A HYDRAULIC TEST STAND by Don Wall, EAA 218017
5471 Lake Howell Rd., Ste. 202 Winter Park, FL 32792
During the fabrication of the hydraulic hoses for my custom built, I ran into the requirement that these hoses should be pressure checked at 50% greater than expected operational pressure. The output of my aircraft's hydraulic pump was stated to be about 2000 psi. To check the hoses at about 3000 psi for integrity and leakage, I needed to come up with an economical solution. Compressed gas as a pressure source was quickly rejected since high pressure gases are quite explosive if a rupture occurred. High pressure electric hydraulic pumps were considered too expensive. I decided that if I could "capture" a hydraulic ram, such as from a bottle jack, then I could develop plenty of pressure. I purchased a 6 ton hydraulic jack at a local auto parts store for under $10. The diameter of the lift cylinder was measured as 1.22 inches. A quick calculation revealed that this jack could develop over 10,000 psi. The lifting capacity is simply the product of the internal pressure times the area of the lift cylinder. Most inexpensive bottle jacks have a bypass at the top of the extension of the lift cylinder. Hence, the jack needed to be "captured". To gain access to the pressurized fluid, I drilled and tapped a 1/8 NPT port in the bottom of the jack. The jack was about 3/8 inch thick in this area. I tried to center the hole directly below the lift cylinder. A small piece of 2 inch steel channel was bored/cut to accommodate the two threaded drill rods and also let the copper tubing connect to the bottom of the jack. One quarter inch flared tubing was used to connect the NPT port to the pressure gage tee. A O to 5000 psi gage was found in 58 APRIL 1990
surplus and connected to the tee. Most welding gas supply stores carry inexpensive gages that go up to 4000 psi. A flex hose then came off the tee which is used to connect to the test specimen. Most bottle jacks have a reservoir port located along the outside about halfway up. Note: you will need to drain this fluid, prior to drill/tapping the hole. After tapping, flush out all the metallic particles. After connecting the tubing, you will need to fill the reservoir with a suitable fluid. Water can be used, however, I would not recommend it since it is very corrosive. I used automobile transmission fluid, Dexron II, in my test apparatus. To capture the ram, 5/8 inch threaded steel rod was used with a small plate to hold the top of the lift cylinder. The above photo is a view of the test apparatus. The test stand was fabricated from 1/2 inch plywood and 2x4s. A small vise works great as a holding fixture. This test apparatus has been oper-
ated at pressures around 3000 psia. Since it contains liquid, a sudden break or rupture in the lines simply lowers the pressure without any explosion such as may happen with a gas medium. Of course, a little fluid pops out. Prior to pressurizing, any air should be bled from the system just for this reason.
Readers are invited to submit entries to EAA,
Hints For Homebuilders, Att: Golda Cox, EAA Aviation Center, Oshkosh, Wl 549033086. Entries will be reviewed by a "panel of EAA judges. Readers whose hints are published in any EAA magazine will be awarded one of three monthly prizes - a 3/8" Drive Socket Wrench Set, a 1 /4" Drive Socket Wrench Set or a Nine-piece Long-Handle Combination Wrench Set. The contest will
run from August through July of each year with a Grand Prize of a Snap-on Tools KR657 Roll Cab and KR637 Top Chest being awarded the best entry for the year. This award will be presented during the EAA Convention beginning in 1989. Our thanks go to Snap-on Tools for providing the awards.
