Large Hydraulics


schweiss hydraulic door

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.

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Paul Dye
Paul Dye, KITPLANES® Editor at Large, retired as a Lead Flight Director for NASA’s Human Space Flight program, with 40 years of aerospace experience on everything from Cubs to the Space Shuttle. An avid homebuilder, he began flying and working on airplanes as a teen and has experience with a wide range of construction techniques and materials. He flies an RV-8 and SubSonex jet that he built, an RV-3 that he built with his pilot wife, as well as a Dream Tundra and an electric Xenos motorglider they completed. Currently, they are building an F1 Rocket. A commercially licensed pilot, he has logged over 6000 hours in many different types of aircraft and is an A&P, FAA DAR, EAA Tech Counselor and Flight Advisor; he was formerly a member of the Homebuilder’s Council. He consults and collaborates in aerospace operations and flight-testing projects across the country.


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