A plurality of O-ring packings are mounted between ports in a spool valve bore. A valve spool is selectively shiftable in the bore for routing fluid among the ports and includes a plurality of lands, each of which, when located between a pair of ports, is seatingly engaged by one of the packings for preventing leakage between the pair of ports. Under normal operating conditions, the fluid pressures respectively existing at the pair of ports are different and this pressure differential exists across the packing. In order to prevent the packing from being dislodged from its mounting groove by fluid pressure, when the land portion is moved past the packing, a passage means located in the valve spool connects the fluid pressure at the port, away from which the land portion is moving, to the side of the packing remote from the port, to balance the pressure on the opposite sides of the packing, when the land portion is just about to move past the packing.
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