Pumps are devices that move fluids from one point to another. There are two main types of pumps: positive displacement pumps and centrifugal pumps. Each type has its own working principle, advantages, and disadvantages. In this article, we will compare and contrast these two types of pumps and explain when to use which.
Working Principle
- Positive displacement pumps work by trapping a fixed volume of fluid in a cavity and then forcing it out through the discharge port. The flow rate is determined by the speed of the pump and the size of the cavity. The pressure is independent of the flow rate and depends on the resistance of the system.
- Centrifugal pumps work by transferring the kinetic energy of the motor to the fluid through a rotating impeller. The fluid gains velocity and pressure as it moves from the center to the edge of the impeller. The flow rate is determined by the pressure difference between the inlet and the outlet of the pump. The pressure is dependent on the flow rate and the characteristics of the impeller.
Performance Comparison
The following table summarizes the main performance differences between positive displacement pumps and centrifugal pumps.
Table
| Factor | Positive Displacement Pump | Centrifugal Pump |
|---|---|---|
| Flow rate | Constant with changing pressure | Varies with changing pressure |
| Viscosity | Handles high viscosity fluids well | Handles low viscosity fluids well |
| Efficiency | Less affected by pressure | Peaks at a specific pressure |
| Suction lift | Can create suction lift | Cannot create suction lift |
| Shearing | Low shear, suitable for sensitive fluids | High shear, unsuitable for sensitive fluids |
Application Examples
- Positive displacement pumps are suitable for applications that require high pressure, low flow rate, high viscosity, or suction lift. Some examples are metering, dosing, injection, lubrication, and hydraulic systems.
- Centrifugal pumps are suitable for applications that require low pressure, high flow rate, low viscosity, or no suction lift. Some examples are water supply, irrigation, cooling, heating, and drainage systems.
