Question: what is the difference between a part 1 and part 2 float valve?
Answer: On a Part 1 or 'Portsmouth' valve, the outlet is on the underside of the valve. On a Part 2 or 'diaphragm' valve, the outlet is on the top of the valve. ... If a Part 1 ball valve fails and the water level in the cistern reaches the pipe centre line, there will be no air gap between the valve and the water in the cistern.