hydraulic mule for annuals
 

This questions applies to Skymasters with engine driven hydraulic pumps

I need a hydraulic mule for powering the gear system on my ‘1966 337 during annual maintenance. Does anybody know of a good solution for this? I have seen “homemade” types and I am sure Cessna must offer something (for lots of money) I am just wondering what others are doing to power the hydraulics during annuals


Steve

I went the "homemade" route. It was several years ago but as I recall it required about 3-400 dollars in parts plus a weekend for assembly. It does not need to be terribly sophisticated. The major pieces are a oil reservoir, oil filter, motor and hydraulic pump with coupling, pressure regulator and gage, hoses and couplings along with assorted pipe fittings and valves. The service manual provides a general design concept. The only element that is not obvious is that the mule will provide an unlimited amount of oil up to the reservoir capacity that quickly fills the aircraft system and then is pumped overboard requiring that tubing be run from the aircraft overflow back to the mule reservoir otherwise you can very quickly pump a few quarts of oil on to the shop floor. Also, the hose fittings need to be obtained from Aeroquip or similar because they use a different flair angle than standard hydraulic fittings. I built the whole thing into a metal service cart for mobility. Consider that the aircraft connections are made 6' off the floor when up on jacks so plan hose lengths accordingly.

We mule we built is just a pump, motor, filter, and hoses. just disconnect the lines on the fwd firewall hook the mule lines up, make sure they are full of fluid, plug it in and you're ready to go. I wired a remote switch on mine so I can bump the gear up while I watch. Found a steel ammo box that is @18X30X10 that everything fits in and have even put it on the airlines.
Kim

I made my own as well. My unit is a manual one. I used a large manual hydraulic pump and a large reservoir. The Skymaster system doesn’t use a tremendous amount of flow. Total cost was about $200.00. Initially I built it for testing cracking pressure for rebuilding the hydraulic powor pack in the early Skymasters. Works quite well. I’ve had a few shops borrow it for their annuals.

What kind of pump, electric, did you use Kim.??
I'm looking at building one over the winter, so I have it for the spring annual.

Larry
I think we used a 3 HP motor, which is about as big as you can run on a 20 amp circuit. I can't remember the GPM for the pump but it was larger than we needed and was compatiable with Mil 5606. We bought all the stuff from Northern Hydraulics including the flexiable coupling and the pump mounting adapter. I'll be out of town for the next week, on the road with the fleet, but I'll get some specs. and pictures to you when I get back.
Kim