Hydraulic device to be connected in a pipe string

摘要

PCT No. PCT/NO97/00146 Sec. 371 Date Feb. 1, 1999 Sec. 102(e) Date Feb. 1, 1999 PCT Filed Jun. 6, 1997 PCT Pub. No. WO97/46787 PCT Pub. Date Dec. 11, 1997A vibration-generating device for a pipe string includes a hydraulic cylinder barrel, a hydraulic piston, changeover valves, and a double tubular piston rod. Each of the changeover valves is automatically shiftable. Fluid flows through the piston rod, changeover valves, and cylinder barrel.