it's possible that I'll buy a self contained air hammer (63kg ram weight), I don't know exactly it's condition. maybe there will be some parts to replace.
so, I start with the tup's seal (if i name it right), the rubber one. how could be replaced as there is no supplier anymore for replacements?
I think it could be (i don't know how's the shape yet) water-jet cut from some rubber sheet. is that a solution, and what kind of rubber is appropriate for that use?

Check out aleghany york, they do piston rings and seals. I bought a heavy cast piston ring for a hammer a year or so ago. They have all maner of stuff and may be able to make it or suggest someone who could.
http://www.alleghenyyork.com/

Is it rubber or leather. Some old machinery used leather for packing. I make leather packing for old water pumps for the gas engine guys.
Don't know about older air hammers.

Nazels use leather seals...

IIRC Grant and or Larry used plastic in one of theirs.

We really need more info. What is the make of the hammer? Are you talking about the seal between the piston and cylinder wall or the seal around the top cap, or a seal around the shaft on the bottom of the piston?

IIRC Grant and or Larry used plastic in one of theirs.

I seem to remember Grant did one with a polypack seal, maybe he took out the spring?

the hammer it's Romanian and I'm talking about a rubber seal that I was told that it's inserted in the flange (not sure if the term it's right) which is closing the cylinder and surrounds the tup at it's exit from the cylinder. so, that seal makes the exit of the tup air-tight. I'm searching for alternative solutions to that of making a mold and vulcanize it.

I came across the term "stuffing box packing" which I think describes the thing I'm talking about.

Does the leaking air effect the way the hammer runs? the only thing the leak there should do if it BAD is to not let the ram lift properly. Has nothing to do with hitting power, only lifting the ram.
It should be relatively simple to change it and probably a good idea to look inside the machine.

the hammer is not in running state, it's disassembled, I haven't seen it yet, but starting to think about most probable problems on it and the ways to solve them, to have an idea about. I was told that that seal might be one of the problems on old hammers and it's a part that has to be changed form time to time.

I've already seen two similar old and beaten hammers which were not holding the ram up properly on the idle and had oil leaking from the cylinder. I was told that's probably a seal problem (that seal I'm talking about). back in the times when that hammers were still produced, that was little problem, as the seals were available and cost almost nothing.

Matei ask on the Romanian knife makers forums, maybe someone knows where to repair pneumatic hammers, or where are the spare parts.