These are water valves that can be set to maintain a constant output temperature when given hot and cold supply lines. How do they know what the temperature of the hot and cold lines are and how much of each to combine to maintain the set temperature without requiring electricity to power sensors and an actuator?
Two more questions: Do they have a risk of failing such that it flips to fully hot and burns the user at the tap, and what happens if you set the output temperature above the temperature of the hot line?
In: Engineering
So the valve is set up with a thermostat and knob controlled piston. The hot and cold water enter the valve and are mixed at a specific ratio determined by the knob. In order to maintain this ratio of hot and cold there is a thermostat similar to the one regulating your car. The thermostat has a little piston on a copper tube filled with paraffin. When the water heats up around the thermostat the paraffin expands and moves. This allows more cold water in. This system self regulates the temperature of the water. As for your other questions there is always the possibility of a valve failing and I suppose there could be a case where you get only hot water but if the piston where to break the natural mixture of hot and cold is at a comfortable position. As for turning the temperature up you can probably guess that you’ll only get hot water and no cold water therefore the hottest it will allow is the hottest your hot water can get.
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