How Well Pumps Work
There are above ground and submersible well pumps with many variations of both, but typically a submersible pump is physically down in the well and PUSHES the water up and out of the well. The above ground shallow water pump works through suction, with atmospheric pressure doing the real work. Because suction is involved, atmospheric pressure is what’s really doing the work. Think of the system as a long straw. As you suck on the straw, you create a vacuum in the straw above the water. Once the vacuum is there, the weight of the air, or the atmospheric pressure, pushes the water up the straw. Consequently, the height that you can lift the water with a shallow-well jet pump relates to the weight of the air. While air pressure varies with elevation, it’s common to limit the depth of a shallow well to about 25 feet. Sketch of Double Acting Positive Displacement Pump
Note the 4 valves and their orientation.
It’s a DOUBLE ACTING because it pumps on BOTH strokes of the piston. It’s POSITIVE DISPLACEMENT because the piston displaces a fixed volume of water.
Reciprocating Pumps- Definition & Overview

 

By definition, a reciprocating pump is any machine using reciprocating motion to cause fluid to be moved from one location to another. The most common form of reciprocating pump is the positive displacement type.
Figure 1
This type of pump traps a fixed volume (Figure 1) of fluid and displaces it from suction conditions to discharge conditions by means of check valves placed in series, at least one on the suction side and at least one on the discharge side. These check valves ensure fluid movement is in one direction from pump suction toward the pump discharge. Since a fixed volume of fluid is displaced the rate of flow is directly proportional to speed. Capacity can also be increased by using a pump with multiple plungers or pistons. Pump speed and number of plungers/ pistons available is limited by mechanical considerations. As a result of the fixed displaced volume per pump revolution and the fact that pressure is independent of pump speed and flow rate, there is no capacity-head curve for these machines as with centrifugal pumps. If a capacity curve were to be drawn, it would simply be a straight line from zero capacity and speed to maximum capacity and speed, like shown in Figure 2 at 100% (theoretical) volumetric efficiency and another line at actual application volumetric efficiency. Piping should be laid out so no high points occur where vapor pockets may form. Vapor pockets reduce the effective flow area of the pipe and consequently make pump priming and operation difficult. Vent any unavoidable high points and provide gauge and drain connections adjacent to pump. Figure 2 Fig 1&2: Herber H. Tackett, Jr.; James A. Cripe; Gary Dyson
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