Despite what all the engineers and pump salesmen will tell you, there really are only two types of pumps; centrifugal and positive displacement. Understand the difference between these two and you are well on your way to understanding pumps. The difference is that centrifugal pumps spins at a high speed and transfers centrifugal or kinetic energy into the liquid in the form of velocity and pressure. The positive displacement pump, on the other hand, transfers a precise measured amount of liquid from the inlet to the outlet for each rotation or stroke of the pump. Let’s look at each.
A centrifugal pump is the most common pump you will find in a brewery. There are several types of centrifugal pumps; open impeller; multi-stage, liquid ring and submersible are a few of the common ones. The most popular manufacturers of sanitary pumps are Alfa Laval, Ampco, Fristam, Topline and Waukesha.
Most of the centrifugal pumps we see now are close coupled to a C-Face electric motor which greatly reduces the number of parts and simplifies maintenance.
Use a centrifugal pump when you want to transfer liquids with little or no solids content, and you need a high volume and a relatively low pressure. (<100 psi) Positive displacement pumps
There are many different styles of positive displacement (PD) pumps, the most common used in the brewing industry are the positive rotary, the progressive cavity, the flexible impeller and the air operated diaphragm pump.
The positive rotary pump is quite common in a brewery. It has two rotating impellers that turn in opposite directions and trap pockets of product between the lobes and the casing.
Another common PD pump is the flexible impeller pump. The flexible impeller pump is a kind of a hybrid, it has a high speed (relative to a positive rotary) single impeller, like the centrifugal except the impeller is made of a flexible rubber material. The impeller seals tightly against the casing forming pockets for the liquid. These pumps are popular because they are self priming.
Use a PD pump when you want transfer a thick liquid or you have a lot of solids in the liquid. These would be used for pumping mash-in-wort, syrups, liquid sugar or yeast slurry.