296

DESCRIPTION OF ENGINE.

In the engraving marked SMEATON, Fig. 1, is an elevation of the self-regulating apparatus, or handgear. Fig. 2, is a plan, or horizontal section, of the same mechanism. Fig. 3, a section of the sliding valve, through which the steam was admitted from the boiler into the cylinder. Fig. 4, section of the bottom of the cylinder. In all the figures the same letter is placed on the same part. a, is a part of the cylinder; d, a part of the plugframe; e, injection water-pipe; f, pipe conveying steam from the boiler into the cylinder, and at the bottom of which the valve shewn in Fig. 3, is placed; i, injection cock; k, forked lever which opens and shuts it; 7, another forked lever for opening the sliding valve on the steam-pipe, which is marked o; m, a catch communicating with the cataract; r, tumbling bob of the injection cock; s, tumbling bob of the steam-pipe valve. These weights perform the same office in this apparatus that they have already been described to perform in Newcomen's early engines.

The operation of this machine is nearly the same with others which have been already described. In the figures the parts are in the position they would occupy if the piston were at the top of the cylinder, (which is filled with steam,) and the steam and injection cocks were shut, and the apparatus ready to act as soon as the cup of the cataract is filled with water. At the instant this is accomplished it falls to one side, and makes the bent lever 5 draw up the chain ≈ of the catch m, and the prong a being disengaged, the weight or tumbling bob r impels the prong 1 on the lever 2, and during its movement into the opposite position opens the injection cock i. The jet condenses the steam beneath the piston, which, fall

2

IRREGULARITY OF ACTION.

297

ing into the cylinder, performs its working stroke; at the same time the tappet-framed descends, and when near the termination of its motion, a pin 6, striking on the arm y, opens the steam valve, and at the same instant another tappet shuts the injection cock; the counterpoise now draws the piston to the top of the cylinder, and when it is about to reach the limit of its returning stroke another pin in the plug frame moves the y piece, and the steam valve is again shut. The cylinder is now filled with steam, and remains so until the cataract cup inclines to one side, when the fall of the tumbling-bob r again opens the injection cock and the piston descends as before.

There were also several extraneous circumstances which produced irregularity in the mechanism, even when the steam power was made to act with great uniformity. In all the machines which have been described, the weight of water, or other load which the engine had to raise, has been considered to be equal and constant. But in the greater number of instances in which steam power was employed, the water which had to be drawn from a mine, did not accumulate with regularity. The operation itself of pumping the water which had accumulated, varied the load on the pumps; and when, from any cause, the water suddenly fell in the cistern, and air found its way under the pump-barrel, if the piston were working with its usual load, its descent destroyed the apparatus. The general rate of the motion of the piston, might be perfectly regular, and from time to time be regulated by decreasing the load on the piston, by making a less perfect vacuum, or by admitting more or less water into the cylinder; but this required so much care on the part of the attendants, and such

disastrous consequences ensued when it was omitted, that it was rarely resorted to; an obvious and simple, but not very economical method was preferred. Where the situation permitted, the water was allowed to accumulate beneath to a certain extent, and the engine was then put in operation to pump a certain portion of it to the surface; it then ceased working until a second accumulation had taken place, and so on constantly.

A better method was to keep the machinery always in action, and to regulate the engine so that it should make only a certain number of strokes in a minute, and thus allow time for a fresh accumulation between each stroke. The cataract, a well known contrivance for this purpose, was used by Smeaton, and also in many cases by Watt.

A small pipe, a, which proceeds from a cistern c, is furnished with a cock, d, to regulate the size of the stream of water which falls from it into a funnel, e; this funnel is placed over a cup fixed on the end of a bent lever, f, g, that moves on an axis, h; a chain or wire, i, is fixed to one end of this lever, the other end of the wire is attached to a spanner or catch, which acts by its rise or fall to engage or disengage a lever that opens the cock of the injection-pipe. The cup and bent lever are placed in a box, through the bottom of which the chain proceeds; a small pipe, k, carries off any water that may fall on the bottom. It is first found from trial, how often a certain stream will fill the cup the required number of times each minute, and the cock is adjusted accordingly. The water then which falls into the funnel, is guided into the small cup, and when it is filled, the weight of the water makes it fall over, and turns the opposite end of the bent

lever on its axis, and the chain fixed to it raises the end of the catch, which acts to open the injection valve; and this condensing the steam, the engine makes a stroke, and the counterweight lifts the piston into its former position, as has already been described in the Chacewater engine.

During this operation, the water from the cup is emptied into the box and carried off by the pipe, and the chain, acting as a counterweight, quickly restores it to its position under the funnel, and the stream of water filling the cup again, it a second time falls to one side, the engine makes another stroke, and so on successively. It is obvious, that as the stream of water is made more or less, a greater or less time will be required to fill the cup, and of course a greater or less number of times will the injection cock be opened, and the piston make its stroke.

Another plan practised by the old engineers, was still retained in many situations, to ascertain the depth of water in the pit, in order to guide the engine-keeper to regulate the movement of the machine, and to avoid the accident of water failing in the pump, when working with its usual load.

An iron pipe, perforated with holes at its bottom, was placed in the cistern of the mine; a wooden cylinder (having a projecting piece of iron fastened to its under side) made smaller than the diameter of the pipe, so as to move easily up and down, floated on the surface of the water in the pipe. A cord was attached to this float which passed through a hole in the cover of the pipe, and was carried up the pit shaft and guided over a pulley into the engine-house, where it passed over a second pulley, and was terminated by a small weight, hung within reach of the en

300

MINE GAUGE.

gine-keeper. By pulling this cord, he could always tell whether the water stood high in the cylinder, or was nearly exhausted. In the first case the float was buoyant, and in the other, when the float was raised by the rope it fell, and the piece of iron coming strongly in contact with the iron bottom of the pipe, gave the information that was desired; and by a little practice, he could also distinguish whether the float was nearly at the top of the pipe, which it would be, when the cistern was filled with water. Watt sometimes used this contrivance with a modification, which better adapted it to his practice, and he made it regulate the working of the engine. Instead of a rope, a strong wire was attached to the float, and this was connected to the lever which opened and shut the injection cock and the passage for steam into the cylinder. The fall of the float was made to diminish the opening for the steam, and its rise to open the valve; and in some instances, it was also made to regulate the cock of the cataract-pipe, so as to allow a greater quantity of water to escape into the cup when the float rose, and thus by filling it oftener, increase the number of strokes made by the steam-piston. The fall of the float to the very bottom of the pipe, either shut the steam-passage or the cataract cock, and thus the accidents which would have befallen the apparatus from a failure of water in the pumps were prevented, as the motion of the engine ceased entirely.

It is probable Smeaton was also the author of the warning-gauge; for it first appeared in engines which he constructed, and he made it serve as well for a gauge and feeding-pipe. A pipe inserted through the roof of the boiler, was