tubes 1-7/8 inch diameter and 10 feet long, secured at the ends by ferules. The tube plate at the smoke box end is 5/8ths of an inch thick, and the tube plates above the tubes are tied together by eight iron rods 7/8ths of an inch thick, extending from end to end of the boiler. The metal of the tubes is somewhat thicker at the end next the fire, being 13 wire gauge at fire box end, and 14 wire gauge at smoke box end. The rivets of the boiler are 3/4 inch diameter and 1-1/2 inch pitch. The plating of the ash pan is 5/16ths of an inch thick, and the plating of the smoke box is 3/16ths of an inch thick.
659. Q.—Will you describe the structure of the framework on which the boiler and its attachments rest, and in which the wheels are set?
A.—The framework or framing consists of a rectangular structure of plate iron circumscribing the boiler, with projecting lugs or arms for the reception of the axles of the wheels. In this engine the sides of the rectangle are double, or, as far as regards the sides, there are virtually two framings, one for the reception of the driving axles, and the other for the reception of the axles not connected with the engine. The whole of the parts of the outer and inner framings are connected together by knees at the corners, and the double sides are elsewhere connected by intervening brackets and stays, so as to constitute the whole into one rigid structure. The whole of the plating of the inside frame is 3/4 inch thick and 9 inches deep. The plating of the outside frame is of the same thickness and depth at the fore part, until it reaches abaft the position of the cylinders and guides, where it reduces to 1/2 inch thick. The axle guard of the leading wheels is formed of 3/4 plate bolted to the frame with angle iron guides. The axle guards of the trailing wheels are formed of two 1/2 inch plates, with cast iron blocks between them to serve as guides. The ends of the rectangular frame are formed of plates 3/4 thick, and at the front end there is a buffer beam of oak 4-1/2 inches thick and 15 inches deep. The draw bolt is 2 inches diameter. There are two strong stays on each side, joining the barrel of the boiler to the inside framing, and one angle iron on each side joining the bottom of the smoke box to the inside framing.
660. Q.—Of what construction are the wheels?
A.—The wheels and axles are of wrought iron, and the tires of the wheels are of steel. The driving wheels are 6 feet 6-1/2 inches in diameter, and the diameter of crank pin is 3-1/2 inches. The diameter of the smaller wheels is 48-1/2 inches. The axle boxes are of cast iron with bushes of Fenton's metal, and the leading axle has four bearings. The springs are formed of steel plates, 3 feet long, 4 inches broad, and 12 inch thick. The axle of the driving wheel has two eccentrics, forged solid upon it, for working the pumps.
661. Q.—Will you specify the dimensions of the principal parts of the engine?
A.—Each of the cylinders which is 14-1/4 inches diameter, has the valve casing cast upon it. The steam ports are 13 inches long and 1-5/8 inches broad, and the exhaust port is 2-1/2 inches broad. The travel of the valve is 4-1/8 inches, the lap 1 inch, and the lead 1/4 inch. The piston is 4 inches thick: its body is formed of brass with a cover of cast iron, and between the body and the cover two flanges, forged on the piston rod, are introduced to communicate the push and pull of the piston to the rod. The piston rod is of iron, 2-1/2 inches diameter. The guide bars for guiding the top of the piston rod are of steel, 4 inches broad, fixed to rib iron bearers, with hard wood 1/4 of an inch thick, interposed. The connecting rod is 6 feet long between the centres, and is fitted with bushes of white metal. The eccentrics are formed of wrought iron, and have 4-1/8 inches of throw. The link of the link motion is formed of wrought iron. It is hung by a link from a pin attached to the framing; and instead of being susceptible of upward and downward motion, as in the case of the link represented in fig. 57 a rod connecting the valve rod with the movable block in the link, is susceptible of this motion, whereby the same result is arrived at as if the link were moved and the block was stationary. One or the other expedient is preferable, according to the general nature of the arrangements adopted. The slide valve is of brass, and the regulator consists of two brass slide valves worked over ports in a chest in the steam pipe, set in the smoke box. The steam pipe is of brass, No. 14. wire gauge, perforated within the boiler barrel with holes 1/12th of an inch in diameter along its upper side. The blast pipe, which is of copper, has an orifice of 4-1/4 inches diameter. There is a damper, formed like a Venetian blind, with the plates running athwartships at the end of the tubes.
662. Q.—Of what construction is the safety valve?
A.—There are two safety valves, consisting of pistons 1-3/16 inch in diameter, and which are kept down by spiral springs placed immediately over them. A section of this valve is given in fig. 58.
663. Q.—What are the dimensions of the feed pumps?
A.—The feed pumps are of brass, with plungers 4 inches diameter and 3-1/4 inches stroke. The feed pipe is of copper, 2 inches diameter. A good deal of trouble has been experienced in locomotives from the defective action of the feed pump, partly caused by the leakage of steam into the pumps, which prevented the water from entering them, and partly from the return of a large part of the water through the valves at the return stroke of the pump, in consequence of the valve lifting too high. The pet cock—a small cock communicating with the interior of the pump—will allow any steam to escape which gains admission, and the air which enters by the cock cools down the barrel of the pump, so that in a short time it will be in a condition to draw. The most ordinary species of valve in the feed pumps of locomotives, is the ball valve.
Notwithstanding the excellent performance of the best examples of locomotive engines, it is quite certain that there is still much room for improvement; and indeed various sources of economy are at present visible, which, if properly developed, would materially reduce the expense of the locomotive power. In all engines the great source of expense is the fuel; and although the consumption of fuel has been greatly reduced within the last ten or fifteen years, it is capable of being still further reduced by certain easy expedients of improvement, which therefore it is important should be universally applied. One of these expedients consists in heating the feed water by the waste steam; and the feed water should in every case be sent into the boiler boiling hot, instead of being quite cold, as is at present generally the case. The ports of the cylinders should be as large as possible; the expansion of the steam should be carried to a greater extent; and in the case of engines with outside cylinders, the waste steam should circulate entirely round the cylinders before escaping by the blast pipe. The escape of heat from the boiler should be more carefully prevented; and the engine should be balanced by weights on the wheels to obviate a waste of power by yawing on the rails. The most important expedient of all, however, lies in the establishment of a system of registering the performance of all new engines, in order that competition may stimulate the different constructors to the attainment of the utmost possible economy; and under the stimulus of comparison and notoriety, a large measure of improvement would speedily ensue. The benefits consequent on public competition are abundantly illustrated by the rapid diminution of the consumption of fuel in the case of agricultural engines, when this stimulus was presented.
OF VARIOUS FORMS, APPLICATIONS, AND APPLIANCES OF THE STEAM ENGINE.
