Safety circuit for a working cylinder

Claim 1

In a safety system a working cylinder (2) having a double-acting piston (3) dividing said cylinder into a first (2a) and a second (2b) chamber on opposite sides thereof; first control valve means (13) for selectively supplying pressure medium from a source of pressure medium (21) to either side of said piston (3) for moving said piston (3) between a safety position on that side of said cylinder pertaining to said first chamber (2a) and an operative position on the opposite side of said cylinder; power means (10) disposed in said cylinder to bias said piston (3) toward said safety position; duct means connecting said first and second chambers; first valve means (33) in said duct means and including actuator means (34) communicating said chambers (2a, 2b) with each other in response to a safety signal; conduit means connecting said source of pressure medium and said first valve means; safety signal amplifying means (40) including a valve means and a signal responsive valve actuating means disposed in said conduit means to operate said actuator means to actuate said first valve means (33); passage means connecting said first chamber to said safety signal amplifying means; and automatic selecting means comprising a first non-return valve (50) in said conduit means and a second non-return valve (52) in said passage means selectively connecting said safety signal amplifying means (40) with said source of pressure medium (21) and with said first chamber (2a) respectively.