Since your pressure never get abouve 1200psi, this is where I would start looking for the problem. Possible causes.
1. Relief valve not set high enough. Try adjusting relief and see if your pressure setting goes up. If not, possible causes.
2. Pump bypassing internally, not allowing suffence pressure build up. The fact that it builds up to 1200psi suggests that the pump is indeed shifting from high/flow low pressure to low flow/high pressure since a two stage pump generally makes that shift at 600-900psi. Might want to try capping off a hydraulic line after pressure guage to deadhead fluid flow and see if the pump will actually build more than the 1200psi it is currently showing. If it wont, and adjusting relief doesnt help, then time for a new pump. If you do get a pressure build up. Next step
3. Valve could be bypassing , do same cap and deadhead of hydraulic line after valve and between cylinder. If you get more pressure build up, valve good, if not, replace or rebuild valve.
4. If pump and valve check out, time to take a look at the cylinder. If pressure is good at valve and pump, then it has to be bypassing thru the cylinder. You can fully extend or retrack the cylinder and unhook one hose, activate valve and see if fluid escapes from cylinder. Warning, make sure the hose you unhook is not the one that you activate pressure to, otherwise, big oil spray and mess. If cylinder is fully extended, the hose on the rod end of cylinder would be the one to unhook. If after applying pressure to opposite hose, oil flows out of rod end cylinder port, its a safe bet that the cylinder is bypassing and need rebuilt or replaced. If you get a big gush of oil out of cyl, it could be because you didnt have the cylinder fully extended, but that big gush of oil should stop pretty quick and either not flow at all or very little. If lots of oil keeps coming out, your cylinder is bad.
