Part 1 and Part 2 Float Valves

[peter anderson]

Does anyone know where part 1 and Part 2 float valves should be used and why?

 

[billy bob]

Part 1 ballvalves should not be used on mains supply, because the outlet can be submerged in an overflow situation which could allow back siphonage
Part 2 ballvalve are sutiable for use on mains because the outlet is at the top an air gap is still maintained in an overflow situation

 

[peter anderson]

So part 1 wouldn't be used in cold water cisterns or feed and expansion cisterns or WC cisterns supplied direct from the mains? Does that mean part 1 are only used in WC cisterns supplied from a tank. Are they used anywhere else? In an overflow situation wouldnt water still go into the inlet even with part 2?