How to distinguish the pneumatic ball valve opening and closing
Pneumatic ball valve is composed of two parts: pneumatic actuator and ball valve. The pneumatic actuator is divided into two kinds of double action and single action, double action pneumatic actuator has gear rack, piston, output shaft, sealing ring and other parts. It and the ball valve form a double acting pneumatic ball valve, after the compressed air is connected, the air pressure drives the cylinder piston action, drives the output shaft to rotate 90 ° C, and the ball valve is opened or closed. When the air source is disconnected, there is no pressure in the cylinder, the output shaft stops rotating, and the ball valve remains in the open or closed position. Only after the air source is connected again, the action is resumed, so for the double-acting pneumatic ball valve, there is no difference between normally open and normally closed.
The single acting pneumatic actuator and ball valve constitute a single acting pneumatic ball valve. The difference between single-acting and double-acting actuators is that they are equipped with a return spring, and there is no return spring in the double-acting pneumatic actuator. When the air source is connected, the output shaft drives the ball valve to open or close. After the air source is disconnected, it is reset under the spring drive. The output shaft drives the ball valve to close or open.
Normally open pneumatic ball valve is to disconnect the air source, the ball valve is open, connected to the air source, the ball valve is closed. Normally closed pneumatic ball valve is to disconnect the air source, the ball valve is closed, connected to the air source, the ball valve is opened. Only single-acting pneumatic ball valves distinguish between normally open and normally closed.
The selection of normally open pneumatic ball valve and normally closed pneumatic ball valve is mainly to consider the production safety of process pipelines and equipment. When the air source fails, the pneumatic ball valve pipeline is opened or closed, and the safety impact on the system is different, so the normally open and normally closed mode of action of the pneumatic ball valve should be selected according to the actual situation.