Abstract: A pneumatic strut for use as an opening power assist mechanism for a motor vehicle tailgate has a piston rod extending from a piston contained within a cylinder. The piston separates the cylinder into two work chambers, each containing a gas charge under pressure. A bypass opening is active to connect the work chambers during the initial opening displacement of the tailgate to automatically open the tailgate through a first opening angle range. A second valve can be externally actuated to connect the two work chambers to further selectively open the tailgate into a second opening angle range. To close the tailgate, a third, directionally dependent valve can automatically connect the two work chambers during the closing displacement of the tailgate.