Modern Cetop valve will have on the mounting flange four ports which will be marked P,T,A and B.
P = Pump (where fluid enters the valve,) T = Tank (the port from which fluid returns to the Tank or Reservoir) A and B are the two ports (A Port and B Port) normally connected to either end of a double acting Cylinder
The post relates to Crab Steering. Of you take a 3 position CETOPP spool valve, disconnect the pipes going to the two blue handwheel valves that select Four wheel steering and connect them instead to P and T, then connect A and B to either end of the rear steering ram. it should behave as follows;_
when Cetop valve is in centre position P, T, A and B are all closed off so no steering , the wheels wheel sare held wherever they pointed. (two wheel steering only)
If the Cetop is switched one way so that oil from steering circuit enters at P and is fed to one end of steering Cylinder via A port of the valve. Oil from the other side of the piston exits to port B and is fed back to the steering circuit through T port. Turn steering wheel the other way and the reverse happens. (contra steering)
If valve is switched the other way, oil entering from P goes to B driving piston in opposite direction, Oil on the other side of the piston now exits A and returns to the steering circuit via T. Turn steering wheel the other way reverses this action. (Crab Steering)