A central tire inflation system (10) comprising a pressure relief valve (180) fluidly interposed control means (142, 156, 164, 154, 172) and a tire valve assembly (56, 58) is provided. The control valve assembly is effective to selectively pressurize or exhaust a first conduit (170) connected to a first port (178) of the pressure relief valve, a second conduit (50, 52) extends from a third port (184) of the pressure relief valve to the tire valve assembly and a second port (182) is connected to atmosphere. The pressure relief valve is effective to establish fluid communication between said first and second ports thereof when the pressure in said first conduit exceeds the pressure in said second conduit and to establish fluid communication between the second conduit and the exhaust port (182) if the pressure in said second conduit exceeds the pressure in said first conduit. The tire valve assembly is fluidly connected to a third conduit (68) fluidly connected to the interior pressurized chamber (74) of an inflatable tire (12). The tire valve assembly is effective in response to pressurization of the second conduit above a first reference pressure and pressurization of said interior chamber above a minimum tire pressure reference value to establish fluid flow between said second and third conduits.