Can anyone tell me what's the difference between a 'Part 1' and a 'Part 2' ball valve? I was trying to get a replacement for a leaking toilet cistern ball valve (very old) that looks like a 'Part 1', but the only ones I can find of this design are for high (mains) pressure. I thought maybe that was what a 'Part 2' is for, but they only seem to be high pressure too. The space in the cistern is very restricted, so alternatives like a Torbeck or Fluidmaster valve won't fit. I'm a bit doubtful even a conventional plastic side-entry valve will fit, as I don't think the float arm is long enough to reach the free space beyond the siphon where the float needs to go. Is it possible to modify a 'Part 1' to make it suitable for low-pressure use?