Is a check valve needed??

I'm replacing the pressure tank in my mom's house. The well has a submersible pump. Should there be a check valve on the pump or do I need to put one just before the tank? Would it cause problems to put a check valve before the tank anyway? I don't know what is there now and have no way of finding out before I make the trip up there. Thanks.

There should be a check valve in the pump and having one by the tank can be a problem for several reasons.

bob...

Thanks Bob.

Bob,

Can you elaborate on what the problems of putting a check valve just before the pressure tank (i.e. downstream from the pump, but upstream of the tank) might be?

Thanks,
DSK

Valveman

Multiple check valves are no problem as long as they are both working like new. The problem happens when the bottom check leaks back a little bit, (even a couple of thimbles of water) and the top check is holding perfectly. This is like putting your finger on top of a straw full of water. The water will not drop out of the bottom but it is at a negative pressure between the two checks. Still have positive pressure above the top check. So when the pump starts, the pressure between the two checks changes from negative to positve instantly and you hear a thump. That thump is water hammer and it puts 10 times the normal pressure on you pipe and system. So if your pump delivers 100 PSI (231' of head), when you hear the thump, the pipe leaving the pump sees a 1000 PSI pressure for an instant. In a water well situation the pipe and pump actually try to jump out of the well when this happens. If you only have a check at the bottom, the pipe is always under positive pressure when the pump starts and no water hammer.

Another reason is: Let's say the check valve in the well is leaking, the one at the tank is holding fine. Now you have a vacuum on the entire string of pipe from the check valve at the tank to the pump. So there is a little leak in a coupling in the horizontal line from the tanks check valve and the well. The dog has just left his duty on the lawn, it's raining hard, the ground is getting all wet around that coupling, the duty is melting the coupling is drawing a vacuum... you get the picture.

bob...

Yup, and here in Hillsborough County Florida, the plumbing inspector who the well drillers and pump guys fall under "this year" has deemed it necessary to make it mandatory to install a check valve and union at the top of each new well and pump installation. I argued with him until I was blue in the face and he insisted it was a good idea. Go figure.

They always know more than the guys actually doing the work.

bob...

Thanks for the great explanations and anecdotes. Wish I'd known this sooner. The submersible pump I installed in my well does have a check valve built into the top of it. But not knowing what I know now, I ordered the Tank Tee package at this link, including the check valve:
http://www.do-it-yourself-pumps.com/pressure-tank-fitting-kit.htm

Guess I won't need that check valve after all...

Unless there's somewhere else in my water system that it might come in handy.

DSK

It would make a nice paper weight.

bob...