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The recent discussion of leaking Lancair hydraulic
cylinders caused me to reminisce about my time spent in fluid power component
sales and got me to dust off some old cylinder catalogs. Most, if not all,
hydraulic cylinder manufactures of the type we use offer several levels of
quality and at the bottom of the list are the lowest price and lightest duty
ones that utilize o-rings for all the seals. The higher quality versions
use u-cup seals on the pistons and where the rod exits the barrel and usually a
rod wiper to keep wear-inducing particles from getting to the rod seals.
U-cup seals are V shaped with the open side toward the pressure source. A
double acting cylinder, like the ones we use, have two on the piston, one facing
each direction. It doesn't take much imagination to see how this
arrangement will greatly prolong internal leakage across the piston. They
also have a lower breakaway force than an o-ring seal because they are
self-energizing and don't rely on an interference fit to seal. I would
challenge anyone on the list who is adept at web searching to see if cylinders
with the good seals can be found that have the same external dimensions.
Cylinder manufactures commonly do special dimension cylinders at very little
extra cost. What we're asking for are double acting hydraulic cylinders
with u-cup seals (some might have a different term for them) that can be
supplied dimensionally interchangeable to the ones we are using now. You
might also be surprised how relatively inexpensive these will be.
Leighton Mangels
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