Dany
The whole thing about Hydraulic conversions is that they are really quite simple to get to work well. You do not need an expensive 'system'. Think of it as a liquid based pneumatic system with a few extra items.
Ok here is a list
You need:-
1) a means of getting pressure i.e. a pump. Standard kero pumps work well except for the very small Flightworks one.
http://www.xicoy.com/catalog/product...roducts_id=237
2) A means of limiting the amount of pressure. An accumulator system as Mick uses made from an old cylinder with a spring fitted on one side that operates a micro switch OR a pressure limit switch like the GEMS PS61-19-4MGZ-B-SP (this is fitted in the negative line of the servo lead to the servo switch. The pressure switch will need tapping M5 and fitted with a Festo M4 fitting
http://uk.rs-online.com/web/p/pressu...tches/7794238/
3) A servo operated switch like the Battleswitch that turns the pump on
http://www.dimensionengineering.com/...ch-diagram.jpg
http://www.lipoly.de/index.php?main_...d=Battleswitch
4) High pressure 4mm od pipe. Use Festo special tube or Nylon that will stand 225 psi is required for all lines.
http://www.kiowa.co.uk/Festo-PAN-R
5) A valve, the Eurokits one is best but the UMS one is also ok. It is available separately. (The valve is operated with a servo the same way as a pneumatic system.)
http://www.airfighter.eu/Fahrwerke/e...aulics/Eurokit
6) An oil reservoir tank, the UMS one is good and has a nice O ring seal.
http://www.hobbyking.com/hobbyking/s...etracts_.html7) The retract cylinders need tapping M5 and fitting with Festo 4mm fittings
http://www.kiowa.co.uk/products/QSML...P00016769/1008
8) The Incoming line to the valve needs a M4 Festo non return or check valve (this is a spring loaded ball inside the fitting)
http://alshobbies.com/shop/cat.php?i...=21&NumShow=20
9) Oil, I used Citroen hydraulic LMM+ fluid.
http://www.ebay.co.uk/itm/like/28101...d=604521252137
10) Battery to power the pump, I used a small 1100 mAh A123 2 cell pack, but a small Lipo would also do.
The connections are simple just as you would of pneumatics except you need the pump, the pressure limiter and the one way valve on the line into the valve. It can be a bit messy when you first put the system together so keep plenty of paper towels handy. Just be aware if you undo a Festo with the system under pressure it will squirt oil out. You will soon get the hang of how to bleed the system and should be very pleased with the results.
If you use an electronic sequencer or a Powerbox Cockpit SRS you should be able to switch the pump as part of the retract cycle rather than leaving it on all the time at the flying field.
Hope this all helps.
John