[HayZee518]

the cylinder uses air to move a piston inside the cylinder. the rod connects to your door. a two way valve would be required. upon energizing it air would go into the cylinder extending the ram and with it the door. with no air supplied, air would exhaust out of the cylinder upon action by the counter weight pulling the door open. so the cylinder is set up into a fail safe open condition. the cylinder is supplied air to keep the door closed. to make the closing operation smooth a throttling valve for speed is used so air is supplied gradually not all at once. [flow control valve]