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Thermostatic
Mixing Valves
Author:
A.Jeffers
Date Written:
22-Oct-07
Copyright © 2006 www.click4bathrooms.com
To begin with, let us look at how a thermostatic mixing valve works. In its simplest form, separate hot and cold water supplies are piped to a heat sensitive control inside the valve. As the mixed water temperature increases, the heat sensitive control expands, closing off the hot supply and opening the cold. When the temperature decreases, the reverse happens in order to keep the mixed water at the desired temperature. This desired temperature is dictated by the client/end-user, but should fall between 37ºC and 46ºC. This prevents scalding. 41ºC is frequently quoted as temperatures of this value and above kill off legionella bacteria, as is 43ºC. This set point/desired temperature is established using a spindle on the valve head, which is then concealed with a cap to prevent meddling.
Whilst this sounds safe and ingenious, a heat sensitive control cannot recognise different water pressures, or the imbalances and pressure fluctuations that often occur in situ. Consequently, the temperature of some older thermostatic valves has been known to fail and cause serious injury.
Leading manufacturers in the UK addressed this problem and developed new thermostatic mixing valve technology. The latest generation of thermostatic mixing valves can cope with different water pressures, pressure imbalances and pressure fluctuations using a single, all-purpose thermostatic cartridge. Some older versions required separate cartridges for high and low pressure conditions. Temperature accuracy and stability has improved dramatically and so has reliability.
Unfortunately, there are manufacturers still using outdated thermostatic mixing valve technology, often in areas with low labour costs. Their products may claim to meet the relevant British Standatd (BS 1415 Part 2), and were available at attractive prices. This may be have been so, but action had to be taken to ensure out-dated and potentially dangerous/unreliable technology was filtered out. The result was TMV3 - Type 3 Thermostatic Mixing Valves – a standard of enhanced thermal performance. If a thermostatic mixing valve carries this kitemark then it will very likely be a much safer and reliable valve than alternativves without this certification.
