PURPOSE: To eliminate influence of external turbulence by furnishing a seat valve having a feedback slit at its outlet with a stem receiving the pressure with the same area, and connecting the oil pressure chamber and the outlet from a control pilot valve to a tank.
CONSTITUTION: A stem 3 is furnished at the outlet 5b from a seat valve 1A, and the section area of its flange part 4 is given the same area as the outlet pressure-receiving surface 30. The lead-in hole 5d of the oil pressure chamber 6A at the flange part 4 and the leadout hole 20b of a control pilot valve 20 are connected with a tank T through an oil pipe l2. When the load 25 varies and external turbulence occurs, a varying pressure is generated at the outlet 5b. As the output pressure-receiving area 30 and flange part 4 have the same area, this varying pressure is divided into two and impressed oppositely. Accord ingly the varying pressure (back pressure) is canceled, and no movement of seat valve 1A will be generated. Thus back pressure compensation is made in simple structure.
NOZAWA YUSAKU
YONETANI EIJI
NISHIMURA YOSHIZUMI
HITACHI CONSTRUCTION MACHINERY