Apr 102012

Shower valves and shower faucets are dependent upon each other to function. Whereas the faucet mostly refers to the part that you see, the valve is the piece just behind the faucet that makes the shower work.

When turning on the water for your shower, you want to balance the hot water with the cold water. Yet, they don’t flow through at the same rate. You will want more of one than the other. It is the valve that allows both hot and cold to flow through the faucet, as well as regulate how much of each type you want. Without a shower valve, you wouldn’t be able to control the temperature of your shower.

Types of Valves

There are two main types of shower valves:

  1. Pressure Balance Valve
  2. Thermostatic Valve

Pressure Balance Valve

Grohe 35015000 Grohsafe Universal Pressure Balance Rough-In Valve, Chrome
Generally, a pressure balancing valve is found on the types of shower faucet that has a single knob that controls the temperature depending on which way you turn the dial.

A pressure balance valve keeps the water at an even temperature, despite pressure changes in the supply lines. That’s a fancy way of saying that the temperature remains the same even if someone flushes the toilet, or runs hot water in the kitchen sink while you are in the shower.

When the toilet is flushed, it refills with cold water. That pulls cold water away from the shower, which can lead to the water getting hotter quickly. While this may still happen, the valve will prevent the water from getting scalding hot just because the cold is being pulled elsewhere in the plumbing.

In the same way, if someone is running hot water to rinse dishes in the kitchen sink, they are pulling hot water away from the shower. This could cause the shower water to suddenly turn freezing, making you shiver unexpectedly. However, the valve prevents this from happening, again, balancing the pressure coming through the plumbing feeding the shower, compensating for the pressure changes as the hot water is being pulled elsewhere in the home.

The valve balances this pressure by dropping the pressure in the other supply line. In some instances, this will result in a noticeable drop in water pressure in the shower, but you won’t have the drastic temperature changes. In the end, it’s better to drop water pressure, than to have the temperature change suddenly and possibly cause burning.

Pressure balancing valves are definitely important in preventing scalding or sudden cold water changes. However, they aren’t as precise as they could be. There are times when the pressure, and temperature, changes too rapidly for the valve to keep up. This can easily lead to scalding or falling as you jump out from under the suddenly hot or cold water.

Thermostatic Valve

Honeywell R-AM-101C-US-1 Thermostatic Mixing Valve
On the other hand, a thermostatic valve works differently, and can do a much better job at regulating the temperature in your shower.

The water temperature can vary at different faucets in the home, even if you turn the hot or the cold water on completely. Distance to the hot water heater, or from the cold water supply causes this.

A thermostatic valve, also called a thermostatic mixing valve, works by adjusting the temperature of the water at the faucet, based on temperature, not pressure.

There is a thermostat in the valve itself that senses the temperature of the water. This is based on paraffin, or wax, that expands and contracts as the temperature changes. As the temperature changes, the valve automatically adjusts the amount of hot and cold water entering the valve. It then allows the water to flow out of the faucet, assuring that the water is the right temperature before it even exits the valve. The wax mechanism allows for either the hot or cold supplies to be opened wider or closed, or a combination, to maintain a steady temperature.

A thermostatic valve also has a built in fail safe setting that will prevent the water from going to one extreme or another in the case of one supply being shut off. These valves have a mechanical adjustment that allows for the precise setting of temperature, within the range the valve allows.

This type of valve is of course more expensive, which is why they are often seen in high end, luxury, bathrooms. A thermostatic valve is needed for the programmable showers that set the temperature to a specific temperature at the touch of a button.

Another advantage of a thermostatic mixing valve relates to bacteria in the water supply. In my city, as I’m sure in other cities, a plumber cannot set a hot water heater to a temperature above 120 degrees F. This is because above this temperature, it is very easy to get burned.

However, hot water heaters do have higher settings, which are appropriate for sanitation uses. For instance, in commercial kitchens, the dishwashers are set much higher to intensely clean and sanitize dishes.

With a thermostatic mixing valves, you can have it both ways in your own home. You can set your hot water heater to a higher temperature, therefore killing any bacteria in the water. Then, at the faucet itself, the thermostatic valve will lower the temperature of the water, preventing the water that actually reaches your skin from exceeding 120 degrees. The best of both worlds.

The valve behind your shower faucet is important in regulating the temperature of the water coming from that faucet. From the user perspective, you turn the handle. But, behind the scenes, there are two types of shower valves doing an important job making sure that you don’t get burned, or frozen out during your shower.

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