Pumps - Classifications

Pumps are in general classified as Centrifugal Pumps (or Roto-dynamic pumps) and Positive Displacement Pumps.

Centrifugal Pumps (Roto-dynamic pumps)

Centrifugal or roto-dynamic pumps produce a head and a flow by increasing the velocity of the liquid through the machine with the help of a rotating vane impeller. They include radial, axial and mixed flow units.

Types of Centrifugal Pumps:

End suction pumps
In-line pumps
Double suction pumps
Vertical multistage pumps
Horizontal multistage pumps
Submersible pumps
Self-priming pumps
Axial-flow pumps
Regenerative pumps

Positive Displacement Pumps

Positive displacement pumps operate by alternating filling a cavity and then displacing a given volume of liquid. They deliver a constant volume of liquid for each cycle independent of discharge pressure or head.

Types of Positive Displacement Pumps:

Reciprocating pumps: piston, plunger, and diaphragm
Power pumps
Steam pumps
Rotary pumps: gear, lobe, screw, vane, regenerative (peripheral), and progressive cavity

Characteristic	Centrifugal Pump	Positive Displacement Pump
Flow Rate & Pressure Head	Varying flow depending on system pressure or head	More or less constant flow regardless of system pressure or head
Pressure Generated	Lower pressure	Generally makes more pressure
Effect of Viscosity on Flow	Flow is reduced when viscosity is increased	Flow is increased when viscosity is increased
Suitability for Viscosity	Becomes very inefficient at even modest viscosity	Better suited for higher viscosity applications
System Pressure Effect	May have dramatic effect on flow rate	Little or no effect on flow rate
Mechanical Efficiency	Affected by system pressure changes	Less affected by system pressure changes
NPSH Variation	Varies as function of flow determined by pressure	Varies as function of flow determined by speed

Characteristic

Centrifugal Pump

Positive Displacement Pump

Flow Rate & Pressure Head

Varying flow depending on system pressure or head

More or less constant flow regardless of system pressure or head

Pressure Generated

Lower pressure

Generally makes more pressure

Effect of Viscosity on Flow

Flow is reduced when viscosity is increased

Flow is increased when viscosity is increased

Suitability for Viscosity

Becomes very inefficient at even modest viscosity

Better suited for higher viscosity applications

System Pressure Effect

May have dramatic effect on flow rate

Little or no effect on flow rate

Mechanical Efficiency

Affected by system pressure changes

Less affected by system pressure changes

NPSH Variation

Varies as function of flow determined by pressure

Varies as function of flow determined by speed