Priming the pump

Problem: Pumps with large-volume suction lines that run above the fluid level are often difficult to prime.
By Staff September 1, 1998

Problem: Pumps with large-volume suction lines that run above the fluid level are often difficult to prime. The problem results from the large amount of air that must run through the pump, plus the requirement to lift the fluid from the reservoir into the suction line. Simply filling the pump with fluid is not enough, and the suction line cannot be filled because it drains back into the reservoir. A foot valve is often undesirable or unavailable. Is there another way around this problem?

Solution: Install a port (1/4-in. pipe) at the highest point on the suction line, and attach a small venturi with plant air flowing through it. Open the valve in the pipe. Air flowing through the venturi creates a vacuum at the highest point and draws the fluid into the line until all air is evacuated. At this point, fluid begins to flow out the hose attached to the venturi exhaust, along with plant air. Close the valve in the pipe. The suction line and pump are now full of fluid. Compressed air is disconnected from the venturi, and the pump started.

Contributor: John R. Giegel, PE, Plant Mechanical Engineer, Werner Co., Greenville, PA; 724-588-2000 x 2439