Understanding Pump Types: Dynamic vs Positive Displacement

Understanding Pump Types: Dynamic vs Positive Displacement

Pumps are essential mechanical devices that move fluids from one place to another by converting mechanical energy into hydraulic energy. They are generally classified into two major categories based on their working principle: Dynamic Pumps and Positive Displacement Pumps.

1. Dynamic Pumps

Dynamic pumps add energy to the fluid continuously through a rotating impeller or rotor, increasing the fluid’s velocity and converting it into pressure energy.

a) Centrifugal Pump

Fluid enters the impeller eye and is accelerated outward through the impeller vanes. The velocity energy is then converted into pressure energy in the diffuser or casing.
Applications: Water supply, irrigation, cooling systems, industrial processes.

b) Axial Flow Pump

Fluid flows parallel to the pump shaft (axially). The impeller resembles a propeller, producing lift similar to an aircraft wing.
Applications: Flood control, circulation, and condenser cooling systems.

c) Mixed Flow Pump

Combines both radial and axial flow characteristics. Used when moderate head and high flow are required.
Applications: Drainage, irrigation, and chemical process systems.

2. Positive Displacement Pumps

Positive displacement pumps move a fixed volume of fluid per cycle by trapping it in a cavity and forcing it from the inlet to the outlet. They deliver constant flow regardless of pressure (within design limits).

a) Reciprocating Pumps (Linear Motion)

Use a piston, plunger, or diaphragm that moves back and forth in a cylinder. Each stroke draws in and discharges fluid.
Examples: Piston pump, plunger pump, diaphragm pump.
Applications: High-pressure, low-flow operations like hydraulic systems, oil wells, and chemical dosing.

b) Rotary Pumps (Rotary Motion)

Use rotating elements to trap fluid and move it from the suction side to the discharge side.
Examples: Gear pump, screw pump, vane pump, lobe pump.
Applications: Lubrication, fuel transfer, and viscous fluid handling.

Summary Table