Thermostatic valves have two handles: one controlling the volume and the other one for the water temperature. This is because thermostatic valves react to the temperature, not the pressure of the water. With the Thermostatic Shower you can change the flow volume without affecting the temperature, which makes water conservation easy: just turn down the flow while shampooing or shaving! This is all possible due to a wax element inside the valve that expands or contracts in reaction to heat. When water exceeds the maximum set temperature, the element expands to reduce the flow of hot water, and allow more cold into the mix. Should either hot or cold supply fail, the valve will close off flow from the other side. The advantage with thermostatic valves is the direct control over output temperature; while your water heater can be set to 120° F, the water coming out of your shower will range between 70° and 115° F (Pre-set temperature is set on the valve to 105° F).