What Is a Pneumatic Valve?
The term pneumatic valve can refer to two different parts of an air-powered system. A directional control valve directs compressed air to an actuator or cylinder. A pneumatically actuated process valve uses an actuator to open, close, or position a valve in a pipeline. The air powers the actuator; the process valve controls a separate medium such as water, gas, or a chemical fluid.
In a common electrically controlled on/off ball or butterfly valve package, the path is: field pushbutton or PLC/DCS command → solenoid-operated directional valve → compressed air to the actuator → valve stem → process valve. The electrical command switches the air path; compressed air provides the force to move the actuator. The air circuit and the process flow path remain separate. A locally operated pneumatic assembly may instead use a manual air-control valve, and a modulating assembly may use a positioner.
How Does a Pneumatically Actuated Valve Work?
In a common electrically controlled on/off assembly, a solenoid-operated directional valve receives a compatible electrical command from a field pushbutton or PLC/DCS system. Its coil may be specified for 24V DC, 220V AC, or another voltage according to the control design. When the command changes, the solenoid valve switches the compressed-air supply and exhaust paths to the actuator. Air pressure moves the actuator’s pistons or diaphragm. The actuator then rotates or moves the process valve stem, changing the valve position and the flow through the pipeline. The electrical signal controls the switching; the compressed-air supply provides the operating force.
A quarter-turn actuator commonly operates a ball or butterfly valve. Other valve designs may require linear motion and a different actuator arrangement. The required air pressure and actuator size depend on the selected valve, its operating conditions, and the torque or thrust needed to move it.
Single-acting (spring-return) vs. double-acting. A spring-return actuator uses compressed air to move in one direction and a spring to return in the other. Depending on the valve and assembly, it may be configured for a specified fail-open or fail-closed position. A double-acting actuator uses air pressure for both directions. Do not assume that a double-acting assembly will return to a defined position if the air supply fails. Confirm the required fail action when selecting the complete valve package.
What Does the Directional Control Valve Do?
The directional control valve manages compressed air, not the process fluid in the pipeline. In an electrically controlled on/off assembly, its solenoid responds to an electrical command and switches the air supply and exhaust paths. This is the usual interface between an electrical on/off control circuit and the pneumatic actuator. If electrical on/off control is not required, a manual air-control valve can switch the air locally. Some designs use a moving spool; others use different internal mechanisms. Terms such as 3/2-way and 5/2-way describe the number of ports and switching positions in the air-control device. They do not describe the number of ports in the ball or butterfly valve that handles the process medium.
This distinction matters when reading a specification. A 3/2-way air-control valve may operate a spring-return actuator, while a 5/2-way configuration is often used with a double-acting actuator. The actual accessory choice must match the actuator and control circuit.
Main Parts of a Pneumatically Actuated Valve Package
- Process valve: The ball, butterfly, globe, or other valve body that controls the pipeline medium.
- Pneumatic actuator: Converts compressed-air energy into rotary or linear movement.
- Air-control device: For electrically controlled on/off service, a solenoid-operated directional valve switches the actuator’s air supply and exhaust in response to an electrical command. A local manual air-control valve or a positioner may be used in other control arrangements.
- Other accessories: An air filter/regulator, limit switch box, or manual override may be specified for the application.
How Do You Choose the Right Assembly?
Start with the process medium, pressure, temperature, valve size, and end connection. Decide whether you need local manual operation, electrical on/off control from a field pushbutton or PLC/DCS, or modulating control. For electrical on/off control, specify the solenoid valve’s coil voltage and the required air-switching arrangement; for modulating control, confirm the positioner and signal type. Then specify the available air supply, actuator action, desired position on loss of air, and any feedback or environmental requirements. A spring-return actuator must be sized for the valve and the operating conditions; adding a spring alone does not establish a suitable fail position.
If you are choosing a valve for a pipeline rather than a component that routes compressed air, explore our pneumatically actuated valve range. It includes pneumatic ball valves and pneumatic butterfly valves. Send us your operating conditions and required control action for a suitable assembly.
FAQ
How do pneumatic valves work? Compressed air moves an actuator, which opens, closes, or positions the process valve. In a common electrically controlled on/off package, a solenoid-operated directional valve responds to a field pushbutton or PLC/DCS command and switches air to and from the actuator. The electrical command controls the air path; compressed air supplies the force that moves the valve.
Does every pneumatic valve close when air is lost? No. A defined fail position depends on the selected actuator, spring configuration, valve assembly, and control circuit. Confirm this requirement before ordering.
Do I need a solenoid valve for every pneumatic valve? No. It is normally specified when an electrical on/off command needs to switch air to the actuator. For local manual pneumatic operation, a manual air-control valve may be used instead. Modulating control may use an electro-pneumatic positioner; confirm the complete control circuit for the application.
Is a pneumatic solenoid valve the same as a pneumatically actuated ball valve? No. The solenoid valve switches compressed air in the actuator circuit. The actuated ball valve controls the separate process medium in the pipeline.
