Most centrifugal pump issues happen on the suction side of the pump. Read on to learn about the 10 most common self-priming pump problems.
It needs to be primed before its first operation. Yes, it’s called a self-priming pump but it has to be primed before you use it for the first time. There’s a priming chamber somewhere that will need to be filled before you start it. Read the instruction manual or go online to check for details if you’re not sure. Sometimes the pump might need manual re-priming after the first prime; for instance, if the fluid has evaporated, the pump has moved, or there has been a leak.
It’s too far from the liquid source. You want the pump as close as possible to the suction source. Thirty feet is the max recommended distance and it makes sense to keep the suction pipe length as short as possible to get the most life out of your pump.
The required lift is too high. In a perfect scenario, at sea level, you could lift 65-degree water 34 feet with a self-primer. However, you should probably limit your suction lift to, at most, 25 feet due to things like friction, pump inefficiencies, elevation above sea level, fluid temperature, and specific gravity.
There’s a leak in the suction line. There could be a leak of air into the line so you can put some plastic wrap around the flanges or areas where you suspect a leak to test for ingress leaks. As a general rule, if your pump takes longer than three or four minutes to prime then you should shut it down and look for what is causing the problem.
The suction piping is the wrong size. The suction piping should be the same size as the pump suction because the added air volume means more priming time, which you don’t want in a self-priming pump. You can learn more about the basic rules of pump piping at Crane Engineering.
There’s no air vent and that air has to be vented to an area of lower pressure if the pump is to properly prime.
Check the net positive suction head available. The sump you draw from will probably have operating levels that change constantly. At some value of minimum submergence it could create a vortex and air bind the pump.
The flex pipe was incorrectly applied. Non-collapsible flex piping is usually used on portable units and the inside diameter of flex pipe and adapters are normally smaller than standard pipe. If the ID is too large, or the flex pipes are too old, the pipe ID liner will collapse under vacuum and block the line. If you want to learn more about pump issues, visit the Dynapro website for additional information.
Avoid reverse rotation. If the impeller comes loose it may damage the pump. The backward-running impeller typically will create about half of the rated flow and will generate about half of the rated head. If it’s spinning the wrong way, it probably won’t prime or work properly except for in the simplest of suction lift cases.
Avoid freeze damage. This can happen anywhere the temperature drops below freezing for over an hour. The fluid in the priming chamber of the pump will solidify if the temperature goes under freezing for long enough. When water freezes it expands, and the casing of the pump will crack, which is expensive. To avoid this, you will need to either drain the fluid from the pump or supply a heat source when the temperature is supposed to be below freezing.