دیکشنری تخصصی مهندسی نفت - نسخه آنلاین

n: a form of sucker rod pumping unit in which the rotor is a chrome-plated steel external helix and the stator is a synthetic elastomer with a double internal helix permanently bonded into a steel housing. Rotation of the rods by a vertical spindle electric motor at dte surface causes the rods to stretch a predetermined amount to maintain the rod string in tension. It also causes a cavity containing well fluid to progress upward. The system is a rotary positive-displacement unit.