John Guest Speedfit Double Check With Service Valve 15mm (Pack of 5)John Guest push fit acetal double check service valve provides protection from the reversal of flow or back siphonage against Fluid Category 4 risks. he low headloss design, is suitable for potable liquids , foodstuffs, intermittent hot water (up to 50oC max and in accordance with The British Beer and Pub Association Code of Practice), water treatment and purification applications. Fast and simple to install, John Guest valves create an instant push