The engine will thus continue to raise water four or five hours, till both the guage pipes N and 0 give steam, which shows that the boiler requires a supply of water.
In order to replenish the boiler, turn From you the handle K behind L, which will bring the notch 7 of the key in Fig. 2, to the situation in the right hand sec tion in Fig. 2, and then the cocks M and Y being still open, the water will flow from the cistern through the forcing pipe and steam pipe into the boiler without going into the receiver, the steelyard being off the valve, and the cock 0 open to let out the air as the water enters. Whenever the cock 0 ceases to blow, and the valve descends, turn back the handle to K, and shut the cock Y.
Some of Dr. Desaguliers' engines were erected after 1717-1718, and one of them was for the Czar, Peter I. for his garden at St. Petersburg. The water was drawn up by suction 29 feet high, and then forced up 11 feet higher. In another the water was drawn up 29 feet, and forced up 24 feet higher.
Various engines on the principle of Mr. Savory's have been erected since his time, and various improve ments have been made on the original construction; and as there are many circumstances under which they may still be advantageously employed, we shall describe one which was erected by Mr. P. Keir at St. Pancras, and which was employed for many years to turn lathes, Ste. The following description of it is given by Mr. Keir himself in Nicholson's Philosophical Journal.
The figure, Plate DV, Fig. 3, is a section of the engine, taken through the centre. B represents a boiler, shaped like a wagon, seven feet long, five feet wide, and five deep: it was considered as being of di mensions sufficient to work a larger engine ; a cir cumstance which must, in a certain degree, diminish the effects of the present one. The boiler feeds itself with water from an elevated cistern, by a pipe which descends into the boiler, and has a valve in it, at the upper end, which shuts downwards, and is connected by a wire with a float on the surface of the water within the boiler, so as to open the valve whenever the water subsides below the intended level ; for the float which swims on the water then sinks, and by its weight draws the valve up, to allow the water from the cistern to run down the pipe and supply the den, ciency : but as the water in the boiler rises the float closes the valve. The boiler therefore remains con
stantly or nearly at the same degree of fulness.
The steam is conveyed by a pipe C to a box D through which, by the opening and shutting of a valve it can be admitted to the cylindrical receiver A. The axis K serves as a key to open and shut the valve, which is a circular plate, formed conical on the edge, and fits in a corresponding aperture in the bottom of the box D. H is a cistern from which the engine draws its water through a vertical suction pipe, in which a valve, G, is placed to prevent the return of the water. R is another cistern into which the water is delivered from the receiver A, through the spout F, which is provided with a valve opening outwards. '\VW represents an overshot water wheel eighteen feet in diameter, of which the axis S communicates motion to the latches and other machines used in the manufactory.
The engine raises the water from the lower cistern H, by suction, into the receiver A, from which it runs into the upper cistern R, and thence flows through a sluice into the buckets of the water-wheel W to give it motion. The water, as it is discharged from the buckets of the wheel, falls again into the lower cistern H. As the same water circulates continually in both the cisterns, it becomes warmer than the hand after working a short time; for which reason the injection water is forced up by a small forcing pump from a well. This injection pump is worked by the water wheel, by means of a loaded lever, or pump handle, which is raised up by the motion of the wheel, and then left to descend suddenly by its weight, and force up the water into the receiver. A leaden pipe passes from this forcing pump to the upper or conical part of the receiver A, for the purpose of injecting cold water at the proper time. Neither of these could be represented with convenience in the present section.