Compressed air from the tank is delivered through port 1 into cylinder 2 (see Fig. a) whose piston 3 is linked by tie-rod 4 to a lever mounted on the door. When compressed air is admitted by the door control valve to the right end of cylinder 2 through port 5, piston 3 is moved to its extreme left-hand position in which the door is closed. When the air is discharged from the right end of cylinder 2 through the door control valve, piston 3 is moved to its extreme right-hand position in which the door is open. Air admitted into the cylinder is divided into three streams. The first is admitted into the space in sleeve 6 through plug 7. When the air in the sleeve reaches a certain pressure, greater than in front of the plug, ball 8 closes the opening. This air cannot do any work because its pressure is the same in all directions on the cylinder walls. The second stream passes through channel a and applies pressure to piston 3. This pressure is negligible because of the small diameter of the channel. The third stream applies pressure to ring 9 and, compressing spring 11, is gradually admitted into the cylinder. As a result, the motion of the door begins slowly and gradually increases in speed. To regulate the speed of door motion, air is delivered from the control valve, not directly into the cylinder, but through special head 10, whose design is shown schematically in Fig. b. Admission of air from the valve to the cylinder is only along channel 12 through check valve 13 and air discharge is only along channel 14 through check valve 15. By means of regulating screws 16, which change the clear opening of the channels in the head, the velocity of air passage through the channels can be varied, thereby varying the speeds of door opening and closing independently of each other.
$4303$CHP,FD$