In the English edition of this work, the first part of this chapter is devoted to examples of Portable and fixed Agricultural engines, of different makers and styles of workmanship, but not in sufficient detail, nor illustrated on large enough scale to be of practical value as models, forming rather in fact an illustrated catalogue of the manufacturer, than a study for the mechanic. On this account, they have been entirely omitted, and their place supplied by a few illustrations from American workmanship, not only of Steam Engines, of various forms and applications, but also of various machines, or appliances, connected with the working of engines, as for the determination, or regulation of pressure, of the boilers; for the supply or feed of the boilers, the regulation of the speed of the engine, and the like.
The Gauges used in this country to show the pressures of steam in boilers are of various constructions, but perhaps the most common is the Bourdon, or, as it is known here, the Ashcroft gauge, from the party introducing it, and holding the patent. Fig. 59 represents its interior construction. It consists of a thin metallic tube, a, bent into nearly a complete circle closed at one end, the steam being introduced at the other, at b. The effect of the pressure of the steam on the interior of the tube is to expand the circle, more or less according to the pressure, the elasticity of the metal returning the circle to its original position, when the pressure is removed. The free or closed end of the tube is connected by a link c with a lever d, at the opposite end of which is segmental gear, in gear with a pinion, on which is a hand, which marks the pressure on a dial. The dial and hand are not shown on the cut, but are on the exterior case removed to show the construction.
Fig. 60 is an elevation of a boiler with Clark's Patent Steam and Fire Regulator attached, for the control of the draft of the chimney by the pressure of steam in the boiler. It consists of a chamber, a, with a flexible diaphragm or cover on top, in communication with the boiler. On this diaphragm rests a plunger or piston, which is held down like a safety valve, by a lever and weight, b. The end of the lever is connected with a balanced damper, c, in the chimney. The weight, b, is placed at any required position on the lever, and when the pressure of steam in the boiler, exerted on the diaphragm, becomes sufficient to raise the weight, the lever rises, and the damper begins to close, and to check the draft in the chimney. When properly adjusted, the machine works on a variation of from, one to two pounds between the extremes of motion. When the dampers are very large, say 3 feet or over, they should be set on rollers, like common grindstone rollers; the regulator should be attached directly to the damper, the length of the pipe connecting the regulator with the boiler being of no account.
Porter's Patent Governor, fig. 61, is a modification of the ordinary centrifugal governor. Very small balls are employed, from 2-1/4 to 2-5/8 inches in diameter. These swing from a single joint at the axis of the spindle, which is the most sensitive arrangement, and make from 300 to 350 revolutions per minute, at which speed their centrifugal force lifts the counterpoise. The lower arms are jointed to the upper ones at the centres of the balls, and connect with the slide by joints about two inches apart. The counterpoise may be attached to the slide in any manner; for the sake of elegance, it is put in the form of a vase rising between the arms, its stem forming the slide. The vase is hollow and filled with lead, and weighs from 60 lbs. to 175 lbs. It moves freely on the spindle, through nearly twice the vertical distances traversed by the balls, and is capable of rising from 2-1/2 to 3 inches, before its rim will touch the arms. It is represented in the figure as lifted through about one half of its range of action.
The standard is bored out of the solid, forming a long and perfect bearing for the spindle; the arms and balls are of gun metal, the joint pins of steel; every part of the governor is finished bright, except the bracket carrying the lever, and the square base of the standard, which are painted. The pulley is from 3 to 10 inches in diameter, and makes in the larger sizes about 125 revolutions, and in the smaller 230 revolutions per minute; the higher speed of the governor being got up by gearing.
Mr. Porter warrants the following action in this governor, operating any regulating valve or cut-off which is in reasonably good order. The engine should be run with the stop-valve wide open, and, except the usual oiling, will require no attention from the engineer, under any circumstances, after it is started, until it is to be stopped. No increase in the pressure of steam will affect its motion perceptibly. The extreme possible variation in the speed, between that at which the regulating valve will be held wide open, and that at which it will be closed, is from 3 to 5 per cent., being least in the largest governors. This is less than 1/6 of the variation required by the average of ordinary governors, and is with difficulty detected by the senses. The entire load which the engine is capable of driving may be thrown on or off at once, and one watching the revolutions cannot tell when it is done. The governor will be sensibly affected by a variation in the motion of the engine of 1 revolution in 800. Notwithstanding this extreme sensitiveness, or rather by reason of it, it will not oscillate, but when the load is uniform will stand quite, or nearly, motionless.
For the supply of the water to the boiler, in many positions, it is very convenient to have a pump unconnected with the engine. On this account it is very usual in this country to have what are called donkey pumps or engines independent of the main engines, which can be used to feed the boilers, or for supplying water for many other purposes.
Fig. 62 is a longitudinal section of the Worthington Steam Pump, the first of its kind, and for many years in successful operation.
The general arrangement is that of a Steam Cylinder, the piston rod of which, carried through into the water cylinder and attached directly to the water plunger, works back and forth without rotary motion, and of course without using either crank or fly wheel.
In the figures, a is the Steam Cylinder—b, the Steam Chest—d, a handle for regulating the steam valve—f, the starting bar g, g, tappets attached to the valve rod, which is moved by the contact of the arm e, on the piston rod with said tappets—h, the double-acting water plunger working through a packing ring—o, o, force valves—o', o', suction valves. The pump piston is represented as moving from right to left, the arrows indicating the course of the water through the passages. The suction valves o', on the right side, and the force valves o, on the left side, are show open; x, is an air chamber made of copper; s, the suction pipe terminating in a vacuum chamber; made by prolonging the suction pipe, and closing it perfectly tight at the top, the connection being made to the pump by a branch as shown; m, m, are hand-hole plates, affording easy access to the water valves; n, n, small holes through the plunger, which relieve the pressure near the end of the stroke, to give momentum to throw the valves when working at slow speed.
Fig. 63 is a perspective view of H.R. Worthington's Duplex Steam Pump. The prominent peculiarity of this pump is its valve motion. As seen in the cut, two steam pumps are placed side by side (or end to end, if desired). Each pump, by a rock shaft connected with its piston rod, gives a constant and easy motion to the steam valve of the other. Each pump therefore gives steam to and starts its neighbor, and then finishes its own stroke, pausing an instant till its own steam valve, being opened by the other pump, allows it to make the return stroke.
This combined action produces a perfectly positive valve motion without dead points, great regularity and ease of motion, and entire absence of noise or shock of any kind. Both kinds of pumps are made by Mr. Worthington, of various size according to the requirements, the duplex being used for boiler feed and for the supply of cities with water.
Fig. 64 is a side elevation of the Woodward Steam Pump. The pump is direct acting. The steam and water piston being on the same rod, but momentum is obtained to throw the valves by means of a fly wheel, placed beyond the pump, and connected with the piston rod by a cross head and a yoke. The machine is simple in its construction and action, and is extensively used.
Giffard's Injector, both in Europe and this country, is quite extensively used to supply the place of a pump, as independent feed for all classes of boilers. It is represented in elevation and section, figs. 65 and 66.
