Spring-applied brake unit for railway vehicle with manual release arrangement

A brake actuator for railway vehicles comprising:

• (a) a first cylinder;
• (b) a primary piston operably disposed in said first cylinder and subject to fluid pressure supplied thereto to effect operation of said primary piston in a brake application direction;
• (c) a second cylinder;
• (d) a secondary piston operably disposed in said second cylinder;
• (e) an actuator spring acting on said secondary piston to effect operation thereof in a brake application direction;
• (f) actuator rod means operable in response to said operation of either said primary and said secondary pistons in said brake application direction to produce braking on the vehicle, said actuator rod means comprising an actuator rod and means for adjusting the length of said actuator rod, said adjusting means including:
• (i) a screw-threaded, non-rotatable nut member having an externally projecting portion on which brake means may be mounted;
• and
• (ii) a screw-threaded spindle threadedly engageable with said nut member;
• and
• (g) means for normally locking said spindle against rotation to provide joint axial displacement of said spindle and said nut member in said brake application direction in response to said operation of either said primary piston and said secondary piston, said locking means being manually releasable to permit rotation of said spindle under the axial force of said actuator spring acting through said secondary piston during operation thereof, whereby said rotation of said spindle is in such sense as to decrease the length of said actuator rod.