So I was reading instructions on a submersible well pump wich I do because I have been installing them my whole life. I was surprised to learn they wanted a check valve (one way water flow valve) at the pump it self and at ground level or below ground level where the plumbing meets the pressure tank. My question is why two? I have never heard of it and I certainly won't be installing two because I know it's not needed for long life span. I see pumps decades old all the time with only the check valve inside the pump it self. I was just curious why they want that. I'm no scientist but I know there are some in this forum. My only guess is extra protection. I some times install multiples of things like limit switches because there very cheap. Check valves are pretty spendy though. Thanks for any input.

 

Redundancy is the only reason I can think of.

 

I don't have the latest plumbing code book, can not prove my point.
I need to prove that water in pipes can not back flow to the well or to the city supply. My water might have been sitting for a long time and not be safe. Normally I must add a Pressure Vacuum Breaker to stop back flow. In my case I did not want to add this to my system. My other option is to add two Check Valves, because they are not as reliable as a Breaker. A Vacuum Breaker opens if pressure is low or a vacuum is present and also stops back flow, (double action).

The inspector wants to see the two Check Valves. I argued that one Check Valve is at the motor that he could not see. It took a while to talk him into that.

 

A check valve at the surface seems sensible to prevent possible contamination of the water column in the well from some cause at the surface.

 

A second Check-Valve can also "spread-out" the Shock-Loads caused by Water-Hammer.
Water-Hammer can be extremely powerful.
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Belt and suspenders approach it seems. My well system doesn't have any check valves! The submersible pump has it built into it so no external stand-alone one used. IF that one fails you will know it pretty quickly and with multiple ones, how will you even know if one fails? You have a compressed fluid system and any leaks will cause the pump to run non-stop trying to maintain pressure. Bladder tanks help and I find those systems with a submersible pump far better than the alternatives. BTW I never had a check valve failure but am on my 3rd pump and they were still running after 20 years of use for each one. Damaged well point filters tend to suck in sand and eat impellers up a bit even though the motor still runs or the well driller that services our system thought 20 years was long enough and time to retire it (and sell me a pump).

 

BTW I never had a check valve failure but am on my 3rd pump and they were still running after 20 years of use for each one.

The check valve on my well failed. Rather than having to pull up the pump to replace it, I installed one above ground. Before I did that, I spoke with someone who worked on my system and he said that failed check valves were a common occurrence.

A few years before that, they replaced my pump and all of the pipes for a pretty penny and I think the original problem was a failed check valve. They tried to tell me that it was a hole in the pipe and that I should replace my pump at the same time so I didn't have to go to the expense of pulling it up again (something like $600-800 just to pull it up) later, so I did.

Failure in my case has been sediment that prevented the valve from closing. I've had to clear sediment from the check valve I installed a couple times. It was a good thing I decided to install unions on both sides instead of just gluing...

 

Longevity of check valves also depends on the pH of the water in the well. I have a shallow well jet pump with a foot valve in the well and another check valve at the pump. I've replaced the foot valve twice over the 30 years that I've owned the property. With the pH of my water, ~6.9, they last about 15-20 years.

With a submersible pump, having the check valve at the pressure tank relieves the valve at the pump from the full pressure of the tank. What's left is only the water column weight.