Rexroth spool valves are the directional valve control by the position of the spool, when the control oil pressure oil from the oil port of valve to the right into the slide valve right chamber, the spool is moved to the left pushed by the pressure, so that the pressure port P connected to the B , A to T port; or vice versa. Spool in both ends of the spring and the positioning sleeve back to the middle position if no pressure in the valve housing.