User's Manual for Model P7800 deadweight tester from April 2004 is below. P7800 deadweight testers are no longer available. The same model was sold as M3800 to 40000 psi (2500 bar) or M3820 to 60000 psi (4000 bar) also. Current models are the P3100 and P3800 deadweight testers.
These deadweight testers used a variable volume manufactured by Nova Swiss. There are about 6 screws on the underside that can be removed, then the internals of the pump section can be accessed. However, there are not user-serviceable parts inside the variable volume/capstan. In fact, there are pre-loaded shims, springs, etc. that are near impossible to put back in if disassembled. We do not offer maintenance service on these models and don't have any of the maintenance documentation.