Wondering about air-over-hydralic jack
 

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

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
...
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

Bob Engelhardt wrote:

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

The "stored energy" should never exceed one pump stroke worth of ram
travel, probably about 1/8" max. The air cylinder is just operating a
second small hydraulic piston pump, one pump stroke per air cylinder
stroke.

Pete C.

Bob Engelhardt wrote:

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

Bob, you're confused about AOH jacks. The air motor just pumps for you, they act
exactly like a hand pump hydraulic jack, only faster. I have a 20 ton press with
a 20 ton AOH bottle jack on it, $79.95 at Harbor Freight a few weeks ago. It is
just what you want -- use the air to quickly get the jack down where you want,
then use the handle to "feel" the press. Sometimes, of course, you want to just
mash it as fast and hard as you can, then the air feature is really boss. - GWE

Grant Erwin wrote:
Bob, you're confused about AOH jacks. ...

Yes, clearly I am, or was. The question should have been "How do AOH
jacks work?". Now I know. Thanks to all - Bob