Knocking water pipes
I have a knocking sound in the pipes when certain faucets or appliances are turned on. It happens with 2 out of 3 toilets, one shower, the washer. This is while the water is running (I'm assuming not a water hammer). When the washer is started, I can turn on a faucet in the downstairs bathroom adjacent to the laundry room and it will stop. We have turned off the main and drained the system (including the sprinkler system and outside faucets) and this worked for one day. Any ideas? When we drained the system should we have left the faucets open when we turned the system back on? Any help will be appreciated.:)
You are correct that the knocking sound while the water is running is not water hammer. Water hammer occurs when a valve is suddenly closed and the momentum of the water traveling in the pipe is brought to a sudden halt. It will result in a bang or, series of bangs with the first one being loudest and tapering off in volume with each successive one.
Your noise could be caused by a number of things...
A very common cause is a loose washer on a valve supplying a number of fixtures. It can be quite loud almost like a jack hammer noise as the washer moves back and forth in the flow of the water.
Some toilet fill valves can also make this noise with a leaking flapper as the valve rapidly opens and closes replenishing the leaking water. The Korky fill valves are somewhat notorious for this....
Sometimes too things like pressure reducing valves on your incoming supply line from a municipal water supply can make this noise and if you are on a well the well pump system can make a knocking noise.
What type of water supply do you have?
Does this noise happen on all fixtures and on both hot and cold or, can your isolate further what causes the noise?
We are on city water and as near as I can tell it doesn't matter whether hot or cold - toilet is all cold, right? Shower when first turned on is all hot, washer is usually cold to warm, so both. This stopped all by itself for a while but now it is back and sometimes it seems that the pipes are coming out of the wall.
I would look at valves common to all those fixtures as possibly being the problem or at the individual points of use as well.
Do you have a pressure reducing valve on your water supply line?
It would look somewhat like the picture below...
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