Patent ID: 8439236

Claim:
A bridge breaker comprising: a casing; a rotatable inner ring which is provided in the casing; and a blade for bridge breaking which is attached to the inner ring; wherein: the casing has an inner surface including an inner groove, and a hole extending from an outer surface of the casing to the inner groove, the inner ring has an outer surface including an outer groove which is arranged to face the inner groove of the casing, thereby defining a space between the outer groove of the inner ring and the inner groove of the casing, balls are provided in the space defined by the inner groove of the casing and the outer groove of the inner ring, so as to rotatably support the inner ring in the casing, the balls are insertable into the space defined by the inner groove of the casing and the outer groove of the inner ring via the hole of the casing at assembly, a plug is provided to plug the hole of the casing, the bridge breaker further comprises seal rings which have a square sectional shape, and are provided in clearances between the inner ring and the casing, the casing and the inner ring have contacting surfaces in the clearances therebetween, the contacting surfaces being at a same horizontal level, the sealing rings have lower side surfaces which contact the contacting surfaces of the casing and the inner ring, and the sealing rings are depressed against the contacting surfaces of the casing and the inner ring by pressure of air or another gas introduced into the bridge breaker.