Submersible well pump delay and water hammer at cut in

[Larry Grenon]

Installed a new 3/4 hp submersible pump in our well to replace old one. When the pressure drops to cut in 30psi, the relay switch clicks on and there is a 1-3 second delay before the pressure starts increasing, and a water hammer clunk sound at the pressure tank. There is a built in check valve on the pump in the well (some 150' down) and a check valve just before the pressure tank. Oddly, when I run a hose or the sprinkler system, there is no delay or hammer noise, it all works normal. It happens primarily after toilet flushing. The pressure switch seems to work perfectly (30-50) and the pressure tank is 28psi. Please help.

 

[Reach4]

You could try disabling (removing the innards or removing check valve) the above-ground check valve. If the pressure holds pretty well, your water hammer should go away.

If the check valve on the pump is failed, you might have to have the pump pulled and a check valve installed right above the pump.

 

[Sponsor]

 

[Larry Grenon]

You could try disabling (removing the innards or removing check valve) the above-ground check valve. If the pressure holds pretty well, your water hammer should go away.

If the check valve on the pump is failed, you might have to have the pump pulled and a check valve installed right above the pump.

The pump has a built in check valve, and installed last summer. Hard to believe it failed already. I disconnected the line from the above ground cv and the water did drain down the line toward the well pump. I think the line looses pressure down the line due to a leak and when the pump starts, it takes a few seconds to reach the cv in the basement, and the the hammer occurs. Any other thoughts out there?

 

[Midriller]

The stock check valves in pumps are garbage. Reach is on the right track IMO. Pull any surface check valves and see if it drains back.

 

[Reach4]

The pump has a built in check valve, and installed last summer. Hard to believe it failed already. I disconnected the line from the above ground cv and the water did drain down the line toward the well pump. I think the line looses pressure down the line due to a leak and when the pump starts, it takes a few seconds to reach the cv in the basement, and the the hammer occurs. Any other thoughts out there?

It's possible that the leak is at the pitless adapter or elsewhere on the path. 1 inch ID pipe is
0.041 gal/ft of pipe. If your pump puts out 15 gpm, that is 0.25 gal/sec from the pump. If those are the right numbers and I calculated right, that could mean that the leak could only be about 18 to 2o ft away for a 3 second delay to bang.

Check my math and assumptions. I may have messed this up. The result of my calculations surprised me. Plug in the actual ID of your pipe if you like.

 

[Larry Grenon]

The stock check valves in pumps are garbage. Reach is on the right track IMO. Pull any surface check valves and see if it drains back.

I did disconnect the pipe from the surface cv, and the water did drain toward the pump, leading me to believe there is a bad cv or leak in the well pipe, and that causes the delay and hammer. What else could it be?

 

[Larry Grenon]

It's possible that the leak is at the pitless adapter or elsewhere on the path. 1 inch ID pipe is
0.041 gal/ft of pipe. If your pump puts out 15 gpm, that is 0.25 gal/sec from the pump. If those are the right numbers and I calculated right, that could mean that the leak could only be about 18 to 2o ft away for a 3 second delay to bang.

Check my math and assumptions. I may have messed this up. The result of my calculations surprised me. Plug in the actual ID of your pipe if you like.

I will check the pitless for leak, but if it is leaking, wouldn't air enter the pipe to replace the water leaking out? I have seen no air coming out the faucets to indicate air entering the line.

 

[Reach4]

I will check the pitless for leak, but if it is leaking, wouldn't air enter the pipe to replace the water leaking out? I have seen no air coming out the faucets to indicate air entering the line.

Very good point. Flaw in my thinking.

What is your static water level?

 

[Valveman]

I agree it is a bad check at the pump. Hole in pipe would cause air in the lines. Some check valves are better than others, but they all fail because of too much pump cycling. Pounding a check valve closed 50 to 100 times per day every time the pump cycles off is hard on check valves. Reducing the number of pump cycles and causing a soft stop like when using a Cycle Stop Valve will make even cheaply built check valves last longer.

 

[Larry Grenon]

Removed the check valve near pressure tank and the pressure held steady, so there is no leak in the line to the pump. The water hammer is gone. Success!

 

[Reach4]

Removed the check valve near pressure tank and the pressure held steady, so there is no leak in the line to the pump. The water hammer is gone. Success!

The fact that the pressure tank could then apply a little pressure may have made the check valve in the pump seal better.

 

[Valveman]

The fact that the pressure tank could then apply a little pressure may have made the check valve in the pump seal better.

Yep! Check valves always seal better when they have all the pressure on them instead of just weight from the drop pipe.