Guide for pressure-balanced and thermostatic shower fittings

 

Two types of valves

Although they are often confused, there are actually two types of shower valves that can be used to balance water temperature and prevent burns.

Pressure-balancing shower valve: With this type, the volume ratio of hot and cold water is measured and adjusted to continuously deliver water at your chosen temperature. When you turn on the water with a single handle, you control the quantity and the temperature at the same time. As you turn the knob, the amount of water increases while you simultaneously increase the temperature.

Thermostatic shower valve: With this option, the actual temperature of the incoming water is measured and the hot and cold water flow is adjusted to ensure an even temperature. With these shower valves, you usually set the water temperature and the water flow with individual regulators: These valves have two regulators, one for the temperature and one for the quantity. The water temperature remains the same regardless of whether the water trickles or flows at full strength. This type regulates the temperature with an accuracy of one degree compared to the setting you make with the temperature controller. The selected temperature is maintained even after the water is turned off, so the next shower is automatically set exactly as you left it. Thermostatic shower valves are considered to be much better than pressure equalisation valves, but they are also much more expensive.

How a pressure compensating valve works

The way a pressure equalising valve works is that it maintains a balanced flow of water between the hot and cold sides. They do not measure the temperature of the water. The valve has either a balancing piston or diaphragm inside the valve body that responds to a drop in pressure in an incoming water supply (either hot or cold) and adjusts the outflow of the opposite water supply accordingly. This ensures that the water does not suddenly become colder or hotter as it exits the showerhead outlet. Sudden changes in water pressure in the supply line may reduce the water outflow from the shower head, but this will not change the temperature.

How a thermostatic shower valve works

Thermostatic shower valves use a sophisticated mechanism that measures the temperature of the water, rather than just reacting to the flow rate between hot and cold water. A wax element inside the shower valve expands or contracts in response to heat, changing the amount of water that flows in from each inlet. This sounds almost exactly like the cheaper pressure equalisation valve, but it has decisive advantages:

The temperature remains the same regardless of the volume set. This makes it easier to use water sparingly.

You can set the water heater to a high temperature, but the shower valve itself can be limited so that the water temperature never reaches a scalding level. So washing machines, dishwashers, etc. can use much hotter water than you want in a shower or bath.

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