CWS float valve: part1/2 compatibility

[phloaw]

Tonight the arm of the ballcock feeding the cold water storage cistern in my attic broke (quite puzzling: maybe due to strong wind causing some turbulence??).
Anyway, I need to replace it. I know it's faster to replace only the part inside the tank, undoing the very last compression nut.

But can I do that when passing from a "part 1" to a "part 2" valve?

Otherwise, I might choose to stick with part 1 to cut the hassle.

PS: I'm talking about an open vented pumped S-plan system, common here in UK, aka "hydronic heating system" in USA.

 

[moonlight]

If you undo the large nut inside the tank the one attached to the valve. See picture below.

You can just swap them over the nut are the same size, you may need to move the float up or down on the arm to get the correct height of water in the tank. You may even have to bend the arm to get the correct height for the water leve.