Selection of Pumps

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The following factors influence the choice of pump for a particular operation:

1. The quantity of liquid to be handled: This primarily affects the size of the pump and determines whether it is desirable to use a number of pumps in parallel.
2. The head against which the liquid is to be pumped. This will be determined by the difference in pressure, the vertical height of the downstream and upstream reservoirs and by the frictional losses which occur in the delivery line. The suitability of a centrifugal pump and the number of stages required will largely be determined by this factor.
3. The nature of the liquid to be pumped. For a given throughput, the viscosity largely determines the frictional losses and hence the power required. The corrosive nature will determine the material of construction both for the pump and the packing. With suspensions, the clearance in the pump must be large compared with the size of the particles.
4. The nature of power supply. If the pump is to be driven by an electric motor or internal combustion engine, a high-speed centrifugal or rotary pump will be preferred as it can be coupled directly to the motor.
5. If the pump is used only intermittently, corrosion troubles are more likely than with continuous working.

The advantages of reciprocating pumps in general over centrifugal pumps may be summarized as follows:

1. They can be designed for higher heads than centrifugal pumps.
2. They are not subject to air binding, and the suction may be under a pressure less than atmospheric without necessitating special devices for priming.
3. They are more flexible in operation than centrifugal pumps.
4. They operate at nearly constant efficiency over a wide range of flow rates.

The advantages of centrifugal pumps over reciprocating pumps are:

1. The simplest centrifugal pumps are cheaper than the simplest reciprocating pumps.
2. Centrifugal pumps deliver liquid at uniform pressure without shocks or pulsations.
3. They can be directly connected to motor derive without the use of gears or belts.
4. Valves in the discharge line may be completely closed without injuring them.
5. They can handle liquids with large amounts of solids in suspension.

The general result of the above considerations is strongly in favor of the centrifugal pump.