A release graduating valve for freight brake control is provided for a railcar having a pneumatic control valve, emergency and auxiliary reservoirs each normally charged with pressurized fluid from a brake pipe and a fluid pressure activated brake cylinder device for applying the brakes on the railcar. A selectively operable release graduating valve can include a graduated release valve and a changeover valve which selectively interposes the graduated release valve to exhaust brake cylinder pressure in a graduated manner responsive to brake pipe pressure. Alternatively, the changeover valve can isolate the graduated release valve and direct the pneumatic control valve to exhaust brake cylinder pressure in a conventional manner. The changeover valve can be operated responsive to the pressure in an air pipe supplied with pressurized fluid from a remote source. A permanent release graduating valve can be provided wherein the changeover valve is omitted, in which case the brake cylinder exhaust is always controlled by the graduated release valve. Either configuration of the release graduating valve could be also be utilized in an ECP freight brake control system.
A pneumatic emergency brake release timer comprises a high capacity transfer valve, a timing reservoir in communication with the pilot port of the high capacity transfer valve, the check valve and choke circuit providing parallel connections between the main source of pressure and the reservoir through a check valve and opposite flow through a dissipating choke.
