I have been looking at pneumatic swing clamps for a particular job.
And even used ones in the size range I need for proper clamping
pressure and really spendy.
So I thought maybe hydraulic swing clamps would work. Besides being
much less expensive the clamping pressures are much higher. The high
pressure could be a problem.
Looking at air over hydraulic pumps makes it obvious that this
could be the much less expensive and more compact route. But I have
questions.
All the pumps I have been looking at are for single acting
cylinders. Can the output from one of these types of pumps be run
into another valve so that double acting cylinders can be used? Like
the way the valving works on my backhoe for example?
And how is the pressure varied? By how far the valve on the pump is
opened? Years ago I operated an Enerpac double acting air over pump on
a hydraulic press. The pump had a direction lever and a pressure
lever. The pressure lever could be pressed very lightly so that only a
small amount of pressure made it to the ram cylinder.
But all the pumps I am looking at just deliver pressure and then
release it back into the tank. I assume but don't know that the valve
must have a pressure holding position.
A friend just reminded me that I already have an air over hydraulic
pump. The 4th (rotary) axis in the Fadal mill connects to this pump
for clamping, so that the table doesn't rotate from cutting pressure.
I'll need to see what the capacity, fluid wise, is and how much
pressure it can deliver. and whether it is adjustable.
If the thing will deliver enough fluid fast enough at high enough
pressure then I can use it. But what if the pressure is too high and
the unit doesn't have an adjustment? I should just be able to add my
own pressure regulator, right?
Thanks,
Eric

On 2018-02-26, wrote:
I have been looking at pneumatic swing clamps for a particular job.
And even used ones in the size range I need for proper clamping
pressure and really spendy.
So I thought maybe hydraulic swing clamps would work. Besides being
much less expensive the clamping pressures are much higher. The high
pressure could be a problem.
Looking at air over hydraulic pumps makes it obvious that this
could be the much less expensive and more compact route. But I have
questions.
All the pumps I have been looking at are for single acting
cylinders. Can the output from one of these types of pumps be run
into another valve so that double acting cylinders can be used? Like
the way the valving works on my backhoe for example?

Yes, of course, there are high pressure four way valves. I once sold a
10,000 psi pump with such a valve. Not that uncommon.

i

And how is the pressure varied? By how far the valve on the pump is
opened? Years ago I operated an Enerpac double acting air over pump on
a hydraulic press. The pump had a direction lever and a pressure
lever. The pressure lever could be pressed very lightly so that only a
small amount of pressure made it to the ram cylinder.
But all the pumps I am looking at just deliver pressure and then
release it back into the tank. I assume but don't know that the valve
must have a pressure holding position.
A friend just reminded me that I already have an air over hydraulic
pump. The 4th (rotary) axis in the Fadal mill connects to this pump
for clamping, so that the table doesn't rotate from cutting pressure.
I'll need to see what the capacity, fluid wise, is and how much
pressure it can deliver. and whether it is adjustable.
If the thing will deliver enough fluid fast enough at high enough
pressure then I can use it. But what if the pressure is too high and
the unit doesn't have an adjustment? I should just be able to add my
own pressure regulator, right?
Thanks,
Eric