The Bendix+ R-12DC+ relay valve with biased double check valve functions as a relay station to speed up the application and release of the brakes in an air brake system. The valve is normally mounted at the rear of the vehicle in proximity to the chambers it serves. The valve operates as a remote controlled brake valve that delivers or releases air to the chambers in response to the control air delivered to it from the foot brake valve or other source. Most parts are interchangeable between the R-12+, R-12DC+, and R-14+ valves with the exception of the detail components of the valve covers. Bendix+ relay valves make extensive use of non-metallic internal components. For ease of servicing, the inlet/exhaust valve can be replaced without the need for line removal.