Shower valves use three different types of mechanisms: pressure-balance valves, thermostatic valves, and single-handle valves. Among these three, single-handle valves are the simplest. Not surprisingly, their features are also limited. Thermostatic valves are very advanced. They can detect the temperature of the water and control the volume of water that comes out of the heads. Thermostatic valves are really useful because you can set the temperature of the water and save yourself from scalding in the shower.