[chris deacon]

When you say a PVR valve i presume you mean a Pressure reducing valve? You will need a way to control this valve. Why do you want to get rid of the 4th valve may i ask?
Im not sure if you know how the 4th valve works on the 4200xl?
It opens when none of the hydraulics are being used to allow the oil thats not being used to go back to the tank. Then every time you use a hydraulic the 4th valve will close so all the oil can be used to move the rams. This 4th valve allows the pump and motor to last a lot longer. I might be telling you how to suck eggs here but i just thought i better make sure you understand what it is doing?