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Demand pump runs for 20 minutes!

Posted by Lyn347 (My Page) on
Sun, Apr 15, 12 at 10:58

I have a rain harvesting system, which means I collect rain water off my roof for drinking purposes. Yes, I have it filtered to the Nth degree, and it has a UV filtration unit as well. My problem is that recently the centrifigual pump (Grundfos MQ3-45) started running for long periods of time (20+ minutes) and the pressure varies. I have no leaks around the house, and the pressure tank (WellXtrol WX203) varies from 20 psi to 50 psi. When I shut off the system to just the pump and filtering system, the pump shuts off after 20 seconds. Open it back up to the pressure tank and it runs forever. Also, I can shut off the house piping after the tank, and there is no change. So, it seems to me I have some sort of pressure tank problem. Can someone help me with this?

Follow-Up Postings:

RE: Demand pump runs for 20 minutes!

Sounds like a pressure tank that has lost its air charge.

Air above the water (sometimes separated from the water with a rubber membrane) is what stores the energy the pump creates to allow the water to flow out of the pressure tank without the pump running.

Since water is not compressible to anything like the degree of air the air is used to store the energy.

RE: Demand pump runs for 20 minutes!

Thanks for the response. I have set the air pressure on the tank at both 36 psi for 40 psi head pressure on the pump as well as 25 psi to see if a lower pressure inside the tank would make a difference. It didn't. It always measures where I left it last. I don't see it being a lost air charge because of this. Also, I have tried to see if any water comes out when I lower the pressure using the schrader valve, but none does. I am baffled. Also I realize that I need to adjust the internal pressure when the tank is empty.

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