Oh heck--no, it's not an airplane part, and I wasn't cruising along at altitude, trying to stay awake - but it is definitely aviation related, since its part of our new workshop, so let's talk about large hydraulics that require gallons of fluid - and bleeding is a matter of pumping enough fluid to empty a four gallon reservoir. Along with working on airplanes, we've been slowly building a shop addition to our hangar, and part of that addition includes a hangar door big enough to roll airplanes in and out for work. Design restriction meant we needed to keep the building low, so the outside wall could only fit a nine-foot high door.
Using a bifold in that opening would have left us without much vertical clearance, so we went with a single-swing hydraulic from Schweiss, and the door and power-pack have been sitting here, waiting for installation and checkout now since last summer. Well this weekend we finally got to power the system up - and I'm impressed. The kit is wonderfully well thought out - all of the hydraulic lines are color coded, along with the fittings, so it would be awfully hard to put it together wrong, even without the excellent step-by-step, pictorial instructions. Charging the system is a matter of disconnecting the hoses from the two hydraulic cylinders and connecting them together - with a pair of male/male connectors supplied in the kit for the purpose - then running the pump for five minutes to fill all of the tubing. The pump module came pre-filled with fluid, and this step took about half that.
We then continued in the manual, re-connected the "up" line to the cylinders, pressed the button, and amazingly, the door opened up for the first time - with no leaks! The clear plastic bottle safety-wired to the cylinder is there to catch fluid coming out of the return line, and we only saw a couple of drops - very clean. It was then a matter of reconnecting all the lines, lowering the door, topping up the fluids--and we have a working door.
Hydraulics really are easy - no matter their size - if you pay attention to the connections, spin all fittings so they aren't cross-threaded before tightening them down, and get all the air out. Whether they are simple aircraft brakes, more complex aircraft systems--like landing gear--or big cylinders to lift a one-ton door, hydraulics are your friend. Lots of oomph for little complexity. And no leaks--that's priceless.