Shurflo 4008-101-A65

I haven't ever relied on a mere pump's non return valve. Aftermarket valves are inexpensive and ten times the valve of any water pump's device.

The check valve in the pump will do just fine if it's working. Like any check valve, a piece of debris in it will keep it from sealing. I would take the head apart and rinse everything under water. If it still allows back flow then it's defective.

Thanks for the replies.There is a small allen key adjustment on the by-pass valve.(check valve) I was hoping that someone might know how to adjust that. All I can find is the adjustment for the pressure valve. I guess I could just screw the allen key adjustment in and increase the spring pressure. I already cleaned the internals of the pump. We will see................I'll let you know how it works.

Thanks
Bruce

That model of pump uses a 'bypass' valve to control low flow stutter .......
It begins opening at 40# and is fully open by 62#

If not properly set water WILL backflow thru pump when using city water source

HERE is a down/dirty method for adjusting Main and Bypass settings




Check valve not fully sealing will allow backflow when on city water or when using pump

Many times just using pump will clear and debris holding check valve open.
Full tank...use it and then swap back to city water and see if you still get backflow thru pump

Old-Biscuit wrote:
That model of pump uses a 'bypass' valve to control low flow stutter .......
It begins opening at 40# and is fully open by 62#

If not properly set water WILL backflow thru pump when using city water source

HERE is a down/dirty method for adjusting Main and Bypass settings




Check valve not fully sealing will allow backflow when on city water or when using pump

Many times just using pump will clear and debris holding check valve open.
Full tank...use it and then swap back to city water and see if you still get backflow thru pump

Thank you "Old-Biscuit"this is what I was looking for. The pump is clean and now I will do the adjustment.

Thanks
Bruce