a rotative driver;

a housing coupled with the rotative driver;

a rod cover;

a moving unit that moves along a reciprocating path by a motion-converting mechanism between the housing and the rod cover;

a tubular piston rod coupled with the moving unit that includes a plug for coupling with a work piece;

the housing includes a first end damper that is comprised of elastic material for absorbing and impeding transient conditions of the moving unit that result from sudden applied forces that change in direction and magnitude a motion of the moving unit at a first end of the motion-converting mechanism, with the first end damper having a first end damper through hole;

the motion-converting mechanism converts a rotating motion of the rotative driver into a linear motion of the moving unit;

the motion-converting mechanism includes:

a feed screw for transmitting a rotative driving force of the rotative driver to the moving unit, the feed screw extending through the first end damper through hole;

the moving unit includes:

a piston;

a sliding nut coupled with the piston;

two annular piston dampers coupled with the sliding nut;

connecting member, and an annular member;

the piston is comprised of an axial through hole, with the through hole having a substantially elliptical cross-section;

the sliding nut is substantially cylindrical and is axially inserted in the through hole of the piston and includes a threaded hole that engages the feed screw, and further includes two flat outer surfaces to restrain the sliding nut from rotating relative to the piston;

the two annular piston dampers are fitted in annular recesses that are formed in axially opposite ends of the sliding nut;

the two annular piston dampers have axial lengths that are slightly longer than a length of the annular recesses, and have a substantially elliptical cross-section with substantially flat surface along a major axis and substantially circular along a minor axis of the substantially elliptical cross-section of the two annular piston dampers;

the connecting member is coupled between a front axial end of the piston and the tubular piston rod;

a first annular piston damper of the two annular piston dampers contacts with the connecting member, and a second annular piston damper of the two annular piston dampers contacts with the annular member;

the two annular piston dampers are comprised of elastic material that absorb and impede transient conditions resulting from sudden applied forces that change in direction and magnitude the motion of the moving unit along any section of the feed screw; and

the rod cover includes a second end damper that is comprised of elastic material for absorbing and impeding transient conditions of the moving unit that result from sudden applied forces that change in direction and magnitude the motion of the moving unit at a second end of the motion-converting mechanism.