With such a huge choice of mixer valves available in the UK, it’s not always easy to know which is best for which job – so what exactly is the difference between a TMV2 (thermostatic mixer valve type 2) and a TMV3? Steve Saunders, Triton’s senior technical manager explains…
Two of a kind
TMV2 approved units conform to BS-EN 1111 (high pressure) and/or 1287 (low pressure) standards and work under pressures of between 0.1 to 1 bar and 1 to 5 bar. The most notable difference between TMV2 and TMV3 is that a TMV2 shower will have been designed, built and tested specifically for the domestic housing market so will provide perfectly adequate temperature control for mainstream use.
Where TMV2 mixers really come into their own is compliance with the UK’s current building regulations. The introduction of Part G of the Building Regulations (hot water supply and systems) in 2010 means that all new homes have to be fitted with a protective device to limit the temperature of hot water from bath taps and shower mixer taps to a compulsory 48˚C in order to offer a safeguard for end users.
One of the simplest ways to ensure compliance with this standard is to fit a TMV2 bath shower mixing valve which will prevent water temperatures from fluctuating if, for example, a tap is turned on or a toilet is flushed. Should there be a loss of flow to either incoming supply, water from the shower will stop or be reduced until both supplies are restored.
TMV3 – a magic number?
Sitting at the opposite end of the spectrum, TMV3 valves are now widely specified in the healthcare sector, which includes establishments requiring a duty of care such as care homes or housing association properties. TMV3 accreditation confirms that the product complies with the higher NHS Estates DO8 specification for thermostatic mixer valves, making it suitable for patients and residents in healthcare premises.
The real strength of TMV3 products is that they are independently tested by the Water Research Centre Limited (WRC) to ensure valves consistently adhere to the stringent requirements of the DO8. Mixers compliant with these specifications gain type 3 certification after testing and are then deemed suitable for use in any application where risks associated with showering must be reduced. In addition, type 3 TMVs must be designated as being suitable for either high or low pressure water systems as well as being compatible with a number of applications including showers, baths, washbasins and bidets.
Accreditation for TMV type 3 showers is administered independently by Buildcert and is granted on a five year period of approval, after which manufacturers must resubmit their product for another TMV3 test approval. The great thing about this is that it keeps the installer protected by ensuring the TMV3 valve always carries the appropriate certification. What installers do need to bear in mind however is that they are responsible for carrying out specific tests six weeks after installation in addition to annual checks to ensure the valve still adheres to TMV type 3 performance.
With such significant differences between the two standards, it is important for installers to be aware of both prior to the selection and installation of a suitable shower. Demand for thermostatic options is only likely to grow, as is the knowledge of the end-user with access to the internet. This is where manufacturer training courses and technical support hotlines can really help the industry’s professionals.
Further information