FIELD: pumping units. SUBSTANCE: end plates of cylinder have passages for connecting the pressure source pipe lines. Braking device is part of each cover. One cover is mounted for axial displacement relative to the cylinder for adjustment of the stroke and is provided with device for motion. Mounted in between passages and pipe lines are valves for adjusting the pipe line section which are fitted with shut-off members mechanically linked with movable cover of cylinder for reducing the passage area of valve in case of reduction of piston stroke. Mechanical linkage is made in form of cam secured on movable cover and linked with shut-off member of valve of lever engageable with cam. Device for motion of end plate is made in form of step motor. EFFECT: enhanced reliability. 3 cl, 1 dwg
