Patent ID: 7650907

Claim:
A hydraulic control apparatus for a single-action cylinder, comprising: a switch valve for controlling supply and drainage of a fluid with respect to the cylinder, the switch valve being switched among a supply position for supplying the fluid to the cylinder, a drainage position for draining the fluid from the cylinder, and a neutral position for preventing the supply and the drainage of the fluid with respect to the cylinder; a cylinder side passage connected to the cylinder; a switch valve side passage connected to the switch valve; a valve body accommodation chamber linearly extending between the cylinder side passage and the switch valve side passage, the accommodation chamber having a first end and a second end, wherein, in a portion corresponding to the first end, the accommodation chamber has a cylinder side opening that opens to the cylinder side passage, and wherein, in a portion corresponding to the second end, the accommodation chamber has a switch valve side opening that opens to the switch valve side passage; an on-off valve displaceably located in a vicinity of the first end of the valve body accommodation chamber, the on-off valve defining a first back pressure chamber in a vicinity of the first end, wherein the on-off valve is capable of shutting off a communication passage that extends from the cylinder side passage to the switch valve side passage through the valve body accommodation chamber; a flow control valve displaceably located in a vicinity of the second end of the valve body accommodation chamber, the flow control valve defining a second back pressure chamber in a vicinity of the second end, wherein the flow control valve is capable of shutting off the communication passage in accordance with displacement of the flow control valve; a partitioning member fixed in the valve body accommodation chamber, the partitioning member partly separates the on-off valve and the flow control valve from each other, wherein the partitioning member defines a third back pressure chamber, which is a back pressure chamber for the flow control valve; a first controller for controlling operation of the on-off valve, wherein, when the switch valve is at the neutral position or the supply position, the first controller causes a fluid pressure of the cylinder side passage to act on the first back pressure chamber, thereby urging the on-off valve in a direction for shutting off the communication passage, wherein, when the switch valve is at the drainage position, the first controller causes a first pilot pressure, which is lower than the fluid pressure of the cylinder side passage, to the first back pressure chamber; and a second controller for controlling operation of the flow control valve, wherein, when the switch valve is at the drainage position, the second controller causes a second pilot pressure, which is lower than the fluid pressure of the cylinder side passage, to act on the second back pressure chamber.