... transmission angle of the flexible rod deviates from 90°less than others, the pumping unit overcome the “dead ... . The beam swing angle can increase 30—50% than the conversional pumping unit 4.Two types of working ... clockwise, the up stroke crank angle is more than under stroke crank angle,it is the “slow ... anticlockwise, the under stroke crank angle is more than up stroke crank angle, it is the“fase ...