A, steam pipe leading from the boiler. B, a perforated tube or cylinder, through which the steam passes into the space b. C screwed rod for regulating the passage of steam through the annular conical space c, and worked by the handle d/. E, suction pipe, leading from the tank or hot well to small chamber m. F, annular conical opening or discharge pipe, the size of which is regulated by the movement of the tube or cylinder B. G, hand wheel for actuating the cylinder B. H, opening, in connection with the atmosphere, intervening between discharge pipe F and the receiving pipe through which the water is forced. I, tube through which the water passes to the boiler. K, valve for preventing the return of the water from the boiler when the injector is not working. L, waste or overflow pipe. M, nut to tighten the packing rings g and upper packing i in cylinder B. N, lock nut to hold M.
The pipe A is connected with the steam space of the boiler at its highest part, to obtain as dry steam as possible. The passage of the steam into A is controlled by a cock, as is also the feed pipe to the boiler. In working, both are opened, the steam passes through A into the space b, and issuing through the nozzle c with the pressure due to its head, and a partial vacuum by its contact with the feed water, it drives this water in connection with the jet through the pipe F into the pipe I in connection with the water space of the boiler.
Method of Working.—Turn the wheel so as to permit a small quantity of water to flow to the instrument. Open the steam cock connecting the apparatus with the boiler. Turn slightly the handle, which will admit a small quantity of steam to the apparatus; a partial vacuum is thus produced, causing the water to enter through the supply pipe. As soon as this happens, which can be observed at the overflow pipe, the supply of steam or water may be increased as required, up to the capacity of the instrument, regulating either by means of the wheel and handle, so as to prevent any overflow. The quantity of water delivered into the boiler, may be varied by means of the stop cocks on the steam and water pipes, without altering the handles on the injector; a graduated cock on the water supply pipe is very convenient for this purpose.
The machines are manufactured by Wm. Sellers & Co. Philadelphia.
As an example of Portable Steam Engines, of which there are large numbers in this country of different manufacturers, we give the representation (fig. 67) of one made by J.C. Hoadley, of Lawrence, Mass.
In these machines, the rules and proportions of the locomotive engine are adapted to the requirements of stationary power, for all purposes under forty horse power. The leading ideas are: high velocity, high pressure, good valve motion, large fire-box, numerous and short flues, and steam blast. The characteristic features are: great strength of boiler, fully adequate to bear with safety 200. lbs. pressure per sq. in., great compactness and simplicity, large and adjustable wearing surfaces, and the entire absence of all finish, or polish, for mere show.
The cylinder is placed over the centre of the boiler, at the fire-box end, so that the strain due to the engine is central to the boiler (which serves as bed plate); the starting valve is under the hand of the engineer when at the fire door; and both ends of the crank shaft are available for driving pulleys.
For the sake of compactness, the cylinders are set low, by means of a depression in the boiler between the stands of the crank shaft, to admit of the play of the crank and connecting rod. All the parts are attached to the boiler, which is made of sufficient strength to bear all extra strain due to the working of the engine.
They have feed water heater, force pumps, Jackson's governor and valve, belt for governor, belt pulley, turned on the face, steam gauge; everything, in short, necessary to the convenient working of a steam engine. All engines are fired up and tried before they leave the shop, and they are warranted tight, safe, and complete.
A strong and convenient running gear, so arranged as to be easily attached and detached at pleasure, is furnished, if desired; forming, when separate, a useful wagon.
Fig. 68 is a compact vertical engine, as built by R. Hoe & Co., of this city. It is intended to drive printing presses, but is adapted to any kind of work, and is especially suited to such places as require economy of space. Although the value of expansion has been called in question by some of the engineers of the United States Navy, and under an appropriation from Congress is now to be made the subject of experiment; yet, in almost all the manufactories and workshops of the United States, no matter what the form of steam engine, or the purposes to which it is applied, whether stationary, locomotive, or marine, some form of cut-off, by which expansion of the steam can be availed of, is considered indispensable. Many varieties are in use, but those engines are most popular in which the cut-off is applied directly to the valves on the cylinder, opening them quickly and shutting off almost instantly, avoiding all wire drawing of the steam at the ports, and regulating the speed of the engine promptly. Of this class of engines, those manufactured by the Corliss Steam Engine Company, of Providence, R.I., are perhaps the widest known, not only for their extensive introduction, but also from having, by a long and successful litigation, established the claims of the patentee, Mr. George H. Corliss.
Fig. 70 is a section of the cylinder and valve chests of a horizontal Corliss engine. S is the steam connection, and E the exhaust; there are two distinct sets of valves, the steam s, s', and the exhaust e, e', operated independently of each other. In their construction the valves may be considered cylindrical plugs, of which portions near the ports are cut away to admit the steam and reduce the bearing surface; the valves are fitted on the lathe and the seats by boring. The motion given to the valves is rocking, but it will be observed that the valves are not firmly connected to the rocking shaft or cylinder; in the figure the valves are shown shade lined, and the shaft or stem plain; in this way the valves are not affected by the packing of the valve stem, but always rest upon the face of the ports. In the figure the piston is just about to commence its outstroke, the movement of the steam is supposed to be represented by the arrows; the inner steam valve s, and the outer exhaust e', are just beginning to open. It will be observed that the outer steam s' is fully closed, whilst the inner exhaust valve e is but barely so, showing that there has been a cut-off on the steam valve, but no lead to the exhaust, that it was left fully open till the completion of the stroke.
Fig. 71 is a side elevation of the cylinder, with the valve connections with the governor. S is the steam pipe; s, s' handles to the steam valves, and e, e' to the exhaust valves, shown in dotted line in fig. 70. The handles to the exhaust valves are connected directly to a rocking plate R, to which motion is given by a connection x, with an eccentric on the engine shaft. When once set, therefore the movement of the exhaust valves is constant, and they will always be opened and closed at the same point of the stroke. Connected with the rocking plate R, and on opposite sides of its centre, the same as the exhaust valve connections, there are two levers, vibrating on a centre c, of which one only is shown, as it covers the other; to the upper ends of these levers pawls are attached, one end of which rests on the stems or rods connected with the handles s, s', of the steam valves; on these stems there are notches against which the pawls strike, and as the levers vibrate inward they push back the stems and thereby open the valves, and this continues for the whole length of the inward motion of the levers, or till the outer extremities of the pawls come in contact with the end of the short lever l, which, pushing down the outer end of the pawls, relieves the stems at the other ends, and the valve stem returns to its place through the force of springs attached to the outer extremities of the valve stems a, are cylindrical guides to the valve stems, at the inner extremities of which are air cushions. The lever l is connected directly with the governor. As the balls rise, they depress the extremity, which comes in contact with the pawls sooner, and thereby shut the valves earlier; and on the contrary when the balls are depressed, the valves remain open longer; as the pawls come in contact with the stems always at one point, the steam valves open constantly, but are closed at any point by the relief of the pawls, according to the speed of the governor.
