A decoking control valve comprising: a cylinder defining an inlet port and a plurality of outlet ports; ; a piston that moves along a direction of travel (T) within the cylinder and is configured to allow decoking fluid to flow in from an inlet port and out of a selective one of the outlet ports , thereby comprising at least three operating positions which result in fluid isolation of each port selectively in response to the piston movement; characterized by a plurality of hydraulic rod seals housed within a respective groove in the cylinder at each of the outlet ports and the hydraulic rod seals each comprise a seal ring which engages the piston , wherein: the distance by which the hydraulic rod seals are separated is such that the piston can only be engaged with a maximum of one of the hydraulic rod seals at a time; when in a first operating position the first outlet port is blocked with the piston being in place over one of the hydraulic rod seal such that the decoking fluid may flow in from the inlet port and out of the second outlet port and will not flow out of the first outlet port and when in another operating position the second outlet port is blocked with the piston being in place over one of the hydraulic rod seal such that the decoking fluid may flow in from the inlet port and out of the first outlet port and will not flow out of the second outlet port ; and the piston further comprising at least one drilled port which equalizes the pressure of the decoking fluid across the seal ring with the piston in a first position where the two ends of the drilled port on either side of the seal ring and seals the pressure of the decoking fluid across the seal ring with the piston in a second position with the two ends of the drilled ports entirely on one side of the seal ring . a cylinder defining an inlet port and a plurality of outlet ports; ; a piston that moves along a direction of travel (T) within the cylinder and is configured to allow decoking fluid to flow in from an inlet port and out of a selective one of the outlet ports , thereby comprising at least three operating positions which result in fluid isolation of each port selectively in response to the piston movement; characterized by a plurality of hydraulic rod seals housed within a respective groove in the cylinder at each of the outlet ports and the hydraulic rod seals each comprise a seal ring which engages the piston , wherein: the distance by which the hydraulic rod seals are separated is such that the piston can only be engaged with a maximum of one of the hydraulic rod seals at a time; when in a first operating position the first outlet port is blocked with the piston being in place over one of the hydraulic rod seal such that the decoking fluid may flow in from the inlet port and out of the second outlet port and will not flow out of the first outlet port and when in another operating position the second outlet port is blocked with the piston being in place over one of the hydraulic rod seal such that the decoking fluid may flow in from the inlet port and out of the first outlet port and will not flow out of the second outlet port ; and the piston further comprising at least one drilled port which equalizes the pressure of the decoking fluid across the seal ring with the piston in a first position where the two ends of the drilled port on either side of the seal ring and seals the pressure of the decoking fluid across the seal ring with the piston in a second position with the two ends of the drilled ports entirely on one side of the seal ring . <EOS>