Spring return actuators use air pressure to open up and springs to close the valve (failsafe). Double performing air actuators use air to open and air to close. Ball check valves - a ball moves up and down inside the valve’s conically-shaped chamber letting ahead movement and sealing to halt https://edwineikll.laowaiblog.com/30052235/an-unbiased-view-of-brass-shut-off-valve