Fig. 71 represents, partly in section and partly in plan, the cylinder, steam chests, valves, &c., of one of the Woodruff & Beach high pressure Engines, Wright's patent.
Fig. 72 represents, in elevation, the cam shaft, to the upper end of which, not shown in the drawing, is attached the ordinary centrifugal governor. The cylinder, steam chests, valves, &c., being similar to those of other engines, need no special notice; but the cam for opening and closing the steam valves, fig. 72, requires particular attention, as it embodies a beautiful and simple device for cutting off the steam with certainty at any part of the stroke, the motion being produced automatically by the action of the governor on this cam, throwing it more or less out of centre with the spindle of the governor, as the rotation of the balls is less or more rapid, the eccentricity of the cam determining the amount of steam admitted to the working cylinder of the engine. To produce this effect the cam is made as follows:
C is a hollow cylinder or shell, with a part of one end formed into a cam proper. Throughout the whole length of this piece, upon the inside, there is a spiral groove cut to receive one end of a feather, by which its pitch or eccentricity is regulated. C' is also a hollow cylinder or shell, of the same length and diameter as C, with a similar spiral groove cut on the inside, the outside being perfectly smooth and plain, upon which the toe (t) for closing the valves is fastened. The inside piece consists of two hubs D, D', eccentric with each other, and made in one piece, D being turned to exactly fit the inside of the shell C, and D' to fit the shell C', the hub D' having a socket (c) into which the spindle (s) of the governor is screwed; the end (d) of the hub D forming a journal or bearing, with a bevel wheel on its extremity to convey motion from the crank-shaft gearing to the governor and cut-off. There is a hole throughout the length of the inside hubs D and D', which is continued through the spindle of the governor, and contains the rod (r) that connects the cam with the governor. This hole is eccentric to the outside surface of the hub D, as well as to the shell C, and concentric with the hub D' and shell C', and with the governor rod (r).
The shell C and hub D, and shell C' and hub D', are connected together by feathers; one piece of each feather is of a spiral form, and the other a straight or rectangular piece, the two being connected together by a stub on the rectangular piece, which fits into a hole or bearing in the other or spiral piece, so that the latter can turn on the stub and accommodate itself to the groove in which it has to work. The spiral part of each feather works in the spiral groove on the inside of its corresponding shell C and C' respectively, and the rectangular pieces work in a straight groove cut in the hubs D and D', the inner parts of the rectangular pieces being fastened to the governor rod (r), so that the feathers are permanently connected with the governor.
The shell C' revolves inside of two yokes (y) and (y'), one attached to each steam-valve toe, (a) and (a') respectively.
On the inside of each yoke, and opposite to its valve-toe, is a raised piece, against which the closing piece (t) on the shell (C') acts to close the valves.
This shell (C'), as before noticed, has a spiral groove on its inside, similar in all respects to that in the cam-shell (C); and being acted upon in the same manner and through the same rod by the governor, it is evident that the closing piece (t) on its outside will always hold the same relation to the opening toe on the lower or cam-shell (C); and whatever alteration is made in the one, a corresponding alteration takes place in the other, thereby insuring the closing of the valves at the proper time at every point of the variation of the cut-off.
When the several pieces above described are put together, the apparatus for opening and closing the valves and producing the cut-off is complete, as shown in fig. 72, and it operates as follows:
Motion is communicated by gearing from the crank-shaft to the bevel wheel on the piece (d) on the end of the hub D, and is communicated to the spindle of the governor, which is screwed into the socket on D'. As the balls rise or fall, through change of centrifugal force due to the variation in the speed of rotation, they raise or depress the governor-rod, which passes through the spindle and the hubs D' and D, and is attached to the feathers, thereby raising or depressing the feathers, which, acting on their respective spiral grooves, instantly alters the lift of the cam on the shell (C), and brings the closing toe (t) on the shell (C') into proper position for closing, and so regulates the amount of steam admitted to the cylinder.
Consequently, any speed may be selected at which the load of the engine is to move, and any variation from that will be instantly felt by the governor, and corrected by this simple and beautiful device. There is no jar in the working of the parts; the feathers move noiselessly in their grooves; the governor rod moves up and down through the spindle and the hubs D and D', and can be regulated by hand to give any required opening of the steam ports to suit the work to be done. Any change in the amount of work will then alter the speed of the engine, and so affect the governor and cam, as before said.
It is unnecessary to insist on the great economy attained by using steam with a well-regulated cut-off, for practical men know now that the essential points of excellence in the steam engine are a good boiler, which generates the greatest quantity of steam for the least consumption of fuel; and, secondly, a reliable cut-off, which uses the steam to the best advantage, by admitting the proper quantity for the work required.
STEAM FIRE ENGINES.—Portable engines for the extinguishment of fires, are an American invention, and to Messrs. A.B. & E. Latta, of Cincinnati, working on the right principles, is due the credit which they claim in their circular, as follows:
"We claim to be the original and first projectors of the first successful steam fire engine in the world's history. There have been many attempts at making a machine of such construction as would answer to extinguish fires; but none of them proved to be available in a sufficiently short space of time to warrant their use as a fire apparatus. We hold that a steam fire engine should be of such nature as to be brought into requisition in as short a space of time as is necessary to get the machine on the ground, and the hose laid and ready to work: that is, supposing the fire to be within one square of the place where the steamer is located. The object in locating a machine at any point is to protect that immediate vicinity; and it is therefore absolutely necessary to have it available in the shortest space of time, and that with unerring certainty. We think that reliability is of the greatest importance to the protection of a city from fire, as everything is dependent on the working of such apparatus in time; and for this reason no expense should be spared on this kind of machinery."
Fig. 73 is a representation of one of the Messrs. Latta's fire engines, of which there are many of different classes, according to the requirements; they say that they can furnish engines as low as $1,000, and have made some for $10,000.
The first peculiar feature of this engine is the boiler; it differs entirely from all boilers now in use.
The fire box or furnace is simply a square box or furnace of any required dimensions; it is nothing more than a water space surrounding the fire, stay-bolted as all water spaces are. It is made of boiler plate in the usual manner. The water space extends only 2/3 of the height, the balance being a single sheet. The bottom of this fire box is crossed by grate bars to support the fuel; in its rear side are fire doors, inserted for firing. The internal arrangements of the boiler are composed of a large number of tubes, lying across in a horizontal position, put together in sections with return bends resembling the coils for heating buildings. These coils are of small pipe (say one inch in diameter), and as numerous as may be necessary. They give the required amount of steam. They are secured to wrought-iron plates at each end by rivets. These plates lie close to the box, and are secured to it, top and bottom. These tubes are wrought iron, firmly screwed into the bends, so as to prevent any possible breaking.
