I found a hollow Enerpac 12kpsi portapower cylinder recently. I'm contemplating rebuilding it (now that I know how). It' looks a lot like a regular 4" cylinder, except the piston is hollow right through. The setups I can envision with this are all pretty contrived - what are these generally used for?
Clamping parts in a fixture for one..Instead of tightening a nut the cylinder is put between the clamp and nut, then extended to clamp the part. These are usually puck shaped and only a few inches thick, with maybe an inch of cylinder extension...
You can use it to pull a bushing out of a hole. In that case a piece of pipe (the bottom should have a shoulder that will take a piece of
2" pipe), and a bolt through with a washer on the bushing (make sure it's heavy duty). That's just one of the things they're great at.
The main use I have for it is for my puller setup. I have a large OTC puller setup with a large bearing separator. If you have a piece of threaded rod and nut to go through the cylinder then you have a instant adjustable anvil for pushing (the only real problem with these cylinders is that they have a short stroke, this makes up for that). I have a set of wings that screw to the thread on the front of the cylinder where my puller bolts go. This setup is great for pulling just about anything off of anything.
The simple fact is that the hollow ram cylinders with the right accessories can be the most versatile cylinders you've ever used. They can be used to pull or push in many different ways.
Things to keep in mind is that you will want a selection of 3/4" threaded rod and nuts to go with the cylinder. Be sure and buy the B7 or better grade rod. The grade 2 like you find at the home supply store will not hold up to 12 tons.
With a calibrated pressure gauge or electronic load cell and a central pull rod in the system, these are used to test the withdrawal resistance of concrete anchors and studs driven by powder actuated tools. If I remember correctly there are similar setups for field tensioning critical (large) bolts and possibly tensioning rebar or cable for prestress concrete structural members.