Gearbox hydraulic circuit

A gearbox hydraulic circuit is disclosed. The gearbox hydraulic circuit comprises a hydraulic pump (12) connected to a fluid reservoir (14) to generate a flow of pressurised fluid. A pressure circuit (16) is connected to the hydraulic pump to convey the flow of pressurised fluid and a pressure control valve (22) is disposed in the pressure circuit between the first line (18) and the second line (20) of the pressure circuit to maintain the pressure of the pressurised fluid in the first line. A shunt (28) is connected to the pressure circuit. The shunt being operable to route the flow of pressurised fluid from the first line to the second line to reduce the pressure in the first line.