Whenever we run hot water in the kitchen (faucet or dishwasher), a loud knocking noise comes from the PVC pipes in the basement. It seems to be coming from the main drain pipe which is about 3 or 4 inches in diameter, and it knocks right along the ceiling joists. After a few minutes the knocking stops. Any suggestions?
your probably hearing the supply lines knocking against the drain pipe which can eventually lead to a failure in the supply line at a connection point or coupler. have somebody run the watewr while you go downstairs and check for movement in the pvc. if the pvc moves you will need a air hammer arrester, if no movement detected run each faucet individualy and see if the problem is in a valve
Any knocking in water pipes is generally associated with the water hammer effect that results from the sudden changes in pressure within the pipes when a faucet or valve is opened and closed. This may be eliminated by installing a commercial hammer arrestor. The other possible and just as likely of a culprit is a worn out flat washer on a faucet. The flat washer which is generally made of neoprene will wear very thin and begin to flap when running the faucet. If you get the hammering when any faucet is turned on or off it is most likely needing a hammer arrestor. If the problem is localized, or at only an individual faucet it is most likely needing a new valve seat and washer.
Insert some foam rubber between the pipe and joists. I would guess that the noise is from the water supply pipes rather than the drain though. Secure the water lines with metal strapping that has holes in it. If the water lines are plastic, lay a piece of rubber between the pipe and strap to prevent cutting from vibration. Normally this strapping is used for hanging duct work.
it sounds to be a loose system but what you are asking sounds like contraction and expanding from hot water and then it cools off and it goes back to normal, it creeks. its plastic you can insulate it might help
Same as with copper - install an air surge valve
