| 摘要 |
PURPOSE:To improve driving efficiency of a pile and to produce a reliable pile- supporting force, by a method wherein, during accelerative drop of a hydraulic hammer, piston upper and lower chambers are intercommunicated, and during free drop of the hydraulic hammer, pressure oil from a hydraulic pump is communicated with an oil tank. CONSTITUTION:When a hydraulic hammer is acceleratively dropped, a switch 53 for selecting accelerative drop and free drop is opened, and oil in a piston lower chamber D is fed to a piston upper chamber U through lines 32 and 43, a valve 17, and lines 42 and 35. A part of pressure oil from a hydraulic pump 4 is fed to the upper chamber U through lines 30 and 43, a valve 17, and return passages 42 and 35, and the rest is fed thereto through lines 30 and 31, a valve 14, and lines 41 and 35, and simultaneously, pressure oil in an accumulator 5 is fed to the upper chamber U through a line 40. When a hydraulic hammer is freely dropped, the switch 53 is closed, and pressure oil from the hydraulic pump is fed to an oil tank 26 through a valve 7. |
