The proliferation of plumbing codes across the country requiring protection from scalding tap water has led to the widespread use of mixing valves in both commercial and residential settings.

Mixing valves serve the function of police officers in the hot water system, tempering the often scalding water in the boiler or water heater to a non-harmful, comfortable stream at the faucet.

While the technology in mixing valves isn't new, the penetration of their use and continued market growth has provided consumers with scalding water protection while still guarding against bacteria.

Paul Grant, engineering manager for Leonard Valve Company in Cranston, R.I., said the majority of mixing valves on the market today have bi-metal thermostats that control the temperature of the water flowing through the valve.

"Usually these are two strips of metal that are mechanically combined into a single strip," he said. "One piece has a high expansion rate and the other a low expansion rate, which creates a mechanical movement. We use that movement to change the porting in the valve to control the water temperature."

Sean Perry, product manager for Wilkins, a division of Zurn Plumbing Products Group in Paso Robles, Calif., pointed out that, traditionally, the American market has favored the use of pressure balance valves, probably due to speed of response and lower price. European markets tended to use thermostatic type valves to meet water temperature safety standards.

Today, though, there is wide use of both types of valves in the United States.

Pressure balance valves are commonly found in residential settings in showers and bathtubs, where they maintain a proportional volume of hot and cold water. By balancing the amount of pressure in the hot and cold water lines, these valves maintain the water in a preselected temperature range.

Thermostatic mixing valves maintain water temperature control in a different fashion. When hot and cold water enter the valve's mixing chamber, a thermostat senses the outlet water temperature and adjusts the amounts of incoming hot and cold water to a specific constant temperature. The desired outlet temperature can be adjusted by mechanical means.

In addition to the temperature control function, thermostatic mixing valves incorporate a safety function that shuts off all water flow in the event that the cold water supply is turned off.

Thermostatic mixing valves are used in many commercial and industrial situations, including public and private nursing homes, hospitals, hotels and motels, schools and other educational facilities, aged care facilities, homes for the disabled and detention centers.

Bruce Fathers, director of marketing for Powers, a division of Watts Water Technologies Inc. of North Andover, Mass., said water tempering valves are available for a multitude of applications, in different sizes and flow capacities.

"There are large master mixing valves and manifold systems, often called distribution or source valves, that deliver a large quantity of water throughout a building," he said. "These valves will take 150- to 180 degree Fahrenheit boiler water, mix it with cold water, and temper the resulting mix to 130 F. Then the tempered water is distributed throughout the building."

Other water tempering valves are point of use valves, Fathers noted.

"These are the kinds of mixing valves you'll find controlling showers and basin faucets so the user is less likely to be scalded by hot water," he said.

Fathers maintained that Powers invented the pressure valve in 1924 when it introduced the Style A Mixer, and pioneered the use of thermostatic products. In recent years, the firm melded the two technologies together into a combination thermostatic and pressure mixing valve.

"We're converting all our thermostatic valves to what we call TP technology," he said. "We use a paraffin-based sensor that senses water temperature and adjusts inside the valve for fluctuations in temperature and pressure, assuring delivery of a consistent 100 F flow of water, plus or minus three degrees."

Historically, pressure balancing valves are the most common types made in the U.S., this choice being driven primarily by costs. There are exceptions, but generally a pressure valve runs in the $100 range; a thermostatic mixing valve in the $400 to $500 range; and a combination valve in the $600 range, Fathers said.

The casual observer might think there's a simpler answer to the problem of scalding hot water-turning down the temperature of the water heater. In the past, reducing water heater temperature to 120 F has been recommended to prevent scalding injuries, but reducing the stored water temperature to that level can cause the proliferation of bacteria.

Legionnaires' disease is a type of pneumonia caused by Legionella pneumophila, commonly found in rivers, lakes and other bodies of water. In its natural state, the bacteria is relatively harmless, but when introduced into a plumbing system it can rapidly reproduce.

Studies have found that water temperatures between 68-and 122 F provides ideal conditions and the presence of algae and biofilm supply nutrients for growth of the bacteria.

At water temperatures between 122- and 140 F, the Legionella bacteria can survive, but not multiply. However, at 140 F water temperature, the bacteria die within 32 minutes, according to Mathew R. Freije, author of "Legionellae Control in Health Care Facilities: A Guide for Minimizing Risk."

Thus, by keeping water heater temperatures at 140 F, the incidence of Legionella contamination can be prevented. But that means another method of tempering the water to prevent scalding is needed. And so we have mixing valves.

