POSITIVE DISPLACEMENT PUMPSDOE-HDBK-1018/1-93PumpsRotaryMovingVanePumpThe rotary moving vane pump shown in Figure 19 is another type of positive displacementpump used. The pump consists of a cylindrically bored housing with a suction inlet on oneside and a discharge outlet on the other. A cylindrically shaped rotor with a diametersmaller than the cylinder is driven about an axis placed above the centerline of the cylinder.The clearance between rotor and cylinder is small at the top but increases at the bottom.The rotor carries vanes that move in and out as it rotates to maintain sealed spaces betweenthe rotor and the cylinder wall. The vanes trap liquid or gas on the suction side and carryit to the discharge side, where contraction of the space expels it through the discharge line.The vanes may swing on pivots, or they may slide in slots in the rotor. Figure 19 Rotary Moving Vane PumpDiaphragmPumpsDiaphragm pumps are also classified as positive displacement pumps because the diaphragm actsas a limited displacement piston. The pump will function when a diaphragm is forced intoreciprocating motion by mechanical linkage, compressed air, or fluid from a pulsating, externalsource. The pump construction eliminates any contact between the liquid being pumped and thesource of energy. This eliminates the possibility of leakage, which is important when handlingtoxic or very expensive liquids. Disadvantages include limited head and capacity range, and thenecessity of check valves in the suction and discharge nozzles. An example of a diaphragmpump is shown in Figure 20.ME-03Rev. 0Page 26
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