A service brake accelerator for indirect compressed-air brakes on railway vehicles includes a control piston which is loaded by the pressure in the main airpipe against the pressure in a reference pressure chamber and which controls a shutoff valve between the main airpipe and a piston chamber, a first outlet valve for the main airpipe and a second outlet valve for the piston chamber. Through appropriate dimensioning of the valve strokes (a,b), upon movement of the control piston out of its rest position the shutoff valve is closed first, and simultaneously or later the first outlet valve is opened and only subsequently the second outlet valve is opened. A valve piston arranged coaxially with the control piston is loaded by the pressure in the piston chamber and the force of a spring. On its other side, the valve piston is acted upon by the reference pressure over a partial area, but with the air vent valve open it is acted upon by the reference pressure over its entire area. When the piston chamber is vented, and after opening of the air vent valve, the valve piston rests against a valve stem connected to the control piston, thereby equalizing changes in loading with respect to the control piston.

A brake accelerator for drawing off air from the brake line of an air brake system for railway vehicles has a piston one side of which is subjected to air pressure in the brake line and the other side is subjected to a control pressure in an expansion chamber connected to the brake line through a throttle opening. A first valve is in a connection between the brake line and a pressure accumulation chamber connected to the atmosphere through a second throttle opening. The first valve is actuated by the first piston when the control pressure exerted on the first piston is predominant. A second valve opens subsequently to the first valve and is located in a connection leading from the expansion chamber through a throttle opening to the atmosphere. The second valve is actuated by a second piston loaded by the pressure in the pressure accumulation chamber in the direction to open the second valve against the force of a spring urging the second valve into its closed position.

A freight brake control valve device having an improved quick service function achieved by utilizing a common quick service volume during secondary quick service as well as preliminary quick service, in order to achieve an intensified secondary quick service reduction of brake pipe pressure. Further, a continuing local reduction of break pipe pressure is obtained without any time lag during transition from preliminary to secondary stage quick service. In a first embodiment of the invention, an exhaust passage separate from the brake cylinder exhaust passage is provided to assure venting of the preliminary quick service volume in the event the brake cylinder retainer valve is set up. In a second embodiment, the additional volume is vented via the brake cylinder exhaust passage.

A brake accelerator has a control chamber connected through a throttle orifice to a brake line. The brake system includes a control valve in which is an emergency brake piston one side of which is subjected to brake line pressure and the other side of which is subjected to pressure in the control chamber. The emergency brake piston, as a function of a pressure drop in the brake line, opens a brake line outlet valve so that air flows from the brake line through an inlet valve. The inlet valve is held by a control piston in its open position at the start of a pressure drop in the brake line and the air is flowed into a chamber to form a control pressure. The control pressure acts on the control piston to open an outlet valve for tapping or drawing off the air from the chamber and to close the inlet valve in such a manner that after a predetermined period of time when the pressure in the chamber has dropped below a predetermined value the control piston will be returned by a spring to its initial position so that a limited quantity of pressure fluid is drawn from the brake line by the accelerator.

A brake accelerator is operable sequentially upon each successive braking stage over the service application range of brake line pressure reductions and is employed with a single release brake control valve of an indirectly acting compressed air brake for railway vehicles. The control valve has a service brake portion and an emergency brake portion provided with a emergency brake piston one side of which is subjected to brake line pressure and the other side is subjected to auxiliary chamber pressure . The accelerator has a main piston which operates an inlet valve to connect the accelerator to the brake line. The main piston which is also subjected on one side to brake line pressure and the other side to auxiliary chamber pressure is moved to a service position upon an application of the brakes to open the inlet valve and connect a control piston with the brake line such that the control piston is subjected on both sides to brake line pressure. The control piston is repeatedly moved between two positions such that quantities of air are cyclically withdrawn from the brake line and the auxiliary chamber to maintain the pressure relationship existing on both sides of the main piston during the service application. The drawing off of air from the auxiliary chamber by the control piston is carried out separately and independently from venting of the auxiliary chamber by the emergency brake piston.