Butterfly Valves with Pneumatic Actuator

Rotary Disk Valves with Specialist Pneumatic Actuator are butterfly-type valves equipped with a rotary pneumatic actuator of single or double action (models SC-RAT and SC-RST).

Types of Pneumatic Control for Butterfly Valves

Types of pneumatic control:

• The standard double-acting pneumatic actuator SC-RAT controls the disc rotation through air supply, and if pressure is lost in the pneumatic system, the valve remains in its last position. The advantage of this type of pneumatic actuator is the equal force during clockwise and counter-clockwise movement, and the absence of spring return resistance, which would otherwise require a more powerful pneumatic actuator for the rotary valve.
• The single-acting pneumatic actuator with a return spring SC-RST can either fully close or open the butterfly valve when the air pressure in the control line is released. This is necessary for safety but requires using twice as powerful actuators.

Pneumatic control is performed by supplying compressed air under pressure up to 8 bar using a 5/2 Namur pneumatic distributor, which can be attached to the body of the rotary actuator.

Butterfly Disk Valves: Design and Working Principles

Butterfly valves are compact devices, the main element of which is a rotary disc fixed on a shaft. They derive their name due to the resemblance of their working mechanism to the movement of butterfly wings (from the English butterfly).

Structurally, the valve consists of a body, a disc, a shaft, and a seal. The body is usually made of cast iron, steel, or other materials depending on the operating conditions. Disc material options include stainless steel, cast iron with different coatings, and custom polymers. The choice of material depends on the medium's aggressiveness, temperature, and pressure in the system.

The operation principle of the valve is quite simple: when the shaft turns 90°, the disc rotates from the “closed” position (perpendicular to the flow) to the “open” position (parallel to the flow). The seal between the disc and the body ensures tightness in the closed position. Elastomer seals (EPDM, NBR, PTFE) or metal seals for high-temperature applications are commonly used.

Advantages of Butterfly Valves

Rotary disk valves have gained wide popularity due to several significant advantages:

• Compact design that saves space during installation
• Lightweight compared to other types of valves
• Quick opening/closing (rotation on only 90°)
• Low hydraulic resistance in the open position
• Flow regulation capability
• Simple maintenance
• Relatively low cost

Butterfly Control Systems with Positioners

For precise adjustment of the position of the rotary butterfly valve with a pneumatic actuator, single- and double-action positioners are used. A positioner is a device that, based on an input control signal, ensures the appropriate position of the actuator. In modern automation systems, positioners with a standardised control signal of 4-20 mA are the most common.

The operation principle of such a positioner is as follows: changes in current from 4 to 20 mA are converted into a corresponding change in air pressure supplied to the pneumatic actuator. Here, the 4 mA value typically means the valve is fully closed, and 20 mA – the rotary valve with a pneumatic actuator is fully open.

Modern positioners have the following functions:

• Conversion of an electrical signal into a pneumatic one
• Allows precise positioning of the rotary valve with a pneumatic actuator according to the control signal
• Compensation for friction and hysteresis effects
• Diagnosis of the actuator and valve condition
• Feedback on the current position of the shut-off element
• Adjustment of regulation characteristics

Where Can Rotary Disk Pneumatic Valves Be Used?

Systems with rotary disk valves and pneumatic actuators find application in various industrial fields:

1. In water supply and sewage systems
2. in the petrochemical industry
3. In the food industry
4. In energy (thermal power plants, boilers)
5. In ventilation and air conditioning systems
6. In the pharmaceutical industry
7. In the paper and pulp industry

The systems are especially effective where remote control, automation of technological processes, rapid flow switching, or emergency shut-off is required.

Conclusion on Pneumatic Rotary Valves

The rotary disk valve with a pneumatic actuator is an optimal solution for flow control in industrial systems. Their compactness, reliability, and automation capability make these devices indispensable in modern manufacturing. The wide range of materials – stainless steel and cast iron – aids in selecting the optimal solution for your environment. The choice of a specific type of pneumatic actuator – single or double action – depends on the specifics of use and the safety requirements of the system. Using positioners with a 4-20 mA signal allows integration of these devices into modern automation systems, providing high precision in flow regulation and increasing the efficiency of technological processes.