10 All Too Common Mistakes We See With Self Priming/Centrifugal Pumps - Part 2

by Eric Lunsford
October 10, 2016

Recently I wrote about 5 categories of problems we see when we are called out about centrifugal pumps.

Today I’m going to go through the remaining 5 categories of problems we see all too often with centrifugal pump installations.

Centrifugal Pump Mistake #6: Pipe size and pump geometry mistakes

Centrifugal pumps are the exception to the rule about pipe size – experienced pump users know they need a suction line to be one size larger than the pump suction… Not for self-priming pumps.

The bigger pipe means there will be more air in the line – which means you have longer waits for the pump to prime.

You need to make sure that the suction pipe never goes above the pump’s suction inlet. Any piping above the inlet is a place for air/other non condensable gases to collect… which can bind the suction line.

Centrifugal Pump Mistake #7: Freeze damage.

Any time the temperature drops below freezing for more than an hour or more there is a risk any water in the pump will solidify. When water (unlike most liquids) freezes it expands, which can cause the casing to crack – an unnecessary expense and a big one too.

When there is a risk of freezing nights, either drain the fluid out of the pump or supply a heat source when the ambient temperature is predicted to fall below freezing.

Centrifugal Pump Mistake #8: Running your centrifugal pump backwards.

When centrifugal pumps run in reverse (by accident or by design), the impeller may eventually come loose and damage the pump. Backward-running impellers generally only create about 50 percent of the rated flow and only generate about 50 percent of the rated head.

If your pump is under-performing check to see it is running in the right direction. It’s far less embarrassing when you figure it out yourself rather than place a service call, and our techs come out to they tell you it’s being installed backwards.

Centrifugal Pump Mistake #9: Forgetting Flex pipe normally has a reduced internal diameter.

Using Non-collapsible flex piping is a convenient form of piping when you need a portable pump unit. However, the internal diameter (ID) of flex pipe is smaller than the same sized standard pipe.

This means you need to recalculate the pipe friction for the NPSHA and make sure your flex piping is strong enough to withstand the suction.

Centrifugal Pump Mistake #10: Variable Submergence and

By calculating NPSHA you know the minimum operating level your sump needs to be and can spot air binding risks more easily.

For example, if the fluid is 160 degrees F, the vapor pressure of the fluid alone will likely preclude you from this application. For example, water at 160 F has a vapor pressure that equates to a negative 11 feet.

If the sump you are drawing from will likely have constantly changing levels, at some level of submergence it will be possible for the system to create a vortex and air bind the pump. Even if the pump is not completely air bound, performance can still be affected.

Knowing NPSHA means you’ll be able to keep enough liquid in the sump to avoid air binding your pump.

If you are having trouble with your centrifugal pumps give Pye-Barker a call at 404-363-6000 or drop us a line sales@pyebarker.com we can help you troubleshoot your centrifugal pumps or help you select the right replacement if that is the best course of action.



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