JPS57129906A - Device for increasing pressure of fluid only at increase in load - Google Patents

Abstract

PURPOSE:To enable the adoption of a compact cylinder, by providing a device which is appropriate to the cylinder required to receive a high force at the time of initial motion or of compression near the end of forward movement and can generate a small amount of high-pressure fluid under heavy load and generate a large amount of low-pressure fluid under light load. CONSTITUTION:During the expansion of a cylinder 30, a heavy body 40 collides against an obstacle 50 so that the pressure of pressurized oil from an inlet port 1 rises. When the pressure has exceeded a set level, a changeover piston 7 is moved rightward against a spring 4 to open a drain circuit 18 to release the pressure of the space 15 on the front of a pressure increasing piston 3. As a result, the piston 3 is moved leftward due to the pressure difference between the front and rear of the piston and a check valve 11 opened by a rod 10 so far is closed. At the same time, the pressure of pressurized oil in the intermediate space 16 is heightened by the cross-sectional area difference between a rod 5 and a piston 6 to supply a small amount of high-pressure oil to the cylinder 30 through an outlet port 2 to drive the cylinder by high pressure.