The foot controlled units like Enerpac are a piston arrangement that cycles.
When you press on the treadle the air shuttles a pistion back and forth
pumping hydraulic fluid. We have one at work that we use once and awhile
when we have to use the porta-power cyuylinder repeatedly. The air is only
causing a little hydraulic piston to cycle. On ours if you press the other
side of the treadle the cylinder bleeds fluid and retracts.
Randy


"Bob Engelhardt" wrote in message
news
When an hydraulic jack is used in a press, there is very little stored
energy. So if you're pressing something and it's sticking, but suddenly
lets go, nothing happens. But in air over hydraulic, there is a lot of
stored energy. Do you get a "lurch" when something sticks and then lets
go? Or is there something built into the jack to control this? E.g., a
flow-restricting orifice?

Thanks,
Bob