The box has a hole through both sheets, in the same manner as a hollow stay-bolt, through which the coil pipe passes, having no connection with the box. After passing into the box it divides into two pipes, then subdivides into four, and so on, until its numbers equal the number of coils in the box, and to which each limb is attached. The upper ends of these coils are the same in number, and are carried through at the top or nearly the top of the box. They then run down outside to the steam chamber, or rather water space, as the box is both steam chamber and water space. These pipes empty their contents into the box, steam and water, as it may come, all together. It will be observed that these coils of tube are sufficiently separated to allow the fire to pass between them freely, and cover their whole surface.
The mode of operation of this boiler is this: The fire box is filled 2/3 full of water. The coils are dry at starting; the space for fuel being filled with good wood, the fire is lighted, and in a few moments the engineer moves his hand pump, which takes its water from the box to which it is attached, and forces it through the coils. By this means steam is generated in from 3 to 5 minutes, so as to start the engine.
It will be seen that the water performs a complete circuit; it is taken from the box and passed through the coils; what is steam remains in the steam chamber, and what is not (if any) drops back into the box from where it started. Hence it will be seen that a large surface is exposed to a small quantity of water, and in a way that it is entirely controllable. All the engineer has to do to surcharge his steam, is to reduce the speed of the pump (which is independent of the main engine). By raising the heat and quantity of water, any degree of elasticity can be given to the steam, and that, too, with the least amount of waste heat in giving a natural draft. Hence the great economy of this boiler.
The next feature of this engine is, it has no wood work about it to perish with the heat and roughness of the streets. All the wheels are wrought iron; and, as yet, these are the only ones that have stood a steam fire engine. The frame is wrought iron; truck, on which the front wheel is hung, wrought iron. The axles are cast steel. The engine and pump is a double-acting piston pump direct, without any rotary motion; with a perfect balance valve, it is balanced at all times, and hence the engine remains quiet without blocking, when at work. The engine is mounted on three wheels, which enables it to be turned in a very short space.
Many engines have been constructed by the Messrs. Latta for the fire companies, of different cities, and have been in successful competition with other engines; the farthest throw ever made by one of their first-class engines was 310 feet from a 1-5/8 inch nozzle; steaming time, starting from cold water, 3-1/2 minutes.
Fig. 74 is a representation of one class of steam fire engine, as built by the Amoskeag Manufacturing Company, at Manchester, N.H. The boiler is an upright tubular boiler, of a peculiar construction, the patent right to which is vested in the Amoskeag Manufacturing Company. This boiler is very simple in its combination, and for safety, strength, durability, and capacity for generating steam is unsurpassed. No fan or artificial blower is ever used or needed, the natural draft of the boiler being always sufficient. Starting with cold water in the boiler, a working head of steam can be generated in less than five minutes from the time of kindling the fire. The engine "Amoskeag," owned by the city of Manchester, has played two streams in three minutes and forty seconds after touching the match, at the same time drawing her own water. The boilers are made and proved so as to be safely run at a steam pressure of 140 to 150 lbs. to the square inch; but the engines are constructed so as to give the best streams at a pressure of about 100 lbs. to the square inch, and for service at fires a steam pressure of about 60 lbs. to the square inch is all that is required.
The various styles of engine are all vertical in their action, and in all the pumps and steam cylinders are firmly and directly fastened to the boiler, the steam cylinders being attached directly to the steam dome. This arrangement obviates the necessity of carrying steam to the cylinders through pipes of considerable length, and the machine has very little vibratory motion when in operation—so little that it is not necessary to block its wheels to keep it in its place, or to take the weight off the springs before commencing work.
The pumps are placed on the engines as near the ground as they can be with safety, and are arranged so as to attach the suction and leading hose to either or both sides of the machine, as may be most convenient or desirable, so that less difficulty will be found in placing an engine for work, and when required to draw its own water, it has only to draw it the shortest possible distance.
Each engine has two "feed pumps" for supplying the boiler, and also a connection between the main forcing pumps and the boiler, so that it can be supplied from that source if desirable. The tank which carries the water for supplying the boiler is so placed that the water in it is always above the "feed pumps," an advantage that insures the almost certain working of these pumps. These pumps are of brass, the best locomotive pattern, and one of them running with the engine, when at work, furnishes an ample supply of water to the boiler.
The engines are exceedingly portable; they can be turned about or placed for service in as contracted a space as any hand engine, and two good horses will draw a first-class engine with the greatest ease, carrying at the same time water for the boiler, a supply of fuel sufficient to run the engine two hours, the driver, the engineer, and the fireman.
Fig. 75 is a representation of the class of steam fire engine built by Silsbee, Mynderse & Co., Seneca Falls, N. Y. under Holly's patent.
The boiler is vertical, with vertical water tubes passing directly through the fire. These tubes are closed at the bottom and open at the top, where they pass through a water-tight plate, and communicate with the water in the boiler. The arrangement of the tubes causes a constant current, the water rising on the outside of the tubes as they are heated, and its place being supplied by a current flowing downward through the tube to the boiler. The smoke and flame pass among the tubes up through flues.
Both engine and pump are rotary, and of the same type. They consist essentially of two elliptical rotary pistons, cogged and working into one another in an air-tight case. The pistons fit close to the inside of the case, and gear into each on the line of their conjugate diameters. The action is somewhat similar to the old-fashioned rotary pump, consisting of two cog wheels in gear with, each other, the spaces at the side of the case being filled with water, which at the centre are occupied by the teeth in gear. In Holly's pump, instead of uniform teeth, and depending on the fit of the teeth with the side of the case and with each other for the packing, there are two large teeth in each piston opposite each other, which have slide pistons, and intermediate with these large teeth are small cogs, which continue the motion of the rotary pistons. The machine works very smoothly, and performs the work necessary, in ordinary service, under a pressure of 50 to 60 lbs.
There are many other makers of fire engines in this country; but sufficient examples are given to illustrate the class; so successful have they been, that they are fast superseding hand engines, even in the smaller cities.
Under a paid department, the following is, in the city of Boston, Mass., the comparative cost of running the two kinds of engines, viz.:
STEAM FIRE ENGINE. 1 engineer........................................... $720 00 1 fireman............................................ 600 00 1 driver............................................. 600 00 1 foreman of hose.................................... 150 00 8 hosemen, at $125 each.............................. 375 00 — ———— 7 men................................................ $2,445 00 Keeping of 2 horses.................................. 315 00 ———— Total......................................... $2,760 00
HAND ENGINE. 1 foreman............................................ $150 00 1 assistant foreman.................................. 125 00 1 clerk.............................................. 125 00 1 steward............................................ 125 00 3 leading hosemen, at $125 each...................... 375 00 33 men, at $100 each................................. 3,300 00 — ————- 40 men............................................... $4,200 00
Here the engineer, fireman, and driver are constantly employed, the hosemen have other employment in the neighborhood, but all the company sleep in the engine house.
