This is not a vintage machine so should be in one of the other forums.
It is very similar to the Simpson Enviro 130 from a few years ago, I had one which I repaired and gave away. There are 5 water levels for rinses, interestingly they are not pressure switch controlled, they are just timed. So the machine fills to the low level which is sensed with the pressure switch, then it adds a little extra water, the time it adds for depends on what number it is set to - on 1 it adds no extra, on 5 it tops up several times. The amount of extra water added with each addition varies depending on water pressure as it is only timed. At my house which has low pressure gravity supply, even on 5 it only added a little extra water. When I gave it away, its new home had mains pressure water, and on 5 it filled above the axle level - drum more than half full of water!
Chris.