Ford E-350 with ETI Boom Lift repair

[backyardhandyguy]

Hey everyone. I'm just starting out in the world of hydraulics but I'm no stranger to tearing apart many things mechanical. I'm not sure if this is the correct location for this topic either, but I'm going to give it a shot.

I have a Ford E-350 cargo van with an ETI boom lift on it. I grasp the idea behind hydraulic Pistons common valves, and all that stuff, but I'm not familiar with the actual terms for the parts and the intricate inber workings of the system.

Last night as I was using the lift, a nut on one of the pistons started leaking fluid. It's not spraying, but it is leaving puddles after hours of use. I have included pictures of the nut is question. Somebody who briefly looked at it told me that its purpose is to control the pressure inside the cylinder. I tried researching it and the best I could come up with was "jam nut."

I'm wondering if anyone kreading this knows about these things and can point me in the proper direction. I'm guessing it is just a bad o-ring but before I tear it apart, I had some questions about best practices and what to expect.

Photos here:
http://imgur.com/a/PGpJRnZ

 

[92U 3406]

That looks to be a counterbalance valve. They are a safety feature on aerial work platforms. If you blow a hose it keeps the boom from crashing back to Earth. Basically its just a valve that will open once oil pressure has increased enough to overcome the valve's internal pressure setting, which happens when you force oil into the rod end to retract the cylinder. Force transfers to the base end and the resulting pressure rise in the base end opens the counterbalance valve and lets the cylinder retract.

As for the leak, I've honestly not had much success with putting seal kits in them. I normally just replace the entire counterbalance valve cartridge.