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.
Best Answer
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.