Although there are various types of positive displacement pumps the most common amongst these are the rotary,
metering and reciprocating pumps. Although each type of pump serves a particular purpose, the most common objective of positive displacements pumps is to move fluids in hydraulic FIre Hose Testers systems where there is a pressure of up to 500psi. In other words positive displacement pumps generate a very high pressure that is capable enough to move a fixed volume of fluid.
Is there a distinction between the rotary, metering and reciprocating pumps or are they identical in their operation and can be termed as positive displacement pumps?
Broadly speaking each of the three is a positive displacement pump, but is unique in its operations. For instance a reciprocating pump comprises three parts that work in close coordination with each other. These comprise the piston, plunger and the diaphragm. Such pumps are beneficial in those instances where only a small quantity of fluid is to be pumped and the pressure of delivery is very high. In such pumps the fluid gets stored in a chamber that typically comprises a stationary cylinder and the liquid is pushed out via the coordinated movements of the piston, plunger and diaphragm.
On the other hand a rotary pump is a type of positive displacement pump in which there are vertical blades placed on top of a rotor which rotates inside the chamber and generates pressure to move the fluids. The length of the blades depending upon the desired level of contact that is to be established with the walls.
Lastly a metering pump is a type of positive displacement pump that moves a definite volume of fluid in a definite period of time, thereby ensuring that the rate of flow of the liquid is maintained. Typically speaking, apart from pumping water, these pumps are used to pump chemicals, solvents and other types of fluids.
Positive displacement pumps are used mostly in the offshore exploration and oil refinery industry but because of their importance and usage, they are increasingly being used in other industries as well. These industries typically comprise bakery and confectionery industry, pharmaceutical, liquid delivery and processing, food and dairy, chemical processing and manufacturing industry.
Positive displacement pumps are popular because they are very versatile and compact. They are able to render high viscosity performance and ensure continuity in the flow of fluids irrespective of the fact whether there is constant or irregular pressure. Lastly the ability to function under adverse weather conditions is another reason of their popularity. The pumps are usually made of high quality metals that ensure ruggedness and versatility.