Hydraulic cylinder assembly - has small dia. piston guided in bore of large piston, cooperating with two sprung latches

摘要

The cylinder provides a fast approach speed at low effort followed by a final low speed movement with a high effort to complete the working stroke. A small diameter piston and rod (2,5) are guided in the bore (3) of a large piston (4) which moves in the cylinder (6). The rod of the small piston passes through the end wall of the large piston andthorugh a gland in the cylinder. - Protruding into the bore of the large piston are two radial spring-loaded latches (9,10) which close behind the small piston when it reaches the bottom of the bore. The latches can be opened by pressure build up in passages (15,16) opening into the end space (1) of the cylinder. Pressurised oil drives the small piston downwards while the large piston is retained by the spring (17). Towards the end of its movement the small piston abuts against the bottom of the large piston and carries it downwards. At this point the two pistons move together at low speed with full hydraulic effort. In the reverse direction the latches (9,10) open hydraulically to allow fast return of the small piston.