Abstract: A hub cap for a wheel hub having a cylindrical housing with a closed first end and an open second end adapted for attachment in an air-tight sealing arrangement to the outer end of a wheel hub to form a closed air system in the interior of the wheel hub. An air pressure gauge in an air flow connection with the closed air system is operable to provide a visual indication of the air pressure in the closed air system. The air pressure gauge includes a dial face and a pressure indicating needle moving relative to the dial face in direct relation to the air pressure within the closed air system. The dial face includes indicia thereon to assist an observer to readily identify a breached seal condition within the wheel hub.

Abstract: A hub cap for a wheel hub comprises a cylindrical housing having a closed first end and an open second end, the open second being adapted for attachment in an air-tight sealing arrangement to the outer end of a wheel hub to form a closed air system in the interior of the wheel hub; an air valve in an air flow connection with the closed air system for receiving pressurized air; and an air pressure gauge in an air flow connection with the closed air system operable to provide a visual indication of the air pressure in the closed air system whereby a breached seal condition within the wheel hub can be detected. The second end is formed with a flange and an outer annular shoulder wherein the flange is adapted to fit into the outer end of a wheel hub. In a preferred embodiment, the flange is threaded for insertion into a threaded wheel hub. The outer annular shoulder includes an circumferential recess and an O-ring is disposed in the recess to provide an effective air tight seal.