In the city of Manchester, N.H., a steam fire engine company is composed of fourteen men, all told, one of whom, acting as driver and steward, is constantly employed, remaining at the engine house with a pair of horses always ready to run out with the engine in case of an alarm of fire. The other members of the company have other employments, and turn out only on an alarm of fire.
STEAM FIRE ENGINES. "Amoskcag," Expenditures..................... $864 32 "Fire King," " ..................... 855 78 "E.W. Harrington," " ..................... 496 09
The above expense includes pay of members, team expenses, cost of gas, wood, coal, and all necessities incident to service. The "E.W. Harrington" is a second-class engine, stationed in the outskirts of the city, and was run cheaper from the fact that no horses were kept for it by the city.
A first-class hand-engine company is allowed to number, all told, fifty men, and the members of the company are paid as follows:
FIRST-CLASS HAND-ENGINE COMPANY. 1 foreman.......................................... $35 00 1 assistant foreman............................... 28 00 1 clerk........................................... 28 00 1 steward........................................ 68 00 46 men, at $18 each................................ 828 00 ———— 50 men. Total.............................. $987 00
By this it will be seen, that in a city like Manchester, with from twenty to twenty-five thousand inhabitants, a first-class steam fire engine can be run at an expense not to exceed that of a first-class hand engine, while in service it will do at least four times the work. The cost of repairs is found by experience to be no greater on the steam fire engines than on hand engines.
The Excavator, fig. 76, is the invention of the late Mr. Otis, an application of the spoon dredging machine of the docks to railway purposes, with very important modifications. The machine consists of a strong truck, A, A, mounted on railway wheels, on which is placed the boiler C, the crane E, and the requisite gearing. The excavator or shovel, D, is a box of wrought iron, with strong points in front to act as picks in loosening the earth, and its bottom hung by a hinge at d, so that, by detaching a catch, it may fly open and discharge the material raised. To operate the machine, suppose the shovel D to be in the position shown in the cut; it is lowered by the chains o, o, and thrown forward or backward, if necessary, by the drum B, and handle S, till the picks in the front of the shovel are brought in proper contact with the face of the cut; motion forward is now given to the shovel by the drum B and handle S, and at the same time it is raised by the chains o, o. These two motions can be so adjusted to each other, as to give movement to the shovel to enable it to loosen and scrape up a shovelful of earth. The handle S is now left free, and the shovel D is raised vertically by the chains o, o. The crane is now turned round, till the shovel comes over a rail car on a side track; the bottom of the shovel is opened, and the dirt deposited in the car. All these motions are performed by the aid of a steam engine, and are controlled by a man who stands on a platform at f.
692. Q.—Having now described the most usual and approved forms of engines applicable to numerous miscellaneous purposes for which a moderate amount of steam power is required, will you briefly recapitulate what amount of work of different kinds an engine of a given power will perform, so that any one desiring to employ an engine to perform a given amount of work, will be able to tell what the power of such engine should be?
A.—It will of course be impossible to recapitulate all the purposes to which engines are applicable, or to specify for every case the amount of power necessary for the accomplishment of a given amount of work; but some examples may be given which will be applicable to the bulk of the cases occurring in practice.
693. Q.—Beginning, then, with the power necessary for threshing,—a 4 horse power engine, with cylinder 6 inches diameter, pressure of steam 45 lbs., per square inch, and making 140 revolutions per minute, will thresh out 40 quarters of wheat in 10 hours with a consumption of 3 cwt. of coals.
A.—Although this may be done, it is probably too much to say that it can be done on an average, and about three fourths of a quarter of wheat per horse power would probably be a nearer average. The amount of power consumed varies with the yield.
Messrs. Barrett, Exall, and Andrewes give the following table as illustrative of the work done, and the fuel consumed by their portable engines; but this must be regarded as a maximum performance:—
Number of Weight of Quarters of Quantity of Quantity of Horse Power. Engine. Corn thrashed Coals consumed Water required in 10 Hours. in 10 Hours. for 10 Hours in Gallons. - - - Tons. Cwts. Cwts. 4 2 0 40 3 360 5 2 5 50 4 380 6 2 10 60 5 460 7 2 15 70 6 540 8 3 0 80 7 620 10 3 10 100 9 780 -
694. Q.—In speaking of horses power, I suppose you mean indicator horse power?
A.—Yes; or rather the dynamometer horse power, which is the same, barring the friction of the engine. At the shows of the Royal Agricultural Society, the power actually exerted by the different engines is ascertained by the application of a friction wheel or dynamometer.
695. Q.—Can you give any other examples of the power necessary for grinding corn?
A.—An engine exerting 23-1/3 horses power by the indicator works two pairs of flour stones of 4 feet 8 inches diameter, two pairs of stones grinding oatmeal of 4 feet 8 inches diameter, one dressing machine, one pair of fanners, one dust screen, and one sifting machine. One of the flour stones makes 85, and the other 90 revolutions in the minute. One of the oatmeal stones makes 120, and the other 140 revolutions in the minute. To take another case:—An engine exerting 26-1/2 indicator horses power works two pairs of flour stones, one dressing machine, two pairs of stones grinding oatmeal, and one pair of shelling stones. The flour stones, one pair of the oatmeal stones, and shelling stones, are 4 feet 8 inches diameter. The diameter of the other pair of oatmeal stones is 3 feet 8 inches. The length of the cylinder of the dressing machine is 7 feet 6 inches. The flour stones make 87 revolutions in the minute, and the larger oatmeal stone 111 revolutions, but the smaller oatmeal stone and the shelling stone revolve faster than this. At the time the indicator diagram was taken, each pair of flour stones was grinding at the rate of 5 bushels an hour; each pair of oatmeal stones about 24 bushels an hour; and the shelling stones were shelling at the rate of about 54 bushels an hour. The fanners and screen were also in operation.
696. Q.—Have you any other case to enumerate?
A.—I may mention one in which the power of the same engine was increased by giving it a larger supply of steam. The engine when working with 8.65 horses power, gives motion to one pair of oatmeal stones of 4 feet 6 inches diameter, and one pair of flour stones 4 feet 8 inches diameter. The oatmeal stone makes 100 revolutions in the minute, and the flour stone 89. The oatmeal stones grind about 36 bushels in the hour, and the flour stones 5 bushels in the hour. The engine when working to 12 horses power drives one pair of flour stones, 4 feet 8 inches diameter, at 89 revolutions per minute and one pair of stones of the same diameter at 105 revolutions, grinding beans for cattle. The flour mill stones with this proportion of power, being more largely fed, ground 6 bushels per hour, and the other stones also ground 6 bushels per hour. When the power was increased to 18 horses, and the engine was burdened in addition with a dressing machine having a cylinder of 19 inches diameter, the speed of the flour stone fell to 85, and of the beans stone to 100 revolutions per minute, and the yield was also reduced. The dressing machine dressed 24 bushels per hour.
697. Q.—What is the power necessary to work a sugar mill such as is used to press the juice from canes in the West Indies?
