| 摘要 |
PROBLEM TO BE SOLVED: To stably hold control pressure of an auxiliary cylinder regardless of change of an oil temperature by communicating first and second passages for communicating an upstream side and a downstream side of a throttle valve and two pressure chambers of the auxiliary cylinder, with each other through a communicating valve, and disposing an auxiliary relief valve on the second passage side. SOLUTION: In a load sensing control circuit for reducing a delivery quantity of a variable delivery pump P1 when rotating speed of a prime mover E is reduced, a throttle valve 15 is disposed in a delivery side pipe passage of a constant delivery pump P2. An upstream side and a downstream side of the throttle valve 15 and two pressure chambers of an auxiliary cylinder 10 for switching a regulator valve 5 are communicated with each other through first and second passages 16, 17. The first and second passages 16, 17 are communicated with each other through a check valve 20 as a communicating valve, and it is allowed that circulation is carried out only from the first passage 16 to the second passage 17. An auxiliary relief valve 18 wherein set pressure is set lower than cracking pressure of the check valve 20 is connected to the second passage 17 side. |
