Combined pressure reducing valve and strainer. The pressure reducing valve limits water pressure to 3.5 bar (50 psi). The strainer filters coarse impurities from the water supply. Connection 1/2" BSP female. Installation Pack U1 must be installed on the cold inlet side of the heater and before the expansion vessel. Where possible, installation should be on the mains side of the cold water tap draw-off. This will result in balanced water supplies and is particularly important when mixers are to be used. Pack U1 must be used with Pack U2.