A well pump sucks water out of the well and lifts it to ground level for irrigating agricultural fields or supplying potable water to buildings through pipes. Priming means making the water pump fittings air free. Well pump prime losses occur due to defective foot valves, check valves or pipe leaks. Without prime, the pump will run, but the water delivery stops or low water pressure ensues.

A common shallow well pump.

Shallow Well Jet Pump

Install a foot valve or a check valve in a shallow jet well pump's suction line to maintain prime longer. Remove prime reducing air or gases from the pump. To do this, shut the pump's control valve after filling the pump casing and suction line with water, and run the pump, keeping its priming plug loose. This process expels trapped air inside the pump. Repeat the process until smooth water flows around the prime plug, and precharge the pressure tank.

One or Two Line Well Pumps

Priming can be accomplished without removing rusty pump plumbing fittings, especially a corroded pump priming casing plug. This prevents accidental breakage and saves subsequent replacement costs. For this, connect a garden hose labeled "lead free and safe for drinking water," to the neighboring building's outdoor hose connection. Flush out the hose by running the donor building's water through it. Connect the hose's other end to a water faucet near the prime deficient well pump. Open the recipient building water shutoff valve, which will first expel air out of the recipient building faucet and then water will flow through it. Shut the faucet to raise pump pressure to 40 psi. Turn off the water tap connections at either hose ends. Switch on the pump motor. If the pump turns on, pumps water and switches off by itself and building tap water flow is restored, the priming is successfully complete; otherwise repeat the process.

Self-priming Centrifugal Pumps

Self-priming surface centrifugal pumps meant for shallow wells can reprime themselves in about five minutes when they become filled with air, by sending a charge of water into the prime casing. This water and the air from the suction line are drawn into the rotating impeller created vacuum, the air water mixture is sent into the air separation compartment where the air is expelled from the pump and the water is directed back to the priming casing.

Self-priming Submersible Pumps

Use self-priming submersible pumps in deep wells where centrifugal surface pumps are impractical. Priming or replacing the air filled in the impeller region of the pump with water is not an issue in these pumps designed to function submerged in water. The pump's turbulent turbine action ensures the impeller area is flooded and prevents air entrapment within.

Priming Equipment

If you have multiple centrifugal pumps to prime in an industrial or agricultural setting, you can use an automatic or manually controlled vacuum priming system. This apparatus creates a pressure differential in the pump's suction line and pulls water up the line until it reaches the priming valve thereby displacing pump air. The valve will then automatically shut off and the water level control switch will signal the completion of the priming.