A self-priming centrifugal pump has two phases of operation: priming mode and pumping mode.
In its priming mode, the pump essentially acts as a liquid-ring pumpChina Pump controllers manufacturers. The rotating impeller generates a vacuum at the impeller’s ‘eye’ which draws air into the pump from the suction line. At the same time, it also creates a cylindrical ring of liquid on the inside of the pump casing. This effectively forms a gas-tight seal, stopping air returning from the discharge line to the suction line. Air bubbles are trapped in the liquid within the impeller’s vanes and transported to the discharge port. There, the air is expelled and the liquid returns under gravity to the reservoir in the pump housing.
Gradually, liquid rises up the suction line as it is evacuated. This process continues until liquid replaces all the air in the suction piping and the pump. At this stage, the normal pumping mode commences, and liquid is discharged.
When the pump is shut off, the design of the priming chamber (normally involving a ‘goose-neck’ on the suction piping) ensures that enough liquid is retained so that the pump can self-prime on the next occasion it is used. If a pump has not been used for a while, it is important to check for losses from the casing due to leaks or evaporation before starting it.
What is a Compressed Air Self-Priming Pump?
It is possible to use compressed air, instead of a liquid charge, to prime a pump. Compressed air is blown through a jet into a tapered tube to create a vacuum. Air from the pump casing and suction line is drawn in with the compressed air and vented. A check valve seals the discharge line, allowing liquid to enter the pump body. This method has the advantages that the potential for blockages is reduced (because there is no priming chamber) and the pump can be run dry safely.