How does a bathtub/shower diverter valve work?

[barryj]

TL;DR

This is a water flow issue that I do not understand. How does the tub diverter work.

As we know, when we turn on a tub/shower combo the water initially starts to flow out the tub faucet. When the lever is raised, the water is diverted to the upper shower head. How does this work?

I have learned that the tub faucet lever merely blocks off the water from coming out of the faucet. Since there is a tee where the water source splits between the tub and the shower the water can go either way, it seems to me. When the valve is opened, why does the water go to the tub and not to the shower?

Obviously, if the tub faucet is blocked, the water will be pushed up to the shower head but initially, it seems to me that water will try to come from both the shower head and the tub faucet. What is going on here? Yes, I have googled this question with no answer so far.

 

[hmmm27]

initially, it seems to me that water will try to come from both the shower head and the tub faucet

Not really, but the initial flow, as well as going out the tub faucet, will push some water partially up the shower pipe (which will push air which will push any water still in the shower head onto the occupant, who screams and curses).

A bathtub/shower diverter valve is a plumbing device that allows you to switch the flow of water between the bathtub faucet and the showerhead. It works by controlling the direction of water flow, so you can choose whether you want the water to flow from the bathtub spout or the showerhead.

Here's how a typical bathtub/shower diverter valve works:

1. Three-Way Diverter Valve: In most setups, the diverter valve is a three-way valve, which means it has three ports or openings. These are usually labeled "C," "B," and "S," which stand for "Common," "Bathtub," and "Shower," respectively.
2. Default Position: In the default or "off" position, water flows from the bathtub faucet, and this is the position the valve is usually in when not in use.
3. Changing Flow to the Showerhead: When you want to take a shower, you need to redirect the water flow to the showerhead. To do this, you typically pull up on a diverter knob or lever. This action causes the valve to switch, redirecting the water from the bathtub spout to the showerhead. The common port connects to the showerhead, blocking the flow to the bathtub spout.
4. Adjusting Water Temperature: Some diverter valves also have temperature control features that allow you to set the desired water temperature for your shower. This may involve a separate handle or knob on the valve for adjusting the temperature.
5. Reverting to the Bathtub: After your shower, you can push the diverter knob or lever back down to its default position. This reopens the flow to the bathtub spout, allowing you to use the bathtub faucet again. The water flow returns to the default position when you turn off the water.
6. Variable Designs: While the basic operation is the same, the appearance and design of diverter valves can vary. Some use a knob, while others use a lever, button, or push-pull mechanism.

It's important to note that diverter valves are commonly used in combination with a standard bathtub/shower faucet. In this setup, you have a single handle or knob for controlling water flow and temperature, and a separate diverter mechanism for selecting the flow between the bathtub and shower. This allows for convenient switching between a bath and a shower without needing to adjust the temperature each time.

Diverter valves are essential components of bathtub/shower fixtures, ensuring that water is directed to the appropriate outlet according to your preferences.

 

[DaveC426913]

Why would water rise up to the shower head when there's nothing preventing it from pouring out the tub faucet? What would make that pressure head of three feet?

 

[Nugatory]

TL;DR Summary: This is a water flow issue that I do not understand. How does the tub diverter work.

Obviously, if the tub faucet is blocked, the water will be pushed up to the shower head but initially, it seems to me that water will try to come from both the shower head and the tub faucet. What is going on here?

The diameter of the spout downstream of the diverter is sufficient to carry the entire flow of water from the supply line, and then some. So when the diverter is open, the water level in the vertical pipe to the shower head can’t rise above the top of the spout - if it did, more water would flow out through the spout than in from the supply, bringing the the level down again.

The other trick is that the diverter is designed in such a way that once it is positioned to block the spout, water pressure will hold it there. That’s why after you lift it to start the shower it stays that way, and you have to push it down to get the tub flowing again (and also why when you shut the water off it drops back into the spout position)

It’s a clever design, getting a lot of useful behavior out of very few very simple moving parts.

 

[barryj]

I was thinking that there will be some pressure at the tee and some water would be forced up. Maybe the pressure would not be enough to get all the way to the shower head.

 

[barryj]

I did this experiment. I used a water hose and 3/4 inch PVC as in the following figure.
As expected, the water always flowed out of the down pipe, unless the down pipe is blocked and then it goes through the upper pipe.

 

[DaveC426913]

I was thinking that there will be some pressure at the tee and some water would be forced up.

Nug's first paragraph, above, explains why this is not so.

 

[hmmm27]

The weight of the water above the junction is equal to the "weight", of the tubspout wall drag plus backpressure from the usual 90deg angle in same. It's not negligible : I think house mains typically come in at like 80psi.

 

[jack action]

You should look up "stacking leak" to help you understand. I found these helpful:

• What is a Stacking Leak?
• Water dripping from shower head
• Water comes out of the shower head when faucet is in tub fill mode (I know why, but not how to fix)