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I’m trying to debug some funny sounds in my shower (just purchased the house containing the shower) and would like to better understand how the plumbing works. The shower is a stand-in type with no tub.

I can visibly trace cold and hot water pipes into my shower ceiling and then down into the wall containing the shower valve. The cold and hot pipes enter the shower valve fitting (which is four feet from the floor). From there, I assume opening the shower valve lets water flow up into the pipe that supplies the shower head (which is 6.5 feet from the floor).
This is my question. When I shut off the shower valve, there must still be about 2.5 feet of pipe (this is the pipe that joins the shower valve to the shower head) containing water. Does that water remain there until the next opening of the valve forces new water into the pipe pushing the old water out through the shower head?

Is there some sort of relief valve that drains that pipe of the water?

Background - After a shower, for about three minutes, I can hear drops somewhere in the wall that contains the shower valve and I am trying to find the source. I’ve opened up the wall behind the shower and all pipes and fittings are dry.

EDIT: The source of noise was my Culligan filter shower head. I removed the shower head and the noise disappeared. Thanks to all for the ideas.

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    Try listening after running only the cold water to the shower, and then after only running the hot water. In my house, some hot water pipes "tick" as they heat up and cool down (probably because they run through a too-tight clearance hole or perhaps a hanger). – mike65535 Aug 13 at 11:12
  • Agree with @mike65535 . Certainly try to check for the existence of water where you don't want it (or sooner or later it'll come thru the ceiling downstairs), but more often than not those sounds are pipe expansion rubbing against supports or clamps. – Carl Witthoft Aug 13 at 18:39
  • the sound could be from the shower drain – jsotola Aug 13 at 21:54
  • Isn't this the same principle as Coke staying in your straw when you dip the straw in the Coke, plug the end with a finger, then lift out the straw? The Coke stays in the straw. – BillDOe Aug 15 at 21:33
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As far as I know there aren't any return valves in these shower systems.

You will have a column of standing water remaining in the pipe.
(When the shower isn't used for a couple of weeks you should always run the water a few minutes before using the shower to get that stale water flushed out. It is an ideal place for bacteria to develop. In hot weather just a week is long enough for Legionella to develop.)

If the pipes and fittings are dry the drip is coming from somewhere else. Noise traveling along pipes can do strange things and it is quite possible the noise comes from somewhere else. It may not even be a drip you are hearing but something similar that you interpret as a dripping noise. (Hot water pipe or the boiler cooling down and making a ticking noise comes to mind. This can sound like a drip.)

What I have encountered myself:
After the shower is shut off that pipe filled with water going up to the shower-head cools off. Cooling causes it to shrink slightly (how much and how fast depends on the pipes material and the ambient temperature) forcing a little bit of water out of the pipe into the shower head.
That water then drips from the shower-head to the floor. Dropping with a noticeable sound on the basin below. (Often people don't notice this drip as the basin is wet anyway after the shower.)
Or, if there remains some standing water in the shower-head itself, it drips into that little pool inside the shower-head. Sound-transfer/amplification will do the rest.
This sort of dripping typically starts 3-5 minutes after the water is shut off and stops after some time (typically another 3 to 5 minutes) when an equilibrium is reached in the pipe.

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    I'm fairly sure this is absolutely nothing to do with contraction of the pipe. It's far more likely to be surface tension keeping the water contained until evaporation at the nozzle reduces the level (and therefore increase the surface area) to where surface tension can no longer contain the liquid, and it drips out. – SiHa Aug 13 at 9:04
  • @siha You could be right. Regardless what exactly causes it the end result is the same. For the record: I've got my shower against the exterior wall. In winter that wall is nearly freezing. Pipes do cool down quick. Evaporation isn't that much of a factor around here but could be in other parts of the world. – Tonny Aug 13 at 9:45
  • It occurred to me this morning, that, because my supply lines come from the ceiling, the noise might be air bubbles in the shower valve that are returning to the supply pipes. Just a thought. Anyway, I'll try the suggestions given and report back if I have any success. – redbeard1 Aug 13 at 17:15

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