"Trevor Jones" wrote: A closed system, positive action (to deal with mud,
damage, or decay),
and the ability to have the trailer both move as required, and be locked
in the desired position hydraulicly, are what comes to mind. (clip)
^^^^^^^^^^^^^^^^
My automotive bottle jack, my automotive hydraulic scissor jack and my
hydraulic press are all single acting. They do not present any problems
from the fact that they take in air as the cylinder extends. As to locking
the tilt bed in place, that is accomplished by closing a valve, trapping
fluid in the cylinder. The extra complexity of a double-acting system to
handle the possibility of sticking seems like huge overkill.

You could, of course, slip the end of the trailer under a load, and use it
for lifting, or maybe for pulling stumps.