| 摘要 |
A hydraulic circuit for construction machines which, in order to prevent a vacuum phenomenon which occurs in the hydraulic pressure chambers of hydraulic actuators, such as hydraulic cylinders and hydraulic motors, is provided with a back pressure regulating valve in an oil passage for returning oil to an oil tank from a direction switching valve, with a make-up means to feed the upstream working fluid to the hydraulic pressure chamber, wherein problems such as increased loss of hydraulic horse power and decreased output from the hydraulic actuator, caused by increase in the back pressure in the return oil passage, are eliminated. A make-up hydraulic source feeding compressed hydraulic fluid to the make-up hydraulic passage connected to the hydraulic chamber is provided in other than the return passage to the oil tank, and the back pressure regulating valve in the return oil passage is omitted.
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