Water hammer in system on start-up

[Don H]

After not flowing water overnight I get a water hammer when the pump kicks in. A new pump and hardware was installed in 2018. There is a check valve in the pump, another on top of the pump and a third CV just prior to the pressure tank.

I've researched here and it seems the CV at the tank is not recommended. Could this be causing the water hammer?

 

[Valveman]

After not flowing water overnight I get a water hammer when the pump kicks in. A new pump and hardware was installed in 2018. There is a check valve in the pump, another on top of the pump and a third CV just prior to the pressure tank.

I've researched here and it seems the CV at the tank is not recommended. Could this be causing the water hammer?

Yep.

 

[Sponsor]

 

[Valveman]

The check valve at the tank is what causes the water hammer. But cycling on and off, which also slams the check valve(s) closed over and over is what wears them out to start with.

 

[Don H]

Follow-up: I removed the guts from the CV at the tank and the water hammer has stopped. Hopefully the problem is solved!

 

[Valveman]

Instead of just removing the guts of the CV, replace it with a CSV1A and you will have solved several other problems as well. Just so happens the place where that second check valve should not be, is usually the perfect place and length to install a Cycle Stop Valve.

CSV1A CYCLE STOP VALVE

Compare to the Competition Model CSV1A CYCLE STOP VALVE is recommended for 1 to 25 gpm and is adjustable from 15 psi to 150 psi. It is a stainless steel valve with a molded thermoplastic spring cage. It also has three additional ports (2 - 1/2" and 1- 3/4") and can be used as a pressure tank...

cyclestopvalves.com

 

[2stupid2fixit]

You solved the problem by removing the extra check valve. I studied the physics behind this and multiple check valves along the same line will only fight for equilibrium... vacuum forces at play. In any well setup, its an unnecessary battle. You want the pump to push water to its final place of use. Check valves after the pump will only create air gaps, which make sputtering and water hammer. Even the most perfectly installed systems will have some point to let in air, which can only make headaches.

 

[Sarg]

Just as Valveman suggests.

 

[Valveman]

You solved the problem by removing the extra check valve. I studied the physics behind this and multiple check valves along the same line will only fight for equilibrium... vacuum forces at play. In any well setup, its an unnecessary battle. You want the pump to push water to its final place of use. Check valves after the pump will only create air gaps, which make sputtering and water hammer. Even the most perfectly installed systems will have some point to let in air, which can only make headaches.

Exactly! Now you only have the problem of the one check valve on the pump that is needed slamming shut from the wide open position every time the pump stops. Adding a CSV makes the tank fill at 1 GPM, which means the check valve is also in the 1 GPM position or only open about as much as the thickness of a piece of paper when the pump shuts off. This mechanical soft stop from the CSV eliminates the water hammer as well as damage to the check valve.