Centrifugal pumps are designed to pump liquids not gases. Any centrifugal pump (even a self-priming pump) will not start pumping unless at least the first stage (such as in a multistage vertical pump) is full of liquid. When pumping a liquid with an excessive amount of entrained air, the air/gas tends to be centrifuged inward towards the eye of the impeller, eventually blocking any liquid flow through the pump (air binding it). If this only happens occasionally, the pump has a positive suction pressure (flooded suction), and the flow stoppage can be quickly detected, stopping and restarting the pump can clear up the air binding.
However, if the pump must pull a lift, or could over heat from the flow stoppage, one (or a combination of) the following system design changes should be considered:
1. Add a foot valve in the suction line, so that the pump will remain flooded when the pump is stopped, however, foot valves can leak over time.
2. Attach a small self-priming pump to the discharge side of the primary pump, and operate it when the main pump looses prime, to remove any air in the primary pump and suction piping.
3. Install a water ejector to the pump discharge pipe, to prime the pump when necessary.
4. Replace the above ground pump with a vertical turbine, sump or submersible pump, where the pump (at least the first stage) is flooded at all times. This may require creating a pit or sump.
5. Replace the above ground pump with a self-priming pump capable of handling the total flow requirement. The efficiency of a self-priming pump will, however, be typically lower than for its non-self-priming counterpart, due to the additional liquid turns and close impeller/casing volute tongue clearance in a water-primed self-priming pump. The energy required to drive a separate vacuum pump, or compressor, for air/vacuum-primed pumps, must also be taken into account in the efficiency evaluation.
Changsha Zoomlian Pump Co., Ltd, established in 1989, is an enterprise which engages in the production and sales of multistage pumps, centrifugal pumps, single stage pumps, inline pumps, split case pumps, sewage pumps, submersible pumps, fire pumps, oil pumps, irrigation pumps, chemical pumps, boiler feed pumps etc. Our products have a good reputation in the domestic and foreign markets covering the fields of energy, mining, metallurgy, petroleum, chemical industry, building materials, textiles, food, marine development, national defence construction, urban construction etc.
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