Water hammer, I thought, was heard on abrupty closing valves

[david shapiro]

What's the mechanism? When I open, I say open, an upstairs single-valve sink faucet after it's been closed a minute or more, I hear a thunk. Hot water position, cold position, middle/mix position.

The plumbing upstairs is 1/2 in. CPVC, and the whole system was installed about nine years ago. This does not happen with other faucets: not the tub just upstream, from whose feeds the sink is teed. It does not happen with the other sinks using the same faucet, neither the downstairs one closer to the entrance nor the upstairs one further.

Not a worry, but a source of curiosity.

[Jerry Peck]

Two main possibilities that I can think:

1) A loose, improperly supported and secured, pipe.

2) An anti-water hammer air chamber too small or waterlogged (both are installation problems, created by making shortcuts and/or not doing things properly).

If you can locate the approximate area of the noise, you could probably use a mechanics stethoscope to more precisely locate where the pipe is hitting the wall, stud, whatever. If the location allows for access (hole in wall), you may be able to resecure the pipe, or cushion where it bumps to so as not to make noise and so it doesn't potentially cause damage to the pipe.

[david shapiro]

Thanks, Jerry. Why would inrush cause this: displacing air in the pipe and then hitting a ninety or tee?

[Dom D'Agostino]

I have found the cause to almost always be an unsupported pipe or similar installation issue.

[Jerry Peck]

David, there is no air to be displaced in the system ... hopefully no air on the system.

The sudden movement/flow of the water in the pipes, when not properly supported, can cause movement of the pipes. An unsupported or improperly supported pipe can bump against something, which creates the noise.

[david shapiro]

Thank you.

[Jim Robinson]

If it's your own house, you can sometimes get it to stop by spraying a can of Great Stuff into the wall cavity through a 1/4" hole. That is assuming you know where it is happening. The Great Stuff will expand and sometimes push the pipe against the framing or sheet rock and secure it. That can save on some sheet rock repair depending on the location.

[david shapiro]

Good point, Jim.

It is my own house. The only systems I evaluate for others are electrical.

To zero in on the location, I shall have to recruit my sweetheart to listen as i open and close the faucet. Wifely hearing has not been damaged by decades of power tool use and misuse, layered onto a quarter-century of reliance on a motorcycle as my primary means of transportation.

[ROBERT YOUNG]

The single-valve sink faucet might be the culprit.
Watter hammer or water resonance? They both create banging sounds.
It sounds like you narrowed down the point of the noise. The single-valve sink faucet.
Stop valves, commonly referred to as stopcocks, can cause water hammer if their gland packing is loose and/or they have worn washers.

Here is a link that offers several ways to resolve this banging issues. What?s the Difference Between Water Hammer & Resonance? (https://www.rabielplumbing.com/blog/plumbing/whats-the-difference-between-water-hammer-resonance#:~:text=Water%20hammer%20is%20a%20loud,m ay%20also%20cause%20this%20sound.)

[david shapiro]

Thank you, Robert. The Biel Plumbing link does not mention single-valve faucets in its discussion of resonance, just toilet tanks. Did I end up in the wrong place?

[ROBERT YOUNG]

Thank you, Robert. The Biel Plumbing link does not mention single-valve faucets in its discussion of resonance, just toilet tanks. Did I end up in the wrong place?
No. I only provided 1 link. My ,istake.