Parking brake assembly for railway vehicle brake system

A parking brake assembly for a railway vehicle brake rigging including first and second spaced-apart brake beams, first and second transfer levers pivotally connected at a point intermediate said ends thereof to a respective one of said first and second brake beams, first and second force-transmitting means interconnected between corresponding arms of said first and second transfer levers, a push rod secured at a first end thereof to a first lever arm of said first transfer lever and mounted for reciprocal motion within said brake system, said parking brake assembly comprising:

• (a) an elongated member, wherein the push rod is secured to one end of said elongated member;
• (b) a thread disposed on at least a portion of an exterior surface of said elongated member;
• (c) an actuator secured to an axially opposite end of said elongated member, said actuator responsive to supply of pneumatic fluid pressure to longitudinally move said elongated member in a first direction for increasing said length of said first force-transmitting means, to accordingly increase said spaced-apart distance between said first and second brake beams in order to apply a braking force, said actuator responsive to a loss of said pneumatic fluid pressure supply to longitudinally move said elongated member in a second direction to restore said length of said first force-transmitting means, to accordingly restore said spaced-apart distance between said first and second brake beams in order to release said braking force;
• and
• (d) a clamping means selectively operable for maintaining said elongated member moved in said first direction during loss of pneumatic fluid pressure supply to said actuator and for releasing said elongated member for movement in said second direction.