Pump Types

Food and beverage pumps are divided into two generic types: rotodynamic and positive displacement. Both types are widely used in the food and beverage industries.

Rotodynamic Pumps Rotodynamic (centrifugal) pumps are widely used in hygienic applications (Figure 1) because they are simple and inexpensive, they give a smooth delivery, and they are relatively easy to clean. They are, however, limited by viscosity that will greatly reduce pump efficiency above about 500 centipoise, generally regarded as the limiting viscosity. As the pumps rely on speed of rotation to generate head, there are fairly high shear rates within the pumping elements that affect shear-sensitive products. Also, because it is not self-priming, it has a limited ability to handle entrained gases and vapors. A positive feature of centrifugal pump designs is that the performance varies according to the system operating conditions to which it is subjected. Unlike a positive displacement pump, the discharge of a centrifugal pump can be partially or fully closed without over-pressurizing the pump.

FIGURE 1 Hygienic centrifugal pump (APV Fluid Handling)

advantages These pumps are simple; they are of generally robust construction; pumps are easy to clean in place; pumps cannot be over-pressurized against a closed valve; they can be connected in series for increased pressure; and they can be connected in parallel for increased flow.

disadvantages These pumps typically are not self-priming; they are generally limited to about 500 centipoise viscosity; they are limited ability to handle fluids that are shear-sensitive; and they have a limited ability to handle high percentages of entrained gases.

Positive Displacement Pumps Positive displacement pumps are used in processes where viscosity limits the capabilities of a centrifugal pump or where the process needs to be versatile and the batches vary. They are normally self-priming and can handle gaseous products. However, all positive displacement pumps require pressure relief systems to prevent damage to the pump or system if a valve is closed or the outlet blocked.

Many types of positive displacement pumps are available and they are normally split into two groups—rotary and reciprocating, the reciprocating type needing a valving system to be able to operate. Valves increase shear rates and are susceptible to wear and blockage.

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