Rob thanks for the kind remarks. I would recommend using hydraulic if they are large wheels with doors that have a big drag from the air stream. The only downside is the mess when playing with them!
I have now had a chance to test the UMS system.
My findings are
1) the top up tank is nice small and light with good seal and good fittings.
2) the electronics I do not like. The system on smallest setting does not seem to switch off so must be very high pressure.
3) the valve is fine, but had barb connectors as opposed to the Eurokit one which has nice push fit connectors, the valve did not leak.
4) The motor as some report gets hot quickly and in comparison with the very small Xicoy unit does not push the oil as efficiently
I am grateful to David Gladwin for sending it to test.
I have also tested the GEMS pressure switch and that works fine except it has a very small deadband and the slightest fall in pressure kicks the pump back into life. It tends to sit there twitching every few seconds. That would not be a problem if the pump actuates as part of the sequence for landing gear. I am inclined to use the switch in the plane as it is a little neater and easier to install than the cylinder. I did wonder about using a tank pressure switch that has a bigger deadband but not sure if it would stand up to the hydraulic fluid.
I tried the UMS pump with the pressure switch and it dies not seem to switch off easily as it leaks past the gears so much and twitches for longer than with the Xicoy one.
John