2010-01-12 - Hot water in my shower

I was taking a shower and I noticed the water was too hot. I turned it down. Something I do every day- but how the hell does it work? I knew there was some sort of valve back there mixing hot and cold water and maintaining pressure. I use it every day and I don't know exactly how it works- I think I'm going to investigate a lot of stuff like this.

Gotta start somewhere- I won't go as far as the water treatment plant but lets start when the water comes into the building. This is easy for residential applications but when you start getting into buildings that are more than 5 stories tall it gets a bit more involved.

So the water comes in and for the cold water it's pretty straightforward. That gets pushed through the whole house just from water pressure from the source. The cold water also flows into the water heater where it is heated (electric, gas, oil). The tank is really just an extension of the line so the water pressure going into it is what you get out of it. The cold water enters the tank at the bottom and mixes in. The hot water rises to the top of the tank and is drawn from the top. When you run out of hot water that means the water level is too low for the pipe to draw anything out of it.

So now you've got your hot and cold water flowing to the shower with equal pressure. Mixing the two manually is pretty easy. Two knobs- one for each line- open each valve until you get the mix you want. So how do the single handle mixers in showers work? What kind of valve is in there?

So on a faucet for a sink this is a pretty typical arrangement. Front and back for on and off- and then the hot and cold water lines flow in on the sides. Push to the left- open the right. Push to the right- open the left. Push straight back and you open both the hot and cold equally to get a neutral mix. In the ones I could find it's a pretty neat spring plate/ball valve assembly to open and close the valves. For the shower it's a little different anatomy.

I couldn't find any diagrams anywhere to confirm my thoughts so here's the best I can do- if anyone knows for sure let me know.

When you start to turn the the valve it opens up the cold line first. I imagine there is some sort of drive screw so as you turn it out away from the wall it probably reveals the inlet for the cold water first. As you turn it further it gradually opens up the inlet for the hot water and mixes it. It makes sense- but it doesn't mean it's true. If anyone knows for sure how it works, let me know.