The centrifugal pump is the most used pump type in the world. The principle is simple, well-described and thoroughly tested, and the pump is robust, effective and relatively inexpensive to produce.
Positive displacement pumps, on the other hand, operate by forcing a fixed volume of fluid from the inlet pressure section of the pump into the discharge zone of the pump. Positive-displacement pumps frequently are used in hydraulic systems at pressures ranging up to 5000 psi.
Lobe pump is a type of positive displacement pump that offers superb sanitary qualities, high efficiency, reliability, corrosion resistance, and good clean-in-place and sterilise-in-place (CIP/SIP) characteristics.
Before selecting the right pump for the job, we need to understand:
- 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 | 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 above 850 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. |
If you need assistance with your pump selection, please contact All Pumps today.
