Pressure cylinder with work stroke and fast approach stroke - has resistance valve allowing reversion to fast approach at any point of work stroke

摘要

Centrally behind the work cylinder is a smaller control cylinder, through which the pressure fluid is fed. The work piston has a backward extension which functions as piston in the control cylinder. The two sections are functionally separated by sealing rings. The fast approach piston works in an axial bore in the work piston. The bore continues, at reduced diameter, and ends in the control cylinder. A valve, controlled by the pressure in the control cylinder, opens or closes the fast approach cylinder. - When the fast approach piston finds no resistance the valve is open and the fast approach piston is moved forwards. Resistance to its movement generates increasing back pressure, which closes the valve and increases the presure in the control cylinder. When a threshold is reached, a second valve opens to admit fluid to the work cylinder.