PUMP

A machine for raising water. Though the forms under which this useful engine is constructed, and the mode in which the power is applied, may be modified in an infinite number of ways, there are only three which can be considered as differing from each other in principle. These are, the sucking pump, the forcing pump, and the lifting pump, so called from the manner in which they act. The sucking pump, or common household pump, is an apparatus of which the principle and construction will be evident from the annexed figure. A A is a pipe of any convenient length, the lower end of which reaches,.. below the surface of the water in the well or re- ^ 'i servoir; B is a barrel, generally of greater diamter than the pipe; C a valve opening upwards; _, Da piston moved by the rod E: in this piston "J there is also a valve opening upwards. When the piston is raised, the air in the barrel between the valves is expanded, and its tension, consequently, diminished; the pre ure of the air in If the pipe, therefore, opens the valve C, and the whole air in the pipe and barrel becomes le Eb dense. In this state the atmospheric pre ure on the surface of the water causes it to rise in the pipe, until the tension of the confined air becomes On INM equal to the pre ure of the atmosphere. ' again depre ing the piston, the valve in it opens, and the air pa es through it from the bane! as it descends; but the valve C is closed by the downward pre ure, and the volume of water which has entered the pipe remains. On again raising the piston, the same effect is repeated, and an additional quantity of water enters the pipe. Thus, by the alternating motion of the piston, a column of water is raised in the pipe until it reaches the piston when at the bottom of the barrel, and the whole of the air below it has been < v eluded. On raising the piston when the water has reach it, the fluid will be compelled to follow by the pre ure the atmosphere on its surface in the well. When the pu [s. 1016]