| 摘要 |
A pump jack for pumping oil and like wells having a polish rod extending vertically out of a well casing is provided including a frame adapted to fit over said well, a hydraulic cylinder depending from said frame generally coaxially of said polish rod, a piston movable in said cylinder and having an end engaging said polish rod, a source of high pressure fluid connected to said cylinder for raising said piston in the cylinder, dump means on said frame simultaneously discharging the raising fluid from said cylinder and by-passing fluid from said source of high pressure fluid to said source of fluid, means on said piston selectively actuating said dump valve from a first position where all fluid from the source of high pressure fluid is delivered to one side of the cylinder for raising the piston to a second position where all fluid from the source and from said one side of the piston is simultaneously returned to the source and to the other side of the cylinder whereby the piston and polish rod are successively raised and lowered vertically relatively to the cylinder.
|
