FREQUENTLY ASKED QUESTIONS ON THERMOSTATIC MIXING VALVES
WHAT IS A THERMOSTATIC MIXING VALVE (TMV)? – TEMPERING VALVE
TMVs accurately control water temperatures for bathing, showering, hand-washing and bidets. They are designed to maintain the desired water temperature, even when the incoming water pressures/flow rates change.
HOW DOES A TMV WORK?
Function
Hot and cold water entering the valve is mixed to a temperature pre-selected by the user or installer. A thermally sensitive mechanism within the valve automatically proportions the amount of hot and cold water entering to produce the required blend. The mechanism then automatically compensates for any reasonable variations in supply pressures or temperatures within the design range to maintain the pre-selected temperature. In the event of cold water supply failure, the thermostatic mixing mechanism will automatically shut down the flow to prevent discharge of dangerously hot water. The flow will also be shut down in the event of a hot water supply failure to prevent thermal shock. In the event of a sudden supply temperature increase (‘spike’), the TMV will quickly (but not absolutely instantly) adapt and deliver water at a safe temperature.
Main components
Thermostatic element
A temperature sensitive element which expands or contracts depending on the temperature of the water surrounding it. When the thermostatic element senses a temperature change, it moves a piston which changes the proportion of hot and cold water being mixed in the valve. This movement enables the valve to remain stable and to shut down in case of cold or hot water failure.
Piston
Usually connected to the thermostatic element, the piston moves back and forth over the cold and hot ports of the valve, changing the proportion of hot and cold water entering the valve depending on the temperature of the water.
Return spring
When the thermostatic element expands it moves the piston under its own energy and compresses the return spring; when the thermostatic element is cooled, the thermostatic element contracts and the return spring pushes the piston back.
WHY ARE TMVS IMPORTANT FOR SAFETY?
Over three quarters of severe scalds are suffered by children under five years of age, and almost three quarters of the fatalities are people aged 65 and over. By limiting water temperature and stopping sudden increases in water temperature, TMVs help to prevent scalding, which can cause very serious and even fatal injuries. Hot bath water is responsible for the highest number of fatal and severe scald injuries in the home.
Young children and older people are most at risk from bath water scalds because their skin is thinner and therefore less tolerant to higher water temperatures than that of other age groups. As a result, they sustain scalds more quickly, at lower water temperatures and often with a greater depth of burn.
People with a reduced ability to perceive risk or react to hazardous situations – for example those with mental or physical disabilities – are also at greater risk of injury. TMVs help to protect the population from scalding injuries.