AVG MAXISTOP Valve 15mm 1/2" MST-1 is a revolutionary new approach to point of use isolation valves incorporating an adjustable pressure limiting function. When it comes to protecting flexible hoses, mixer tap cartridges, fridges and appliances etc from excess pressure the MAXISTOP MST valve is the perfect choice. One of the reasons for the development of the MAXISTOP was to prevent excess pressure build-up within the flexible connectors and mixer tap cartridges within a building. Although it’s a requirement to fit a 500kPa boundary reduction valve to the property this will only control the pressure within the cold water service and up to the non return isolation valve to a storage water heater. During the heat up cycle of a storage water heater the water within the cylinder will expand and increase the pressure to whatever the pressure and temperature relief valve (PTR) is set to, in most cases this is 1400kPa. This high pressure will remain within the hot water plumbing system until a tap is opened, this can be up to 23 hours per day. It’s important to note that the maximum allowable pressure for many mixer cartridges is 500kPa, cross flow issues may occur when subjected to excess pressure and this crossover could result in a rise in pressure within the cold water plumbing pipe work also.