The above animation shows how a Horne thermostatic mixing valve or TMV works to proportion the mix of hot and cold water to provide blended water at a set temperature. The expansion and contraction of the internal thermostatic element moves a slide valve - altering the aperture of the hot and cold inlet ports to the inner mixing chamber thus constantly adjusting the blend of hot and cold water.
Thermostatic performance of the TMV can be verified by conducting a Cold Water Failure Test as shown in the animation: gradual failure of the cold water supply causes the thermostatic element to expand fully as it becomes increasingly bathed in hot water. This expansion moves the slide valve to the fully closed position over the hot port and thus flow at the outlet ceases. If the flow does not reduce to a dribble, then maintenance may be required to restore the valve to optimal performance.
