What is a Pneumatic Valve?
A pneumatic valve is a valve driven by compressed air. When purchasing pneumatic valves, specifying the size, type, and working pressure usually meets the procurement requirements. These valves can control various fluids, including air, water, steam, corrosive media, slurry, oil, liquid metals, and radioactive media. However, this approach is incomplete in the current market economy. To stay competitive, manufacturers often make unique innovations within a unified pneumatic valve design concept, establishing their own standards and product features. Therefore, it’s crucial to provide detailed technical requirements during the procurement process and coordinate with the manufacturer to reach an agreement. This can be used as an appendix to the pneumatic valve purchase contract. This type of valve is typically installed horizontally in piping systems.

Compressed air pushes multiple sets of pneumatic pistons within the actuator, transmitting force to a crossbeam and internal curved track, which in turn rotates the hollow main shaft. The air supply distributes compressed air to each cylinder, changing the direction of the main shaft's rotation by adjusting the air inlet and outlet positions. The number of cylinders can be adjusted according to the torque requirements of the load (the valve) to operate the load.

A two-position five-way solenoid valve is commonly paired with a double-acting pneumatic actuator. The two-position design allows for two controllable positions: open and close. The five-way design has five air passages—one connected to the air supply, two connected to the external air chambers of the double-acting cylinder, and two connected to the internal air chambers. The specific operating principle can be referenced from the double-acting pneumatic actuator's working principle. With the increasing variety of control methods, there are now many ways to control pneumatic actuators in industrial production and control. The commonly used methods include the following.

A pneumatic ball valve consists of two parts: a cylinder and a ball valve. The cylinder acts as a driving component, with the output shaft providing power to rotate the ball valve core, thus enabling functions like switching, flow regulation, and direction control in the pipeline. Examples include the pneumatic O-type shut-off ball valve, pneumatic V-type control ball valve, and pneumatic three-way directional ball valve. Common accessories include solenoid valves, limit switches, filter regulators, and electric valve positioners. Pneumatic ball valves offer low flow resistance, a compact structure, good sealing, and a wide range of applications.

Ball Valves

Pneumatic V-Ball Valve

A. Applications
The pneumatic V-ball valve has a right-angle rotary structure and is used in conjunction with a valve positioner to achieve proportional control. The V-shaped valve core is most suitable for various control applications. It has a large rated flow coefficient, wide adjustable range, good sealing performance, zero sensitivity in adjustment, small volume, and can be installed vertically or horizontally. It is suitable for controlling gases, steam, liquids, and other media.

B. Features
The pneumatic V-ball valve is a right-angle rotary structure consisting of a V-shaped valve body, pneumatic actuator, positioner, and other accessories. It has an inherent flow characteristic close to an equal percentage. The valve uses a dual-bearing structure, resulting in low starting torque and good sensitivity and response speed. It also has an extremely high shearing capacity.

C. Pneumatic Piston Actuator
The pneumatic piston actuator uses compressed air as the power source. The movement of the piston drives the lever arm to rotate 90 degrees, causing the valve to open or close automatically. The components of the actuator include an adjusting bolt, actuator housing, lever arm, cylinder body, cylinder shaft, piston, connecting rod, and universal joint.

D. Working Principle of the Pneumatic Control Valve
A pneumatic control valve consists of an actuator and a control mechanism. The actuator is the thrust component of the valve, generating corresponding thrust based on the control signal pressure, driving the control mechanism to operate. The valve body is the control component, directly in contact with the regulating medium, and it adjusts the flow of the fluid.

 

Pneumatic Ball Valve
Pneumatic ball valves are classified into two types based on the cylinder operation method: single-acting cylinders and double-acting cylinders. Common types of cylinders include AT cylinders, GT cylinders, AW cylinders, etc.

A single-acting cylinder contains a return spring. The air pressure from the air source enters the cylinder through a solenoid valve, driving the piston to move. At the same time, the piston compresses the spring to store energy. After the solenoid valve releases the air pressure from the cylinder, the spring pushes the piston, causing the ball valve’s core to automatically reset, maintaining either the open or closed position.

Pneumatic Actuator

Double-Acting Cylinder
A double-acting cylinder does not have a return spring. It relies on the solenoid valve's electrical signal to switch the direction of the air supply, enabling the cylinder to perform reciprocating actions and drive the ball valve to open or close.

Differences between Single-Acting and Double-Acting Cylinders:

• Presence of Return Spring: A single-acting cylinder contains a return spring, while a double-acting cylinder does not.
• Solenoid Valve Configuration: A single-acting cylinder is equipped with a two-position, three-way solenoid valve, whereas a double-acting cylinder is equipped with a two-position, five-way solenoid valve.

Air Cylinders

• Cylinder Size for Same Diameter Ball Valves: A single-acting cylinder not only needs to account for the ball valve torque and medium pressure, but also the force exerted by the return spring. Therefore, the cylinder diameter must be larger. A double-acting cylinder, lacking a spring, has a smaller diameter when paired with the same size ball valve.
• Manual Switch Mechanism: In a single-acting cylinder, the manual switch mechanism must generate more torque than in a double-acting cylinder, as it needs to overcome the force exerted by the spring. In a double-acting cylinder, the torque required is smaller because there is no spring.
• Functionality: A single-acting cylinder can automatically reset the ball valve to a certain state (open or closed) when there is a failure in the air supply or when air pressure is lost. This is crucial for the safety of production processes, as the valve's position must be maintained. In this case, a single-acting pneumatic ball valve with a manual switch mechanism should be used. A double-acting pneumatic ball valve, on the other hand, is more suitable for applications where the open/closed position is not critical to production safety.
• Cylinder Output Torque Curve: In a single-acting cylinder, the output torque gradually decreases as the output shaft rotates due to the spring's action. The minimum torque still needs to be sufficient to drive the ball valve's core. In a double-acting cylinder, the output torque remains constant along a straight line and increases with higher air supply pressure.
• Cost of Cylinder: For cylinders with the same bore size, a single-acting cylinder has a higher cost due to the need for a return spring. A double-acting cylinder is generally less expensive.