Well since nobody answered my question I had to ask Google.
The 4 port 318 steering valve is a simple open center steering valve. If you use the return port to power a fown stream valve (a loader, remotes. 3pt) operation of the down stream valves will put the actuators in series with the steering cylinders resulting in loss of steering and/or down stream operation. It was and is a bad and potentially dangerous idea.
Because of that JD replaced the 4 port valve with a 5 port version. The 5 port valve incorporates a priority flow divider and steering vslve in a single housing. The flow divider section separates the inlet glow into two independent circuits. and isolates the steering flow from the downstream flow. The PS flow has prority and returns straight to tank. Any excess inlet flow is sent to the down stream valve.
If you connect the 5 port valve to a B8200 PS circuit you do not need or want the 5th port and if used it should return straight to tank. That effectively makes it a 4 port valve.
Now if you wanted to use a JD valve to add PS to a B7200 the opposite is true.
The B7200 does not have a built in priority valve of its own and you would need the 5 port steering valve. In this case you MUST move the selector valve on the tractors block to the loader position and use those two ports to connect the PS valve. Pump OUT on the tractor would go to pump IN on the steering valve, AUX out on the steering valve would return to implement return on the tractors block and PS out would return direct to tank.
Alternatuvely, if you had a 4 port steering valve you could use it and a standalone priority flow divider like this one to emulate operation of the 5 port valve.
Divider Valves,Hydraulic Valves,Hydraulics, PROPORTIONAL FLOW DIVIDER Brand new. Divides flow into two equal volume outputs regardless of load
www.surpluscenter.com
You would connect the IN port on the flow divider to pump OUT on the tractors block and connect the excess OUT port on the flow divider to the implement return port on the tractors block. The priority port on the flow divider would them feed the 4 port PS valve which would return straight to tank.
Dan