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Wayne Model 605 Gas Pump Photographs: By substituting the value of torque from the previous equation, the basic relation for head in a centrifugal Pump is found to be:by the Pump is always less than H' due to frictional losses within the pump. The Pump efficiency E is the ratio of the head impressed to the head delivered, thus :For very large pumps efficiencies above 90 per cent have been obtained; in general, efficiencies decrease as the size of the Pump decreases.
A widely used arrangement for farm water supply systems consists of a combination of a centrifugal Pump and a jet Pump as shown in Fig. 15. The centrifugal Pump furnishing the driving head and water to create the jet. Because of the entrainment principle more water flows up the vertical pipe than is delivered by the jet. Among the advantages of the centrifugal-jet Pump combination is the accessible location of the centrifugal Pump and motor on the ground surface and the fact that there are no moving parts in the well. Under favorable conditions the capacity of the centrifugal Pump is such that approximately 50 per cent of the total discharge is returned to supply the jet.
The total head produced by this Pump is the sum of the heads developed by the individual impellers. A second basic type of radial Pump is the equivalent of parallel operation of two identical pumps. In this type of pump, known as the double-suction pump, the impellers are again placed back to back on the same shaft. However, the casing is constructed so that water enters both impellers from the common suction pipe and the flow from both runners discharges into the same volute chamber. In the double-suction Pump the total flow rate is twice that of a single-suction pump, but the head produced is the same. A single-stage, double-suction Pump is shown in Fig. 11. |
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