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Old November 25th 20, 11:01 PM posted to rec.aviation.soaring
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Default COBRA Hydraulic Jack

On Wednesday, November 25, 2020 at 12:32:05 PM UTC-5, BG wrote:
For those considering replacing their leaky Cobra hydraulic jack, better to replace the seal than deal with the cheap replacement that does not really fit. At least that is what I found with the Harbor Freight solution. I think it does not have the same stroke as I recall. I replaced mine about 8 years ago on now a 20 year old bottle and still working fine today.

Cost $5.42

http://www.mcmaster.com/#mechanical-seals/=ekh96p

part number 9505K82

Buzz Graves


That's a good choice, Buzz! The key with all Polyurethane seals is to keep the fluid as dry as possible, meaning to keep the water content as low as possible. Polyurethane suffers from hydrolyses, the process by which water slowly penetrates and then dissolves the material from the inside out. The higher the pressure and the higher the water contents the faster the process progresses. Pressure is low in this application but the amount of water that accumulates in fluid may be high, so draining and replacing the oil in the jack may not be a bad idea to keep the seal happy.

Uli
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