A pressure-balanced valve provides water at nearly constant temperature to a

shower A shower is a place in which a person bathes under a spray of typically warm or hot water. Indoors, there is a drain in the floor. Most showers have temperature, spray pressure and adjustable showerhead nozzle. The simplest showers have a ...

bathtub A bathtub, also known simply as a bath or tub, is a container for holding water in which a person or animal may bathe. Most modern bathtubs are made of thermoformed acrylic, porcelain-enameled steel or cast iron, or fiberglass-reinforced poly ...

, despite pressure fluctuations in either the hot or cold supply lines. If, for example, someone flushes a

toilet A toilet is a piece of sanitary hardware that collects human urine and feces, and sometimes toilet paper, usually for disposal. Flush toilets use water, while dry or non-flush toilets do not. They can be designed for a sitting position popu ...

while the shower is in use, the fixture suddenly draws a significant amount of cold water from the common supply line, causing a

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

drop. In the absence of a compensating mechanism, the relatively higher pressure in the hot water supply line will cause the shower

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

to rise just as suddenly, possibly reaching an uncomfortable or even dangerous level. Conversely, if someone opens a hot water faucet elsewhere, the relatively higher pressure in the cold water supply line will cause the shower temperature to drop suddenly. This is described in US patent 3674048. The pressure-balanced shower valve compensates for changes in water pressure. It has a diaphragm or

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...

inside that reacts to relative changes in either hot or cold water pressure to maintain balanced pressure. As water pressure drops on one supply line, the valve reduces the pressure in the other supply line to match. A side effect of this is that the pressure and flow at the shower head or tub spigot will drop twice as much as if only one supply line had been affected, but without a large temperature change. There are

ball bearing A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this ...

s in the valves to regulate forces. The use of pressure-balanced valves can prevent scalding injuries, in particular to the elderly, the infirm, to children and infants. Based on that, some municipalities require by

building code A building code (also building control or building regulations) is a set of rules that specify the standards for constructed objects such as buildings and non-building structures. Buildings must conform to the code to obtain planning permission ...

s to have it installed.

References

{{reflist Bathing Plumbing Plumbing valves

See also

References