Kevin Nelson, director of facilities for St. Joseph's Hospital in Tucson, Ariz., said many institutions like his prefer to standardize their mixing valves to allow for easier maintenance and repair.

"We have approximately 180 patient rooms and each one of them has a shower and a sink in it," Nelson said. "Each of those fixtures has an individual point of use mixing valve that regulates the hot water flow."

Nelson pointed out some mixing valves are superior to others in terms of technology, while others may be easier and more economical to rebuild when necessary.

"From a maintenance point of view, we want to see an inexpensive replacement kit that is easy to install," Nelson said. "We've found that mixing valves seem to be lasting around five to six years before we have to rebuild them."

He added that his staff will rebuild a valve a maximum of three times before replacing it.

While there are advantages to having a single valve to maintain, as well as the obvious scalding prevention, Nelson noted there also are disadvantages with mixing valves.

"We have a hot water loop that's always flowing so we have instant hot water," he said. "Usually when a mixing valve leaks it goes from the hot to the cold side because of the higher hot water pressure. We put a half dozen showers on a loop, so when a leak develops, we have to examine each valve and touch the cold side of each one until we find a cold side that's hot. That's our leaking valve."

At the Los Angeles Unified School District, John Fernandez, the plumbing technical supervisor, said the district uses central tempering valves to supply hot water to a battery of sinks and showers.

"We have more than 900 schools that use water tempering valves, supplied by four different manufacturers," Fernandez pointed out. "Our specs call for a valve that will last-our criteria says a hundred years, like institutional faucets and valves. The quality of the product is the chief element we look for."

Fernandez said he has been with the district for 25 years and mixing valves were in use in the schools when he first started work there.

Dan Crawford, a plumbing supervisor with the LAUSD, said there are features on the mixing valves that plumbers like to see.

"As a maintenance feature, we like to see a cold water bypass on a thermostatic mixing valve, Crawford said. "If you don't have hot water, you can still operate the fixture with cold water. Also, it's easier to maintain the system."

Most plumbers find mixing valves to be relatively straightforward to install, according to Kirby Childress, head estimator for Pioneer Plumbing in Tucson, Ariz.

"They are pretty easy to put into a water system, especially in new residential construction," Childress said. "We also are doing some business in changing out older mixing valves for newer ones and we have installed numerous point of use mixing valves in existing systems."

Childress noted that some of the mixing valves can be tricky to work on, but believes that maintenance of the units is the most important element to be considered.

"The strainers get gummed up occasionally, and you have to regularly maintain these valves," he said.

Dominic Solis, director of marketing for Symonns in Braintree, Mass., has found there is tremendous growth in the use of mixing valves across the country.

"Most of the building and plumbing codes are catching up to the fact that the regulation of hot water should be controlled both in temperature and in how it is distributed through the system," he said.

But depending on the type of building, you may see as many as three different temperatures to consider in a system, Solis noted. For instance, a thermostatic valve may loop water at a consistent 120 F throughout a building. Then for a shower, a pressure valve may knock that temperature down to 110 F. For lavatories, it may be reduced to 100 F by a point of use mixing valve.

Solis foresees more growth in the industry, too.

"Currently there are four standards dealing with mixing valves-ASSE 1016, 1017, 1069 and 1070," he said. "And ASSE 1071 is due out soon. We foresee more growth, and more standards and codes written around them."

Doug DeViney, national sales manager for the commercial products division of Conbraco Industries Inc. in Matthews, N.C., noted the industry is beginning to make inroads into the residential use of mixing valves.

He added while most of the installation volume is in higher end homes, more people are beginning to recognize the valuable protection mixing valves provide.

Another market that has some mixing valve manufacturers excited is that which demands emergency tempering valves. These are places like fire stations, ambulance stations, laboratories, and commercial facilities that handle chemicals.

"The emergency safety market for eyewash stations and drench showers is our fastest growing market line in terms of sheer dollars," Fathers said. "A lot of codes now require sending tempered water to these stations instead of only cold water."

Grant agreed: "That market is getting more active," he said. "Emergency services locations and any place that might have a process that could put a chemical on a worker should have an eyewash and drench station."

He added Leonard has sold valves for drench showers to decontaminate patients before entry to a hospital.

"You want the water temperature to be a bit warmer to allow the person to be more comfortable," he said. "And that's where the thermostatic mixing valve does the job."

"This article was originally posted on ww.reevesjournal.com."