Why Does a Self-Priming Pump Lose Prime During Operation?

Author: Jake Spence | October 11, 2016 | Category: Pumps, Pump Piping

Gorman Rupp Self-Priming PumpSelf-priming pumps are designed to lift water from below the pump’s mounted location. One of the benefits to a self-priming pump is that it doesn’t require you to fill the suction piping with liquid first. If you tried that with a pump that was losing prime, or a regular centrifugal pump, you’d get a horribly choppy flow of water and air. So, what should you troubleshoot if your self-priming pump starts to lose prime during operation?

The first step is to understand the mechanics of a self-priming pump. If you’re unfamiliar, watch this quick 3-minute video that illustrates how a Gorman-Rupp self-priming pump works.

It is important to know that just because self-priming pumps can pull up fluid, doesn’t mean they can run dry. Just like most other pumps, self-priming pumps need fluid in the casing before starting. If you were to run it dry, it will cause damage to the mechanical seal or cause pump failure.

Why A Self-Primer Loses Prime


There are a variety of ways that the suction line can spring a leak. Most of the times this line is underground or in a hard to reach area, so the leak can go unseen. This is the first thing you should check if you’re experiencing priming issues.

A wastewater facility in Door County, Wisconsin was having priming issues that they couldn’t diagnose. They reached out to our service department who came out to inspect their equipment. Upon arrival, we found a suction pipe that would rub on metal grading every time the pump started. Over time, this wore down the pipe until it began to leak. Our service technicians were able to patch the leak quickly and affordably to get them up and running again.


If you watched the Gorman-Rupp demonstration video above, you probably noticed how important the flap valve is. If this valve becomes stuck, your pump won’t be able to prime efficiently. It could also crack or wear out, causing a poor seal. If you’ve verified the suction piping to be in good condition, your next step should be inspecting the flap valve.


It isn’t uncommon for self-priming pumps to be used in pits that might have debris or other small solids. If something gets sucked up and clogs the piping or pump, you will experience poor flow. This isn’t as easy to diagnose as a crack or leak, but should be checked if you’re having priming problems.

If you are in Wisconsin or Upper Michigan and can’t diagnose your pump priming problems, contact us. We’ll help troubleshoot and get your pump back in service. 

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Jake Spence

Jake Spence

Jake is a member of the blogging team at Crane Engineering. He likes to get out in the field and talk to customers about how they've overcome challenges in their facilities, then write case studies to share with others who may face the same challenges.

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