Technical

Type of Pumps and Definitions

Positive Displacement Pumps

A Positive Displacement pump is also known as the power pump and it operates by continuously deliver liquid flow but independent of the pressure in the discharge piping  system. The discharge piping system produces resistance to this liquid flow, thereby generating pressure in the discharge piping system. Unlike centrifugal pump, it does not develop pressure but rather produces a flow of liquid.

Positive Displacement pumps can be further divided based on the mode of displacement:

  1. Reciprocating Pumps – works in a transitory dynamic condition called the pumping cycle via linear movement of the plunger or piston. A reciprocating pump makes up of liquid end and power end.
  2. Rotary Pumps – the displacement is by rotating action of gears, screws or vanes in a fixed casing/ chamber. Rotary pumps do not generate pulsation. The inherent high efficiency of a rotary pump makes its design very suitable to handle high viscosity liquid.
Unlike kinetic pumps, all positive displacement pumps can theoretically move the same volume of fluid at a given speed (rpm) no matter how the discharge piping system is setup. Thus, all positive displacement pumps are flow or volume devices. 
Figure 2. Screw Pump Cutout (Credit to CC BY-SA)

Dynamic Pumps

A Dynamic pump is distinguished by the way it operates. It uses a centrifugal force of the rotating impeller to impart kinetic energy to the fluid, moving the fluid from one level of pressure to a higher level of pressure. 

There are several varieties of dynamic pumps and some are classified as follow:

  1. Centrifugal Pumps are the most widely used fluid handling devices in the refining, petrochemical and general industrial applications. Typically, more than 85% of the pumps installed in an industry are centrifugal pumps.
  2. Regenerative Pumps are also sometimes called peripheral pumps. This type of pumps in general produces high head and low flow. It can also handle a certain amount of air or gas in the liquid as long as sufficient liquid remains in the pump casing to seal the clearance between the suction and discharge passages.
  3. Vortex Pumps or recess impeller pumps are designed to handle liquid with solids without clogging the casing passage.
  4. Special Effect Pumps are particularly used for specialized conditions in an industrial service.
All kinetic pumps deliver variable volume of fluid for a constant differential head at a specific flow condition by using rotating impellers or blades to increase fluid velocity. All kinetic pumps are relatively sensitive to pumping liquid properties and to system changes as well.

Let’s Talk About Pumps

What are pumps?

In general, regardless of the type of  pump, it is defined as a mechanical device or equipment that is used to:

  • transfer or move liquid from one point to the other by imparting kinetic and potential energy to the liquid.
  • built up pressure or pressurization purpose.

Pumps can be further classified into two main categories, according to their basic operating principle as detailed below:

  1. By means of dynamic (or kinetic) – in which energy is continuously added to increase the fluid velocities within the pump. Fluid pressure is increased when the fluid velocity is subsequently decreased.
  2. By means of positive displacement – in which energy is periodically added to the fluid by direct application of force to one or more moveable boundaries of any fluid-containing volumes, resulting an increase in pressure up to the value required to move the fluid through ports or valves in the discharge point. 

Figure 1 shows the Types of Pumps we discussed above.

Figure 1. Types of Pumps

Dynamic pumps can be further sub-classified into several varieties of centrifugal, regenerative and other special-effect pumps.

Displacement pumps are essentially classified into rotary and reciprocating types. Each of these classifications can then be further subdivided into several types of variations depending on the nature of service it is designed for.

Figure 1 above also presents an outline summary of the significant classifications and sub-classifications within these categories.