Types of Pumps
The family of pumps comprises a large number of types based on application and capabilities. The two major groups of pumps are dynamic and positive displacement.
Dynamic Pumps (Centrifugal Pump)
Centrifugal Pump—Click image to enlarge and view reference.
Centrifugal pumps are classified into three general categories:
Radial flow—a centrifugal pump in which the pressure is developed wholly by centrifugal force.
Mixed flow—a centrifugal pump in which the pressure is developed partly by centrifugal force and partly by the lift of the vanes of the impeller on the liquid.
Axial flow—a centrifugal pump in which the pressure is developed by the propelling or lifting action of the vanes of the impeller on the liquid.
Positive Displacement Pump
Positive Displacement Pump—Click image to enlarge and view reference.
A positive displacement pump has an expanding cavity on the suction side of the pump and a decreasing cavity on the discharge side. Liquid is allowed to flow into the pump as the cavity on the suction side expands and the liquid is forced out of the discharge as the cavity collapses. This principle applies to all types of positive displacement pumps whether the pump is a rotary lobe, gear within a gear, piston, diaphragm, screw, progressing cavity, etc.
A positive displacement pump, unlike a centrifugal pump, will produce the same flow at a given rpm no matter what the discharge pressure is. A positive displacement pump cannot be operated against a closed valve on the discharge side of the pump, i.e., it does not have a shut-off head like a centrifugal pump does. If a positive displacement pump is allowed to operate against a closed discharge valve, it will continue to produce flow which will increase the pressure in the discharge line until either the line bursts or the pump is severely damaged or both.
Types of Positive Displacement Pumps
| Single Rotor | Multiple Rotor |
|---|---|
| Vane | Gear |
| Piston | Lobe |
| Flexible Member | Circumferential Piston |
| Single Screw | Multiple Screw |