Imtex Controls: Actuating High-Performance Butterfly Valves

The demands for safety, efficiency, and environmental responsibility in the process industries have influenced the selection of pneumatic valve actuators for quarter-turn failsafe shutdown valves, such as ball and butterfly valves. In applications where space limitations and structural loads are concerns (such as offshore drilling & production platforms and FPSOs) many users opt for triple offset or high-performance butterfly valves instead of ball valves. However, for larger bore sizes (2 inches and above), the compact dimensions of butterfly valves, compared to ball valves, often result in smaller, weaker valve stems and lower Maximum Acceptable Stem Torque (MAST) values. 

To address these MAST issues, Imtex Controls has noted that many customers are adopting the Camtorc actuator design, especially for high-performance butterfly valves. The most commonly used actuators for automating on/off 90° valves utilise either rack and pinion or scotch yoke mechanisms. Rack and pinion actuators provide constant torque output throughout the stroke and are primarily used for smaller valves. In energy-related industries, where valves typically have higher torque requirements, the scotch-yoke system is often preferred. However, the piston design and torque curve characteristics of the scotch-yoke mechanism make it less suitable for spring return versions in failsafe applications when valves have relatively low MAST values. 

In conventional pneumatic scotch-yoke actuators, the air and spring sides are not independent. For the spring direction, the spring size must be large enough to ensure the valve closes with the specified safety margin. During the air stroke, the actuator air cylinder must not only generate sufficient torque to break the valve from its seat but also overcome the increasing spring force from the 0° (spring extended) to the 90° (spring compressed) position. This results in a large scotch-yoke actuator capable of producing high break torques at the maximum sizing pressure, potentially exceeding the valve’s MAST value. 

The Camtorc actuator overcomes this problem by using a cam mechanism in conjunction with a self-contained spring module. This design offers two primary benefits:  

1. Constant Torque Output: The mathematically derived cam profile maintains a constant Moment Arm throughout the actuator stroke, ensuring consistent torque for the full 90° travel.
2. Independent Spring Module: The self-contained spring module operates independently of the cam mechanism during the air stroke. A secondary air piston compresses the spring, providing the same constant torque output for both double-acting and spring-return versions.

 Additionally, the Camtorc actuator is typically smaller than comparable spring-return scotch-yoke actuators, offering space savings and reduced infrastructure costs.

Camtorc Range

Torque: Double Acting: 10 to 30,000 Nm / Spring Return: 10 to 20,000 Nm (Spring End).

Supply Pressure: Pneumatic Actuators: 2 to 10 barg / Hydraulic Actuators: Low - 3 to 10 barg / High - 10 to 210 barg / Optional – Higher pressure versions up to 400 barg available upon request.

Ambient Temperature: Nitrile Seals: -20°C to +60°C (T6); Viton Seals / -20°C to +130°C (T3) / EPDM 70 Seals: -40°C to +130°C (T4).

Certification / Approval: ATEX II 2 G Ex h IIC T* Gb / Suitable up to SIL 3.

*Refer to seals used for applicable temperature classes and ambient temperature ranges.

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