With this experimental engine Mr. Smeaton made a multitude of experiments, which he noted down with great care in tables, and from their results deduced rules for the proportions of the parts of bis engine: he afterwards erected many engines of the largest dimensions, which fully verified his experiments. It may be here remarked, that in the year 1765 this talented engineer made a portable steam-engine, for draining foundations or other temporary works : it had a pulley or wheel to receive the chain, which communicated motion from the piston to the pump-rod, instead of a beam ; and the whole machine being supported in one frame of wood, shaped like the letter V inverted; it had no connexion with the building in which it was placed, or it could work altogether in the open air. The boiler required no setting in brick-work, but was in the shape of a large tea-kettle, and the fire was in the centre of it, surrounded on all sides by the water.
The annexed wood-cut (see page 710) and description, furnish a represen tation of the atmospheric engine of Newcomen, under the combined improve ments of Beighton and Smeaton. The boiler, the sucking-pump and its apparatus, are not given, as being unnecessary to the clear understanding of this contrivance.
C the steam pipe through which the steam passes from the boiler to the receiver D, a close iron vessel or box, in which is the regulator, or steam-cock, to open and shut the communication with the cylinder Fat each stroke; E the communication pipe between the receiver and the cylinder, rising five or six inches up in the inside of the cylinder above the bottom, to prevent the injected water from descending into the receiver ; F the cylinder of cast iron, about ten feet long, bored smooth in the inside; it has a broad flanch in the middle, on the outside, by which it is supported upon the cylinder beams, that extend across the house, and are let into the side wall; G the piston, made to fit the cylinder exactly, but with liberty to slide up and down ; a flanch rises four or five inches upon its upper surface, between which and the side of the cylinder a quantity of junk or oakum is stuffed, and kept down by weights, to prevent the entrance of air or water, and the escape of steam. H the piston shank, connected by a chain to the working-beam I I, which is suspended on its centre in the manner of a scale-beam. The arch ends of the beam (one only is here shown) are for giving a perpendicular direction to the chains of the piston and pump rods. N the jaek-head sucking pump, for supplying injection water to the cistern o, and wrought by a small lever or working-beam connected to the great beam. o the jack-head cistern, always kept full by the pump N, and raised to such a height above the bottom of the cylinder F as to give the jet of injection a sufficient force into the cylinder. When the cock is opened, a waste-pipe is connected with the cistern, to carry off the superfluous water. P P the injection pipe, two or three inches in diameter, descending from the cistern o to the injection cock r, after passing which it turns up in a curve at the lower end, and enters the cylinder ; it has a thin plate of iron screwed upon the end d, pierced with three or four holes to disperse the injection water uithin the cylinder in so many streams, for the readier condensation of the f a small pipe branching off from the injection pipe P, to supply the upper surface of the piston with water, to keep it air-ught. Q the working plug, suspended by a chain to the small arch g of the working beam ; it is usually a heavy piece of timber, with a slit vertically down its middle, and boles bored horizontally through it to receive pins, for the purpose of opening .
and shutting the injection and steam cocks, as it ascends and descends, by the motion of the working beam. h the handle of the steam cock or regulator ; it is fixed to the regulator by a spindle, which comes up through the top of the receiver. The regulator itself is a sectorialplate of brass, shaped like a fan, and moved horizontally by the handle h, and opens or shuts the communication at the lower end of the pipe E within the receiver. i i the spanner, a long rod ur bar of iron, for communicating motion to the handle of the regulator, to which it is fixed by means of a slit in the latter, and some pins put through to fasten it. k 1 the vibrating lever, called the tumbling-bob, having the weight k
at one end and the two forked legs at the other, like the letter Y turned. It is fixed to an horizontal axis, movable about its centre pins m a, and is put in motion by means of the two shanks o p, fixed to the same axis, which are alter nately raised and depressed by means of two pins in the working plug, and the bob, or weight at the top of the Y, is thrown backwards and forwards; one pin on the outside, depressing the shank o, throws the loaded end k of the Y from the cylinder into the position represented in the wood-cut, and causes the leg 1 of the fork of the Y to strike against the end of the spanner, which, forcing back the handle of the regulator or steam-cock, opens the communication, and permits the steam to rush into the cylinder. The piston immediately rises by the weight of the pump rod, on the admission of the steam ; the motion of the working beam I I also raises the working plug; and another pin, which goes through the slit, raises the shank p of the axis, which throws the end k of the Y towards the cylinder, and the leg of the fork, striking the end of the spanner, forces it forward, and shuts the regulator or steam cock. g r is the lever for opening and shutting the injection cock called the F. It has a rack or toothed sector fixed upon its axis, which takes the teeth of a pinion fixed on the top of the plug-or key of the injection cock. When the working plug has ascended nearly to its greatest height, and shut the regulator as above described, a pin catches the end q of the F, and raises it up, which opens the injection cock, and admits a 'et of cold water to rush into the cylinder ; and, condensing the steam, makes a vacuum or void within. Then the pressure of the atmosphere forcing down the piston into the cylinder, causes the plug frame to descend, and another pin fixed in it catches the end of the lever g in its descent, and, by pressing it down, abuts the injection cock; at the same time the regulator is opened to admit steam, and so on alternately ; that when the regulator is shut, the injection cock shall he open, and when the former is open the latter shall be shut. R the eduction pipe, to convey away the water which is injected into the cylinder at each stroke ; its upper end is even with the cylinder bottom, and its lower end has .a lid or cover, movable on a hinge, which serves as a valve to let out the injected water, and shuts close each stroke of the engine, to prevent the water being forced-up again when the void is made. S, the hot well, a small cistern made of planks to receive all the waste water from the cylinder, and keep it in reserve fur feeding the boiler, to oupply the waste occasioned by the continual evapora tion of the steam. T, the feeding pipe to supply the boiler with water from the hot well. W, the waste pipe which conducts the superfluous water from the top of the cylinder to the hot well S. a, the snifting valve, by which, at every ascent of the piston, the air is discharged from the cylinder which was admitted with the injection, and would otherwise obstruct the operation of the engine. t t the cylinder beams, which are strong girders going through the house for supporting, or rather keeping down the cylinder. o (erroneously marked r), a ridge of lead surrounding the top of the cylinder to the water on the piston from flashing over when it rises too high. x, iron bars, called the catch pins, fixed horizontally through the upper part of each arch-head of the working beam to strike the floor and prevent the beam descending too low, in case the chains at either end should break, or if the engine makes too long a stroke. y y, two strong wooden springs to weaken the blow given by the catch-pins when the stroke is too long. z s, friction-wheels or sectors, on which the gudgeons or centres of the great beam are supported; they are the third or fourth part of a circle, and move a little each way as the beam vibrates; their use is to diminish the friction of the axis, which, being necessarily very large for so heavy a lever, would otherwise be very great.