Although water may be raised 34 feet with a theoretically perfect pump and with a barometric pressure of 30 inches the actual limit is much lower. In use, 20 feet is probably about the limit and 10 feet or less is that of common practice. A pump that requires “priming” would raise water 15 feet with considerable difficulty for reasons that will appear later. In Fig. 129 is shown a sectional view of the working parts of the kitchen pump, the action and general form of which apply to any lift pump. The body of the pump contains a cylinder, in which closely fits a piston _P_, containing a valve _A_. At the bottom of the cylinder is an additional valve _B_. The piston and two valves constitute the working parts of the pump. The water is lifted through the pipe _S_, and is discharged at _D_. [Illustration: FIG. 129.--Sectional drawing of the kitchen pump showing its working parts.] The action of the pump is as follows: With the piston at the bottom of the cylinders and with no water in the pump, the handle is forced down, which action raised the piston. In so doing the air below it is rarefied. The reduction of pressure due to the rarefication of the air allows the water to rise in the pipe _S_ correspondingly. After repeated strokes of the piston, the water reaches the valve _B_, which raises to let it pass, but immediately closes at the end of the upward stroke. When the space between the piston and the valve _B_ is filled with water, each descent of the piston forces the water through the valve _A_; and when the piston is raised, the water is lifted out through the spout. The valve _A_ is a loose piece of cast iron, surfaced on the lower side to make good contact with the piston. The valve _B_ is of cast iron fastened to a piece of leather by a screw. The leather makes a joint with the valve-seat and furnishes an excellent valve for its use. In order to keep the plunger _P_ tight in the cylinder, it is surrounded with a leather gasket. Should this gasket become worn, as it will in time, the plunger fits loosely in the cylinder and the pump will lift the water with difficulty, because of the leakage around the gasket. Should the valve _B_ leak, the water will gradually run back into the pipe _S_, and the pump when left idle will lose its “priming.” The plunger and the valve _B_ are the parts most likely to get out of order. If the gasket around the piston _P_ is very much worn, and there is no water in cylinder, the pump will require priming before the water can be raised. If the pump contains no water and is left standing for a considerable time, the leather parts of the valve dry out and shrink; when the pump is again put into use, the valves will fail to work properly, until the leathers are again water-soaked. Water is poured into the top of the pump until the cylinder is filled, and as soon as the leather becomes water-soaked and fills the cylinder, the piston will again perform its function.