A Croydon ball valve is a ball valve which consists of a piston inside a brass housing, with a float arm secured to the valve via a brass split pin. On the end of the float arm is a plastic or copper float.
Inside the valve, the piston carriers a washer, which faces the valve seating. When the water level in a cistern falls, such as in a cold water storage cistern or feed and expansion cistern, the piston is moved away from the valve seating, opening the valve and allowing water to flow into the cistern. As the water level in the cistern rises, the upward force of the float pushes the piston and its washer back onto the valve seating, closing the valve.
A Croydon ball valve operate in exactly the same way as Part 1 ‘Portsmouth’ pattern ball valve, except that the piston which carries the washer moves vertically instead of horizontally.
Both Croydon ball valves and Part 1 ball valves are being phased out in favour of Part 2 ‘diaphragm’ ball valves. This is because they do not offer an effective air gap between the water outlet on the valve and the pipe centre line, increasing the risk of back-siphoning into the mains in the event that the valve should fail. Another reason why they are being phased out is because, unlike Part 2 ball valves, they are not equipped with a mechanism to adjust the water level in the cistern – the only way to do so is to physically bend the float arm.
A Croyon ball valve may also be equipped with a ‘silencer’ tube – an extension of pipe which dips down into the water in order to reduce the noise of the cistern filling. Current water byelaws prohibit the use of such fixtures on cisterns.
For the above reasons, Croydon ball valves are no longer permitted on cold water storage cisterns, and should be replaced with a Part 2 ball valve.