Any plumbers here? Whuffo my shower do this?

Something I’ve wondered about for a long time:

After I turn off the shower in the morning, it drips a bit (of course) for maybe a minute or so. The dripping stops. All is well.

About 10 minutes later, however, a deluge of water will suddenly and startlingly come pouring out of the bath nozzle and the shower head at the same time. If I had to estimate the amount of water that comes out, I’d guess it’s probably in the range of a cup total.

What’s up with that?

Obviously water is slowly building up for a few minutes before suddenly releasing, but why? And what triggers this sudden orgasmic release?

(before anyone asks: no, there is no pattern to it that I’ve noticed… no flushing of toilet, etc. that precipitates (ha!) the event…)

Any insight will be much appreciated!

Does your shower have one of those little plunger things on the bath nozzle that redirects water to the shower head? If so, do you push it back down when you’re done showering? I’ve noticed that if I forget to do so, it falls on its own after a bit and water cascades. I guess it (the water) gets stuck in the pipe up to the shower head and then the release of the bath nozzle blockage lets it out…not that I know for sure.

So maybe that’s it? Although I don’t recall water coming out of the shower head when this happened.

Yeah, it does have one of those… but I don’t push it back down after I shower, as we rarely take baths. So I don’t think that’s it. The water comes out of both the showerhead and the nozzle at the same time, which I don’t think would be the case if it was that water diverter dealy.

No, that’s exactly what would happen. When the water diverter returns to the “bath” position, the water in the pipe leading up to the shower head is released, and comes out of the bath nozzle. At the same time, air enters the pipe, which allows the remaining water in the pipe just before the shower head (the pipe which is horizontal, then points down towards the shower head) to spill out of the shower head.

In other words, if you push it back down as soon as your shower is over, you’ll release the water immediately.

Hmmm. That sounds reasonable save one detail: the little plunger thing that I have to push down for water to not come out of the shower head doesn’t fall down. It stays in the up position, and takes an appreciable force to push down (I just ran to the b-room to double check this).

I’m thinking that we might be on the right track here, though. How does the mechanism inside the pipe operate to divert the water? Is it possible that this mechanism is falling open (without the little plunger moving) after a while allowing the water to escape, but then closing again the next time I take a shower? After all, I never have to pull the plunger up to switch the water back to the showerhead in the morning…

That must be what is going on.

Thanks, guys!

Anyone got a link to an example of this diverter thing? I’m having a hard time picturing exactly how this would happen, and don’t know what to call it for a Google search.

I doubt it. You’ve turned the valve off, so no new water should be entering the system. What you do have above the diverter is an inverted U shaped tube that’s full of water after you turn the shower off. The water on one side of the U wants to drain down through the shower head, and the water on the other side wants to drain down through the faucet. Neither side is free to drain because that would create a vacuum at the top of the pipe. The balance between the weight of the water on the two sides of the U isn’t perfect however, and you can get little bubbles of air traveling up the pipe. Sooner or later, you get enough air at the top of the U that water on either side can flow out. It does so with a catastrophic gush and a gurgle.
The same thing can happen with the last bit of liquid trapped inside a siphon.

The spout diverters I’m familiar with work this way: water flows into the tub filler until the lever is lifted. Then, water pressure pushes the seal plate washer tight and water pressure is diverted up the vertical riser and out of the shower head. A minor amount drips from the tub filler.

When you shut off the water flow, the seal is still there, held by the head pressure of the standing water column, until enough water leaks past the diverter seal washer that gravity in the assembly causes the plate and handle to drop, and remaining water in the filler/riser flows out.