Abstract: A seal system is provided for a reciprocating shuttle piston in a piston bore. An annular seal ring is fit to a piston ring groove in the piston. The seal ring is split along a cut extending entirely through a depth of the ring from a first side to a second side and entirely through a width of the ring from an outer peripheral seal face to an inner face. A fluid pressure differential across the seal results in a leak-by or metered flow of fluid across the seal, such as to equilibrate pressure across the piston. In one embodiment, the leak-by seal is fit to a groove in a shuttle piston of a pilot operated valve, the piston having a first face for opening and closing a main flow passage and a second face communicating with a pilot or backpressure passage. In one operation, the seal ring can bleed fluid from the second face for altering the pressure differential across the piston.