[Archived]

Thanks Jon! I wasn’t aware of the reference to pressure balancing used by common shower temperature regulators, that aren’t really temperature regulators. Even the commercial Moen shower system I put in doesn’t have a thermostatic mixing valve.

Watts, and I’m sure others, make thermostatic mixing valves that shut down their output if the set output temperature can not be achieved. From Watts’ web site:

” Many shower and combination tub/shower mixing valves in todays homes use a pressure balanced design. Unfortunately, pressure balanced type valves do not automatically control outlet temperatures, nor do they automatically limit outlet temperatures should the supply temperatures dramatically increase or decrease. Such limitations are potentially dangerous. Further, to prevent users from adjusting the valve beyond a safe operating temperature, pressure balanced valves require setting of the limit stop by the installer. In addition, to accommodate future changes in the hot or cold water temperature, the limit stop would need to be re-set. By contrast, Watts Thermostatic Mixing Valves offer precise control of the outlet temperatures, no matter how the supply temperatures or pressures vary over time.”

Hiding these behind the shower wall really is unnecessary. If someone doesn’t have one installed, do yourself a favor and install one on the output of the hot water. heater.

[Archived]

These types of valves have been around for a very long time and the combination of temperature control plus the safety of a response to pressure variations makes them ideal for our application. In coaches with relatively small pumps for example someone flushing the toilet can cause a pressure drop on the cold side and a pressure balancing feature is going to respond much faster than sensing a change in temperature.

It has been too long since I was involved with the design of medical equipment, but I think the magic number at the time was 115 degrees F. The valves we used would literally shut down if the water temp hit that number because above that temperature the risk of scalding was substantial. That’s how I first made use of the valve.

[Dale]

It looks like pressure balancing may have multiple definitions.

A typical shower control valve is a pressure balancing valve. These limit the mix of hot and cold water such that when the shower control is set to full hot there is always a mix with some cold water, if set to do so. This mixing or pressure balancing valve does not measure water temperature or water pressure.

A balancing valve that regulates hot water output based on both the pressure of the cold water and the output water temperature of the valve is typically referred to as thermostatic mixing valve. Thermostatic mixing valves were rarities, I think, in residential applications in times based, but appear to be more commonplace now. This is driven by the desire to get hot water to no less than 131 degrees to eliminate bad stuff growing in the hot water tank.

FWIW, this is on my to-do list. I put one on my last coach to protect my grandsons.