Gary
So long as the pipe is sealed at one end by the valve the liquid will not run out even without valves. Yes there may be a little air enter the system but cycling the retracts a few times will usually clear them. Yes I ran the ESC at full power on a low power battery pack. You can use a 3 position switch with full power for arming and mid for lower power and off to switch off. Alternatively you can make the channel variable. The choice is yours. I just kept things simple.
I purged the most of the air by disconnecting the Festos at the retracts one at a time so then air is expelled as the cylinder moves towards the fitting and expels the contents of the cylinder. Connecting the pipe that is full of fluid is then clear of air. You do not have to be obsessive about clearing then bubbles but it will work better with none as liquid is incompressible. The filler tank is very small and will need refilling during the bleed process. Bleeding the lines to the retracts is easy.
The system is not difficult or expensive to replicate, why not have a go making up a system on the bench to try it. Very few people seem willing to try anything different and soldier on with air systems when then combination of retract size speed of aircraft and doors attached make it very difficult to work. Do let us all know how you get on.
John
John