Open Center or Closed

Open center hydraulics is pretty much the norm. Easiest solution is to change out your two section valve for a three section and not worry about pump gpm. Prince hydraulics sell an assortment of universal valves for this type application and you can get change parts for detent or spring return spools.

From another website:

[indent]Q: What is a closed center or open center valve?
A: Open center refers to valves that allow oil to circulate at low pressure through the valve and back to the tank or reservoir when the valve is in the neutral position. Open center systems are normally used with a gear pumps…aka…if the engine is running, it is pumping oil. Closed center refers to valves that do not allow oil to flow through the valve when the spools are in the neutral position. The flow path is dead headed at the valve. Closed center systems are normally used with piston pumps or pressure compensated pumps. [/indent]

You can determine the flow by looking at the pump. It may have a tag or you may have to measure it. Like was said before, you can also go off the current valve and get something with similar sized ports and spools and you should be fine.

Also pay attention to where the relief valve is in the system. If it is in the current valve be sure your new valve has one as well and that it is set properly or you can destroy other parts of the system.