Centrifugal Pumps vs. Positive Displacement Pumps
Selecting the proper pump begins by knowing
- Total head or pressure against which it must operate
- Desired flow rate
- Suction lift
- Fluid characteristics (temperature, corrosiveness, etc.)
The piping system and pump interact to determine the operating point of pumps: flow rate and pressure.
| Basic Comparison - Centrifugal Pumps Vs. Positive Displacement Pumps |
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|---|---|---|
| Centrifugal | Positive Displacement | |
| Mechanics | Imparts velocity to the liquid resulting in a pressure at the outlet (pressure is created and flow results). | Captures confined amounts of liquid and transfers it from the suction to the discharge port (flow is created and pressure results). |
| Performance | Flow varies with changing pressure. | Flow is constant with changing pressure. |
| Viscosity | Efficiency decreases with increasing viscosity due to frictional losses inside the pump (typically not used on viscosities abov e850 cSt). | Efficiency increases with increasing viscosity. |
| Efficiency | Efficiency peaks at best-efficiency-point. At higher or lower pressures, efficiency decreases. | Efficiency increases with increasing pressure. |
| Inlet Conditions | Liquid must be in the pump to create a pressure differential. A dry pump will not prime on its own. | Negative pressure is created at the inlet port. A dry pump will prime on its own. |
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