Plumbing Question

[PMK]

Hi,

I need some expert advice.

My water tank is underground. I did not see the plumbing pipes installed and of course most of them are buried in concrete.

I have a problem with the pump coming on when no water apparently is being used, but for now my question is simply about the installed plumbing.

There are two pipes on the input side of the pump. One has a what I would call a back pressure valve – a simple flap valve, and I assume is the municipal water input. The other does not have a valve. I have no idea what that pipe is for, but if it is shut, then water stops flowing into the house. Again, this is on the input side of the pump. Any ideas on the purpose of that pipe?

Thanks,

Peter