A.—Twenty horses power will work a sugar mill having rollers about 5 feet long and 28 inches diameter; the rollers making 2-1/3 turns in a minute. If the rollers be 26 inches diameter and 4-1/2 feet long, 18 horses power will suffice to work them at the same speed, and 16 horses power if the length be reduced to 3 feet 8 inches. 12 horses power will be required to work a sugar mill with rollers 24 inches diameter and 4 feet 2 inches long; and 10 horses power will suffice if the rollers be 3 feet 10 inches long and 23 inches diameter. The speed of the surface of sugar mill rollers should not be greater than 16 feet per minute, to allow time for the canes to part with their juice. In the old mills the speed was invariably too great. The quantity of juice expressed will not be increased by increasing the speed of the rollers, but more of the juice will pass away in the begass or woody refuse of the cane.
698. Q.—What is the amount of power necessary to drive cotton mills?
A.—An indicator or actual horse power will drive 305 hand mule spindles, with proportion of preparing machinery for the same; or 230 self-acting mule spindles with preparation; or 104 throstle spindles with preparation; or 10-1/2 power looms with common sizing. The throstles referred to are the common throstles spinning 34's twist for power loom weaving, and the spindles make 4000 turns per minute. The self-acting mules are Robert's, about one half spinning 36's weft, and spindles revolving 4800 turns per minute; and the other half spinning 36's twist, with the spindles revolving 5200 times per minute. Half the hand mules were spinning 36's weft, at 4700 revolutions, and the other half 36's twist at 5000 revolutions per minute. The average breadth of the looms was 37 inches, weaving 37 inch cloth, making 123 picks per minute,—all common calicoes about 60 reed, Stockport count, and 68 picks to the inch. To take another example in the case of a mill for twisting cotton yarn into thread:—In this mill there are 27 frames with 96 common throstle spindles in each, making in all 2592 spindles. The spindles turn 2200 times in a minute; the bobbins are 1-7/8 inches diameter, and the part which holds the thread is 2-3/16 inches long. In addition to the twisting frames the steam engine works 4 turning lathes, 3 polishing lathes, 2 American machines for turning small bobbins, two circular saws, one of 22 and the other of 14 inches diameter, and 24 bobbin heads or machines for filling the bobbins with finished thread. The power required to drive the whole of this machinery is 28-1/2 horses. When all the machinery except the spindles is thrown off, the power required is 21 horses, so that 2592, the total number of spindles, divided by 21, the total power, is the number of twisting spindles worked by each actual horse power. The number is 122.84.
699. Q.—What work will be done by a given engine in sawing timber, pressing cotton, blowing furnaces, driving piles, and dredging earth out of rivers?
A.—A high pressure cylinder 10 inches diameter, 4 feet stroke, making 35 revolutions with steam of 90 to 100 lbs. on the square inch, supplied by three cylindrical boilers 30 inches diameter and 20 feet long, works two vertical saws of 34 inches stroke, which are capable of cutting 30 feet of yellow pine, 18 inches deep, in the minute. A high pressure cylinder 14 inches diameter and 4 feet stroke, making 60 strokes per minute with steam of 40 lbs. on the square inch, supplied by three cylindrical boilers without flues, 30 inches diameter and 26 feet long, with 32 square feet of grate surface, works four cotton presses geared 6 to 1, with two screws in each, of 7-1/2 inches diameter and 1-5/8 pitch, which presses will screw 1000 bales of cotton in the twelve hours. Also one high pressure cylinder of 10 inches diameter and 3 feet stroke, making 45 to 60 revolutions per minute, with steam of 45 to 50 lbs. per square inch, with two hydraulic presses having 13 inch rams of 41 feet stroke, and force pumps 2 inches diameter and 6 inches stroke, presses 30 bales of cotton per hour. One condensing engine with cylinder 56 inches diameter, 10 feet stroke, and making 15 strokes per minute with steam of 60 lbs. pressure per square inch, cut off at 1/4th of the stroke, supplied by six boilers, each 5 feet diameter, and 24 feet long, with a 22-inch double-return flue in each, and 198 square feet of fire grate, works a blast cylinder of 126 inches diameter, and 10 feet stroke, at 15 strokes per minute. The pressure of the blast is 4 to 5 lbs. per square inch; the area of pipes 2300 square inches, and the engine blows four furnaces of 14 feet diameter, each making 100 tons of pig iron per week. Two high pressure cylinders, each of 6 inches diameter and 18 inches stroke, making 60 to 80 strokes per minute, with steam of 60 Lbs. per square inch, lift two rams, each weighing 1000 lbs., five times in a minute, the leaders for the lift being 24 feet long. One high pressure cylinder of 12 inches diameter and 5 feet stroke, making 20 strokes per minute, with steam of 60 to 70 lbs. pressure per square inch, lifts 6 buckets full of dredging per minute from a depth of 30 feet below the water, or lifts 10 buckets full of mud per minute from a depth of 18 feet below the water.
MANUFACTURE AND MANAGEMENT OF STEAM ENGINES.
CONSTRUCTION OF ENGINES.
700. Q.—What are the qualities which should be possessed by the iron of which the cylinder of steam engines are made?
A.—The general ambition in making cylinders is to make them sound and hard; but it is expedient also to make them tough, so as to approach as nearly as possible to the state of malleable iron. This may be done by mixing in the furnace as many different kinds of iron as possible; and it may be set down as a general rule in iron founding, that the greater the number of the kinds of metal entering into the composition of any casting, the denser and tougher it will be. The constituent atoms of the different kinds of iron appear to be of different sizes, and the mixture of different kinds maintains the toughness, while it adds to the density and cohesive power. Hot blast iron was at one time generally believed to be weaker than cold blast iron, but it is now questioned whether it is not the stronger of the two. The cohesive strength of unmixed iron is not in proportion to its specific gravity, and its elasticity and power to resist shocks appear to become greater as the specific gravity becomes less. Nos. 3 and 4 are the strongest irons. In most cases, iron melted in a cupola is not so strong as when remelted in an air furnace, and when run into green sand it is not reckoned so strong as when run into dry sand, or loam. The quality of the fuel, and even the state of the weather, exerts an influence on the quality of the iron: smelting furnaces, on the cold blast principle, have long been known to yield better iron in winter than in summer, probably from the existence of less moisture in the air; and it would probably be found to accomplish an improvement in the quality of the iron if the blast were made to pass through a vessel containing muriate of lime, by which the moisture of the air would be extracted. The expense of such a preparation would not be considerable, as, by subsequent evaporation, the salt might be used over and over again for the same purpose.
