Water Hammer

The expert's at JLC sent me here with this question!!!

Any Idea how to stop water hammer from a sump pump? It has 1 1/2" ABS that runs from the sump throough the floor trusses and terminates outside.

On Wednesday the plumber took out the check valve (only a 3/4" flapper) and the sound of 15' of 1 1/2" pipe draining back into the basket was louder than the hammer.

On Friday they put in a FULL 1 1/2" check valve and when the pump stoped it had a quiet "thump". Everyone thought that was OK.

Now, Monday the water hammer will last a good 6 or 7 seconds when it stops. NOT GOOD!

By the way, 2/3 of the pipe is in a finished ceiling.

Any Idea?

From what I hear, look for a check valve with a floating ball rather than a flap. Tends to close quieter and last longer. If the pipe isn't anchored well, that will create problems. Sounds like the new check valve is partially open, and it is taking that long for all of the water to drain back out. All it did was slow it down, not stop it.

I have a similar issue. My main sump pump is a Zoeller Model 98. It's a little overkill but I don't mind spending extra on things like sump pumps. All was working well with my system. I had just the Zoeller pump with a check valve.

This weekend, I added the Basement Watchdog (1/2 HP Big Dog AC/DC) DC battery & AC backup system. To do this I had to Wye off my 1.5" PVC to the 2nd pump and add a 2nd checkvalve (per the instructions). I also replaced the checkvalve on the Zoeller so both valves would be the same size/length. Both check valves are below the Wye connection. Now, when my Zoeller cycles, at the end of the cycle I hear a clunk that I never heard when I didn't have the backup pump installed.

Any idea how I can get rid of the clunk? I assume it's water hammer? Or, maybe the Zoeller is causing some syphon action out of the Watchdog branch of the wye connection creating an air pocket in there or something?

Clocker, try this http://forums.jlconline.com/forums/forumdisplay.php?f=2 it is answers to the same question at JLC.

I'm not sure about your set up, however, I fixed my problem by trying the easiest fix first, figured it would have been the cheapest replacement if it did not work.

I drilled an 1/8" hole in the pipe between the pump and check valve so when the pump stops pumping it stops the pressure of the water and drains to the hole with NO MORE HAMMER! Make sure the direction of the hole points down because when the pump runs water does spray back into the sump basket.

Simple fix!

I just ended up putting back in the old Flotec checkvalve I had purchased from Home Depot. It is silent compared to the checkvalve purchased from Lowes. I didn't think it would make a difference but I figured I better try it since that was my cheapest option.

Both are the rubber flapper type you install with hose clamps. However, just by shaking them, you can tell the Flotec check valve flapper does not flap as freely as the one in the checkvalve from Lowes. I guess it will close faster making it more likely to hammer.

Moral of my story is that the Flotec valve is better! Glad I didn't have to mess with getting one of those ball check valves and hoping that would work...

BTW, my Model 98 Zoeller has an integrated 1/8" weep hole (purpose is to prevent air lock) so I already had that covered.

Thanks for your feedback.

Clocker