The most basic classification criterion for differentiating the pumps, whether it is for purpose of analysis or for commercial purpose, is the fluid flow pattern. There are also other important classifications based on the power rating range and fluid discharge rate. The flow supplied by a pump can be intermittent or continuous. The pumps with intermittent flow are all positive displacement pumps and pumps with continuous flow are all Roto-Dynamic pumps. These classifications of the pumps does not end here, these two broad categories have further different types of pumps having varying characteristics. To sum up the classification criterion:
Broad categories based on Flow Pattern:
- Intermittent – Positive Displacement Pumps
- Continuous – Roto-Dynamic or Turbo Pumps
Positive Displacement Pumps
Positive displacement, as the name suggests, is displacing something positively, that is, certain fixed quantity is displaced. In case of the fluid pumps that “something" is fluid for sure. Positive displacement of a fluid is that a closed volume of the fluid is moved from one part of the machine to the other part. The construction of the positive displacement pumps is such that the moving parts along with the fixed ones inside it can form moving enclosed volumes. They open on one side, take the fluid, enclose it and open on the other side, discharging the fluid.
Positive Displacement pumps can further be classified under subcategories according to the motion pattern of the enclosed volume forming parts.
Reciprocating Positive Displacement Pumps
In the reciprocating positive displacement pumps the moving part forming the enclosed volume for fluid displacement has a reciprocating motion. Reciprocating pumps are mainly of two types based on the reciprocating part.
- Piston Pump
- Diaphragm Pump
Each type of these reciprocating pumps is available with various different features. Different variants of positive displacement pumps reciprocating pump are single discharge, double discharge, duplex and triplex.
Rotary Positive Displacement Pumps
Rotating positive displacement pumps have rotating parts which form the moving cavity for carrying the fluid from one side and discharging it at the supply side. Rotary positive displacement pumps are of mainly two types based on the number of rotors.
- Single Rotor
- Multiple Rotor
Each of these two types of Rotary Positive Displacement Pump has pumps available with different design features. Screw Pumps and Gear Pumps are most common Rotary Positive Displacement Pumps.
Roto-Dynamic or Turbo Pumps
Roto-Dynamic or Turbo Pumps are similar in construction as the Hydraulic Turbines just the functioning is opposite to them. Turbo Pumps has rotating impellers with blades or vanes fixed to a rotating shaft. The flow is continuous through the Turbo Pumps. Like turbines turbo pumps are also mainly of two types based on flow direction.
Axial Flow Pumps
The coming articles on fluid pumps will provide information about each type of pumps their construction, working and different features.