Hi - Here's a picture of a Tempress II pressure-balance diverter valve (for use in a tub/shower situation). 

This is similar to what I found recently when called by a homeowner who recently had a shower remodeled.  He purchased a waterfall spout to be used as a showerhead and a separate handshower.  He purchased these on the internet and then went to a local plumbing supplier to purchase the valves to operate the outlets he already owned.  He was sold a pressure-balance valve with a separate diverter.  No, it didn't work.  The waterfall didn't flow; it spit.  What he needed was a thermostatic valve - more on that in Part 3. 

Pressure-balance valves are useful in limited situations.

A pressure-balance valve is just one type of anti-scald valve, required by code in most areas of the United States.

Like any "anti-scald" valve, the pressure-balance valve does not recognize the actual temperature change; instead, it recognizes a reduction in pressure coming from either the cold or the hot water lines. When the pressure is reduced in one of the lines, the valve will reduce the volume of water emitted through the fixture. This reduces the volume to a trickle.

Most pressure-balance valves allow you to control only the temperature and not the volume of water. From the off position, the valve typically rotates counterclockwise from cold to warm to hot. Volume? You get what you get ... unless the valve allows you to control the volume. Be sure to check.

Most of these valves will accommodate 3-7 gallons per minute. A showerhead is required by Federal law to allow only 2.5 gallons per minute at 80 psi or 2.2 gpm at 60 psi. So, as long as legal fixtures are being used (and flow restrictors are not removed - which should not happen anyway), this should be ok for a shower; however, if the tub is large, the water may be cold by the time the tub is full. Many fixtures, such as waterfalls and raincans may require more water volume to operate properly.

A pressure-balance valve with an integral diverter is designed ONLY for a shower/tub spout combination; don't try using one to divert between a showerhead and a handshower.

Finally, if you want to have more than one fixture producing water in your shower at the same time, this is not the valve for you.

It's important to decide the luxuries you want in your shower before investing in the valves.

Have fun today!

Kaitlyn

Custom Plumbing & Hardware

713-961-1324