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TECHNICAL
Thermostatic Mixing Valve
By Patrick Gordon of Calafrica ( technical @ calafrica . co . za )
Patrick continues his series on valves and how they operate .
Q – How does a Thermostatic Mixing Valve work ?
Most domestic hot water systems support temperatures of more than 60 ° C . This temperature is maintained to make the system safe from bacteria like Legionella . This temperature however exposes the user to the risk of scalding . Under normal conditions this is not a problem as the average person ’ s reaction speed is such that they can remove themselves from the exposure before suffering serious injury . However young children , old people and disabled people have slower reactions and are thus at risk . The set temperature of the system cannot be reduced without the risk of bacterial infection . The only way to make the system safe is to regulate the terminal temperatures by using a thermostatic mixer with an anti-scald feature .
The regulating element in the thermostatic mixing valve consists of a temperature sensor that is fully immersed in the mixed water outlet pipe which , by expanding and contracting , continuously ensures the correct proportioning of hot and cold water at the outlet . The water proportions are regulated by a piston that slides inside a special cylinder that is placed between the hot and cold-water passage channels .
Even if the pressure drops due to hot or cold water drawn-off by other users or temperature variations at the inlet , the mixing valve automatically adjusts the water flow rate until the set temperature is achieved . A mixing valve with an Anti-scald feature will totally prevent hot-water flow if the cold-water flow should be interrupted . This may inconvenience the user , but it will safeguard them against serious injury .
After you have adjusted the valve to the desired temperature , you can lock the setting by using the control knob . To achieve this , unscrew the retaining screw at the top of the control knob . Remove the knob and then replace it so that the spline on the inside of the handle matches with the spline on the adjustment mechanism .
But how does it do this :
To protect our valuable friends and family , get a qualified plumber to fit a Thermostatic Mixing Valve to your system .
All images supplied by Patrick Gordon
For any further information regarding this topic please feel free to contact Patrick Gordon on : + 27 ( 0 ) 83 303 1437 . PA
“.. but it will safeguard them against serious injury .”
www . plumbingafrica . co . za @ plumbingonline @ plumbingonline @ PlumbingAfricaOnline July 2023 Volume 29 I Number 5