Put your email in your profile or in a post written out like "person AT blahblah DOT com" so I can send you a picture of a similar valve. That way we'll be sure to be talking about the same things.

The relief valve should be an allen headed screw (usually with an acorn cap nut on top) in the same spool that the pressure line goes into. Some older trucks also had a relief valve in the pump. (I can't remember if old Hysters had them or not)

If the relief valve on the control valve is the problem, you may be able to feel the oil rushing through the return line from control valve back to the sump.

If you're careful you should be able to remove and inspect the relief valve parts without a problem.

By the way, do NOT hook the pressure line directly into a gauge. This "dead heads" the pump and blows it up instantly.