Intafil Plus 12L Vessel and Kit features an expansion vessel, filling loop, double check valve and isolating ball assembly, ball valve and safety relief valve with gauge. It absorbs an increase in water volume to maintain a constant level of pressure in the central heating system for efficiency. The pressure gauge is used to make a temporary connection between a mains water supply and a sealed heating system. It can be used to manually fill or top up a heating system if the pressure has dropped too low.