This in-wall On/Off Volume Control valve lets you turn the water on and off and control the volume of water. For use with 10 styles of trim kits, including: Berwick®, Copeland™, Green Tea®, Moments™, Portsmouth®, Quentin™, Serin® and Town Square® (all sold separately). Your shower system may also require a mixing valve and diverter.On/off valves operate as their name implies - they turn water on and off and control volume of water. Consider this example of a typical installation - a fixed showerhead with three body/side sprays. You get into the shower with all sprays on to get wet, then (using the on/off valve) shut off the body/side sprays to lather up.