A central tire inflation system for maintaining tire inflation on a vehicle is provided. The central tire inflation system includes a rotary union assembly having a housing that is coupled to and rotates with the hubcap. The housing is rotationally coupled to a stationary shaft. A flexible torque transfer shaft is connected to the stationary shaft on one end and to an axle plug on the other end. The axle plug has a hub forming, a bore where the hub is movable on a web of material. The flexible torque transfer shaft and hub have cooperative non-circular shapes to resist rotation. An air vent is provided in the rotary union assembly that is isolated from the lubrication area, which inhibits the pressurized air from the central tire inflation system from pressurizing the lubrication area.