PURPOSE: To prevent occurrence of cavitation due to shortage of fluid intake and erosion by directly returning the fluid being discharged from a fluid actuator into the first intake channel by a switching valve when the rotational speed of a pump becomes fast.
CONSTITUTION: When a pump 10 runs at more than an assigned high speed, the first port 56 of a switching valve 50 is connected to the third port 58, and the fluid discharged by a fluid pressure actuator 30 is sent directly into the first intake channel 63 through the second return channel 72. In this condition, the fluid discharged from the discharge port 11 of the pump 10 is wholly returned to the first intake channel 63 through a by-pass port 25 and the second return channel 72, and the whole amount discharge from the discharge port 11 is sent into an intake port 12. Consequently, shortage of intake fluid does not occur, thus avoiding occurrence of cavitation and also erosion and degraded durability of the pump's members due to said cavitation.
SAKAI TOSHIBUMI
KATOU TAKEYA
