The strength of the pump casing and the internal components. In my schools I seldom talk about positive displacement pumps because, unlike centrifugal pumps, there is very little you can do to modify them to increase their performance. They are basically a spare parts business where the performance of the pump is directly related to how well you maintain their internal clearances. In other words, if you were an expert in rotary pumps it is still a parts replacing business, and you know how to do that without having to go through any special training. However, if you are going to be called upon to solve a specific pumping problem, you are going to need a basic knowledge of these pumps because they represent a percentage of the pumps used by the process industry and present the same sealing problems as their centrifugal cousins.
Rotary pumps come in various configurations.
In this paper we will leave out the reciprocating type of PD pump and address the rotary version only. You should know that there are several different rotary configurations being offered to industry. If you are unfamiliar with some of these designs, almost any pump book has pictures of most of them. The centrifugal pump curve shape is determined by the specific speed or shape of the impeller. The centrifugal pump application engineer is charged with the responsibility of matching the system curve requirements with the pump curve.