In this pump the pipe A A may be dis pensed with, and the barrel B immersed in the reservoir ; in which case the action of the pump is independent of the atmos pheric pressure, and could be maintained equally well in a vacuum.
In order to produce a continued stream through the pipe G H, an air vessel, ma, may be attached to the late ral branch above the valve F, fig. 3. The pipe G II reaches too near the bottom of the air vessel ; and when the water has been forced into the vessel by the action of the pump, until it reaches above the lower end of the pipe at G, it is evident that, as all communication is then cut off with the external atmosphere, every additional quantity of water thrown into the vessel will tend more and more to compress the air within it, which, acting by its pres sure on the surface of the water, forces it through the pipe G II in a continued stream.
The lifting pump is represented by fig. 4. The barrel of the pump is immersed in the water and fixed to an immovable frame. The piston with its bucket and valve C, opening upwards, is attached at E to another frame, G H I K L, consist ing of two strong iron rods, H I and L K, which move through holes in the frame work to which the pump is fixed. An inclined branch M N, either fixed to the top of the barrel, or movable by means of a ball and socket, is fitted exactly to the barrel, and furnished with a valve at M. Suppose the barrel immersed in the water to a certain depth : if the piston frame be now thrust down by the handle at G, the pis ton will descend, and the wa ter be forced by its upward pressure through the valve C, so as to maintain the level in the pump as in the well. But when the piston frame is elevated, the valve C will shut (as shown in ths figure), and the water above C be lifted up with the piston, and forced through , the valve M into the branch M N from which its return will be prevented by tho shutting of the valve M when the piston descends.
In each of these different kinds of pumps which have been described, the total effort required to work the machine, independently of friction, is equal to the weight of a column of water, the base of which is equal to the area of a section of the working barrel, and the altitude equal to the distance between the surface of the water in the reservoir and the point to which it is raised. In the sucking pump the whole of this effort is expended in raising the piston • in the forcing pump one part is expended in raising and the other in depressing the piston, and it is advantageous to dispose the machinery so that these two parts shall be nearly equal. In small pumps for domestic pur
poses, the strength of man is usually em ployed as the moving power ; but in rais ing water from great depths, as the bot tom of mines, the steam-engine is appli ed to this purpose. (See FIRE ENGINE.) Mr. Von Schmidt, of New-York, has patented a centrifugal pump, which works thus : There are two circular flanges which are bolted together and form a hollow ring, with the sides, like two discs bolted together, forming a hollow cham ber within, and having a wide circular circumferential chamber (hollow ring). There is an orifice of discharge, to which a pipe may be attached, and a pipe for a lower orifice on the other side communi cates, air-tight, with the water in the well, or other place. The shaft runs through the pump, and has a stuffing box to render it air-tight when it passes into and out of the circular chamber, a large pulley aided by a band from any power revolves the arms inside to raise and force the water. The blades of the arms run in the circumference or hollow ring, and the arms revolve between the two sides. The blades are not stuffed nor fitted to run stiffly in the hollow ring, a thing common to other rotary pumps, and which causes much friction, a rapid wear of rubbing surface, and hence con signs them to an early tomb. It is, on the other hand, fitted to run with ease, like a blower ; so that its passages do not get clogged up, and sand, gravel, &c., do not injure it. It requires no inside pack ing; all the parts are simple, easily cast and put together. Pumps of this kind are made capable of discharging from 5 gallons to 5,000 gallons of water per min ute with suction pipe of wrought or cast iron, copper or lead, or flexible pipe of leather or India rubber ; also discharge pipe of iron, copper or lead, and hose of leather, India rubber, or gutta percha. It is both a suction and force pump; and may be used as a fire engine by simply attaching hose to the discharge-pipe : by increasing the power, the quantity of water discharged will increase proportion ately. Its movement being rotary, this increase may be indefinite ; or up to the point of velocity with which water will fill a vacuum. It has been adopted by the United States government in the construction of the Water Battery on Staten Island, harbor of New-York, and at the extensive fortifications now in pro gress on the Tortugas Keys, Florida, and it is useful for almost every hydraulic purpose.