Expert: Dan Griffin - 4/9/2008

Question
When my sump pump shuts off, it makes a knocking sound (2 or 3 knocks) I just replaced the check valve and put it where the manufacturer of the pump suggested. I put it near the pump itself and put a 1/8 inch whole below it for air relief like they said. The pipes are solidly attached and the house is only 5 years old. It is still making the sound. Is there something else I can do?

Thank you!!

Answer
YOu have checked that the noise is check valve related I'm sure, but I don't understand the multiple knocks.  Is your check valve installed hard or with rubber connectors?  Perhaps the noise is exaggerated by hard piping.

Mark,  it surprises me that the flapper makes that much noise.  Most are plastic and rubber and I've not noticed substantial noise, but others must because Graingers offers a special quiet one:
http://www.grainger.com/Grainger/items/1XHV8

I assume you kept the check valve as close as possible to the sump and the air lock hole fairly close to the pump.  Is the check valve in the vertical position or horizontal?  Either should work just fine, but I prefer the vertical position.

I wish I could be more helpful.