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Fluids in Motion

Lift Pump. — Water for household or farm purposes is usually lifted out of moderately deep wells by a lift pump. This pump (Figure 31a) consists of a cylinder that is connected to a pipe S. The lower end of the pipe S is immersed in the water in the well. At the bottom of the cylinder there is a valve В that opens upward. A plunger P which contains a valve A opening upward is moved up and down in the cyl­inder by means of a pump handle. The valve В in the cylinder pre­vents any water above it from passing downward. As the handle is forced downward, the plunger is raised with the valve A closed. The water above the plunger is thus raised and flows out of the spout. The upward stroke of the piston reduces the pressure in the space be­low the plunger. The reduction of the pressure in this space allows the pressure of the air on the water in the well to force more water up the pipe S, through the valve B, into the cylinder. When the piston makes its next downward stroke, the valve В closes, and the water above the valve is trapped in the cylinder. During the downward stroke the valve A in the piston opens and the water flows above the piston. The upward stroke is again repeated and the water flows out of the spout as before. In order that the pump may operate, the valve В must not be more than 30 ft above the surface of the water in the well.

Force Pump. — In the force pump (Figure 31b) the suction pipe S with its valve A is just like this portion of the lift pump. An outlet pipe with a valve В is con­nected to the lower part of the cylinder. As the piston moves downward, the water in the cylinder is forced through the valve В into the delivery pipe D. Raising the piston allows the valve A to open and water to be forced through it by the atmospheric pressure on the water in the well. On the down­ward stroke of the piston, this valve closes and the valve in the delivery pipe opens.

↑S ↑S

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