You guys with air operated retract systems on large plane should look at Hydraulic systems. I tried everything on my Arado 555 for retracts and installed huge air piston cylinders, large throughput valves and big tanks. They failed to close the doors in the air. I changed to electric retracts which were in their infancy at the time but again they did not work in the air making landing with partly extended legs interesting.
Retracts are modified Behotec C50 units with Festo fittings and high pressure Nylon lines with the pressure relief valve set at 120 psi. magomhrc.com do a thinner pipe that is held with metal sleeves that will be easier to install.
Boulton Paul system based on Magomhrc.com units
Final version of the system for the Gotha using simplified Magomhrc.com units
Mk 1 system as a trial rig for my Gotha P60 before the Magomhrc units had become know about.
This may be of interest to those that have not seen it before apologies for those that have seen it before
John