| 摘要 |
A bulk material pump device includes first and second hydraulic drive cylinders capable of causing alternate reciprocating movement of the corresponding pumping pistons to pump concrete contained in a hopper through a transportation conduit. The first drive cylinder has a cylinder housing whose bore is divided into a base chamber and a head chamber by a drive piston slidably received in the cylinder housing. The base chamber is in fluid communication with an oil pump while the head chamber is connected to the second drive cylinder. Under a loaded operation condition, a part of the pressurized oil in the base chamber is admitted into the head chamber via a head bypass line at the end of retracting movement of the drive piston and almost the same amount of the oil is returned back from the head chamber to the base chamber via a base bypass line at the end of extending movement thereof. Under an idle operation condition, the oil admitted into the head chamber is not returned back to the base chamber but, instead, will be drained to an oil tank by the action of a solenoid valve and a cartridge valve provided along a drain line.
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