Pumps move fluids through nearly every industrial process, from water treatment to chemical dosing. The two main families are centrifugal pumps and positive displacement (PD) pumps, and understanding their differences prevents costly mismatches.
How Centrifugal Pumps Work
A centrifugal pump uses a rotating impeller to add velocity to the fluid, which is then converted into pressure. Flow varies with system pressure, which makes these pumps ideal for high-volume, low-viscosity liquids such as water, light solvents, and cooling fluids. They are simple, compact, and relatively inexpensive.
How Positive Displacement Pumps Work
PD pumps trap a fixed volume of fluid and force it into the discharge. Examples include gear, screw, lobe, diaphragm, and piston pumps. Flow stays nearly constant regardless of pressure, so they handle viscous fluids, shear-sensitive products, and precise metering tasks well.
Selection Considerations
- Viscosity: efficiency of centrifugal pumps drops sharply as viscosity rises.
- Flow and pressure: centrifugal pumps suit high flow at moderate head; PD pumps suit lower flow at high pressure.
- Solids and abrasives: choose designs and materials that tolerate the fluid.
- Net positive suction head (NPSH): verify available NPSH exceeds the pump's requirement to avoid cavitation.
Never throttle a PD pump discharge without a relief valve, as pressure can rise until something fails. For centrifugal pumps, operating far from the best efficiency point causes vibration, seal wear, and wasted energy. Reviewing the pump curve against the real system curve is the most reliable way to size either type correctly.