701. Q.—Will you explain the process of casting cylinders?
A.—The mould into which the metal is poured is built up of bricks and loam, the loam being clay and sand ground together in a mill, with the addition of a little horse-dung to give it a fibrous structure and prevent cracks. The loam board, by which the circle of the cylinder is to be swept, is attached to an upright iron bar, at the distance of the radius of the cylinder, and a cylindrical shell of brick is built up, which is plastered on the inside with loam, and made quite smooth by traversing the perpendicular loam board round it. A core is then formed in a similar manner, but so much smaller as to leave a space between the shell and the core equal to the thickness of the cylinder, and into this space the melted metal is poured. Whatever nozzles or projections are required upon the cylinder, must be formed by means of wooden patterns, which are built into the shell, and subsequently withdrawn; but where a number of cylinders of the same kind are required, it is advisable to make these patterns of iron, which will not be liable to warp or twist while the loam is being dried. Before the iron is cast into the mould, the interior of the mould must be covered with finely powdered charcoal—or blackening, as it is technically termed; and the secret of making finely skinned castings lies in using plenty of blackening. In loam and dry sand castings the charcoal should be mixed with thick clay water, and applied until it is an eighth of an inch thick, or more; the surface should be then very carefully smoothed or sleeked, and if the metal has been judiciously mixed, and the mould thoroughly dried, the casting is sure to be a fine one. Dry sand and loam castings should be, as much as possible, made in boxes; the moulds may thereby be more rapidly and more effectually dried, and better castings will be got with a less expense.
702. Q.—Will you explain the next operation which a cylinder undergoes?
A.—The next stage is the boring; and in boring cylinders of 74 inches diameter, the boring bar must move so as to make one revolution in about 4-1/2 minutes, at which speed the cutters will move at the rate of about 5 feet per minute. In boring brass, the speed must be slower; the common rate at which the tool moves in boring brass air pumps is about 3 feet per minute. If this speed be materially exceeded the tool will be spoiled, and the pump made taper. The speed proper for boring a cylinder will answer for boring the brass air pump of the same engine. A brass air pump of 36-1/2 inches diameter requires the bar to make one turn in about three minutes, which is also the speed proper for a cylinder 60 inches in diameter. To bore a brass air pump 36-1/2 inches in diameter requires a week, an iron one requires 48 hours, and a copper one 24 hours. In turning a malleable iron shaft 12-3/4 inches in diameter, the shaft should make about five turns per minute, which is equivalent to a speed in the tool of about 16 feet per minute; but this speed may be exceeded if soap and water be plentifully run on the point of the tool. A boring mill, of which the speed may be varied from one turn in six minutes to twenty-five turns in one minute, will be suitable for all ordinary wants that can occur in practice.
703. Q.—Are there any precautions necessary to be observed in order that the boring may be truly effected?
A.—In fixing a cylinder into the boring mill, great care must be taken that it is not screwed down unequally; and indeed it will be impossible to bore a large cylinder in a horizontal mill without being oval, unless the cylinder be carefully gauged when standing on end, and be set up by screws when laid in the mill until it again assumes its original form. A large cylinder will inevitably become oval if laid upon its side; and if while under the tension due to its own weight it be bored round, it will become oval again when set upon end. If the bottom be cast in, the cylinder will be probably found to be round at one end and oval at the other, unless a vertical boring mill be employed, or the precautions here suggested be adopted.
704. Q.—Does the boring tool make the cylinder sufficiently smooth for the reception of the piston?
A.—Many engine makers give no other finish to their cylinders; but Messrs. Penn grind their cylinders after they are bored, by laying them on their side, and rubbing a piece of lead, with a cross iron handle like that of a rolling stone, and smeared with emery and oil, backward and forward— the cylinder being gradually turned round so as to subject every part successively to the operation. The lead by which this grinding is accomplished is cast in the Cylinder, whereby it is formed of the right curve; but the part of the cylinder in which it is cast should be previously heated by a hot iron, else the metal may be cracked by the sudden heat.
705. Q.—How are the parts of a piston fitted together so as to be perfectly steam tight?
A.—The old practice was to depend chiefly upon grinding as the means of making the rings tight upon the piston or upon one another; but scraping is now chiefly relied on. Some makers, however, finish their steam surfaces by grinding them with powdered Turkey stone and oil. A slight grinding, or polishing, with powdered Turkey stone and oil, appears to be expedient in ordinary cases, and may be conveniently accomplished by setting the piston on a revolving table, and holding the ring stationary by a cross piece of wood while the table turns round. Pieces of wood may be interposed between the ring and the body of the piston, to keep the ring nearly in its right position; but these pieces of wood should be fitted so loosely as to give some side play, else the disposition would arise to wear the flange of the piston into a groove.
706. Q.—What kind of tool is used for finishing surfaces by scraping?
A.—A flat file bent, and sharpened at the end, makes an eligible scraper for the first stages; or a flat file sharpened at the end and used like a chisel for wood. A three-cornered file, sharpened at all the corners, is the best instrument for finishing the operation. The scraping tool should be of the best steel, and should be carefully sharpened at short intervals on a Turkey stone, so as to maintain a fine edge.
707. Q.—Will you explain the method of fitting together the valve and cylinder faces?
A.—Both faces must first be planed, then filed according to the indications of a metallic straight edge, and subsequently of a thick metallic face plate, and finally scraped very carefully until the face plate bears equally all over the surface. In planing any surface, the catches which retain the surface on the planing machine should be relaxed previously to the last cut, to obviate distortion from springing. To ascertain, whether the face plate bears equally, smear it over with a little red ochre and oil, and move the face plate slightly, which will fix the color upon the prominent points. This operation is to be repeated frequently; and as the work advances, the quantity of coloring matter is to be diminished, until finally it is spread over the face plate in a thin film, which only dims the brightness of the plate. The surfaces at this stage must be rubbed firmly together to make the points of contact visible, and the higher points will become slightly clouded, while the other parts are left more or less in shade. If too small a quantity of coloring matter be used at first, it will be difficult to form a just conception of the general state of the surface, as the prominent points will alone be indicated, whereas the use of a large quantity of coloring matter in the latter stages would destroy the delicacy of the test the face plate affords. The number of bearing points which it is desirable to establish on the surface of the work, depends on the use to which the surface is to be applied; but whether it is to be finished with great elaboration, or otherwise, the bearing points should be distributed equally over the surface. Face plates, or planometers, as they are sometimes termed, are supplied by most of the makers of engineering tools. Every factory should be abundantly supplied with them, and also with steel straight edges; and there should be a master face plate, and a master straight edge, for the sole purpose of testing, from time to time, the accuracy of those in use.
708. Q.—Is the operation of surfacing, which you have described, necessary in the case of all slide valves?
A.—Yes; and in fitting the faces of a D valve, great care must, in addition, be taken that the valve is not made conical; for unless the back be exactly parallel with the face, it will be impossible to keep the packing from being rapidly cut away. When the valve is laid upon the face plate, the back must be made quite fair along the whole length, by draw filing, according to the indications of a straight edge; and the distance from the face to the extreme height of the back must be made identical at each extremity.