A pneumatic on-off valve is an industrial control valve that achieves rapid full opening or closing of the valve through a pneumatic actuator.

Working principle: Compressed air drives the actuator, and the valve reaches the fully open or fully closed position quickly through the movement of the piston or diaphragm. It is mainly used for the on-off control of pipelines and is usually equipped with an electromagnetic valve to control the air path.

1. Valve body:
   • Most commonly used: Pneumatic ball valve, pneumatic butterfly valve. Because both can be quickly opened and closed with a 90° rotation.
   • Others: Pneumatic gate valve, pneumatic globe valve, etc.
2. Pneumatic actuator:
   • Double-acting: Both opening and closing actions are completed by compressed air. When power or air supply is cut off, the valve remains in its original position.
   • Single-acting (spring return): One direction is driven by compressed air, and the other direction is reset by an internal spring. When power or air supply is cut off, the valve automatically returns to its initial safe position (fully open or fully closed).
3. Solenoid valve:

   Usually directly installed on the actuator as part of the "three-piece set" or installed independently.

   It is classified into single-coil control and double-coil control based on the number of coils.

   • Single-coil control: Changes direction when the coil is energized and returns to its original position by the spring when de-energized. Usually paired with single-acting actuators.
   • Double-coil control: Two coils, one for opening and the other for closing. Remains in its original position when the signal is lost. Usually paired with double-acting actuators.
4. Accessories (optional but important):
   • Limit switch: Used for remote feedback of the actual open and closed status of the valve ("fully open" and "fully closed" signals), and sent back to the PLC.
   • Air source treatment three-piece set: Filters (removes impurities), reduces pressure (stabilizes pressure), and lubricates (extends service life) the compressed air.
   • Manual operation mechanism: Allows manual operation in case of air loss or failure.

• Fast action speed: Compressed air driven, it opens and closes very quickly, especially suitable for applications requiring rapid cut-off.
• Relatively simple structure and high reliability: Pure mechanical pneumatic structure with low failure rate.
• Inherently safe and explosion-proof: The actuator itself has no electrical components, making it highly suitable for flammable and explosive environments such as oil and chemical industries.
• Strong load-bearing capacity: Can provide a large output force/torque.
• High cost-effectiveness: Compared with electric switch valves, it is more cost-effective in applications requiring explosion-proof and rapid action.

• Pneumatic on-off valves are widely used in all industrial fields where remote automatic shut-off or switching of flow paths is required.
• Batch processing: Automatically open or close different material pipelines in sequence.
• Safety interlock systems: Interlock with fire, leakage, and high-pressure alarms to cut off the source of danger in an emergency.
• Process switching: Switch flow paths between multiple production lines or different storage tanks.
• Equipment start-stop protection: Interlock with pumps and compressors, opening before startup and closing after shutdown.

Pneumatic switch valves are the "loyal guardians" that respond promptly on industrial automation pipelines. With the inherent safety of pneumatic operation, extremely fast action speed and high reliability, they have taken an absolute leading position in scenarios where rapid shut-off, safety interlocks and flammable and explosive conditions are required. Although they need a stable air supply, their simple principle, convenient maintenance and excellent overall performance make them one of the most classic and popular choices for achieving automated on-off control.