The BW Single-Cylinder Single-Acting Scotch-Yoke Pneumatic Actuator is a compact spring-return pneumatic actuator designed for quarter-turn valve automation and fail-safe operation. Featuring a variable-torque scotch-yoke mechanism, it delivers high torque at both ends of the actuator stroke, providing reliable breakaway and seating torque for demanding valve applications.
The actuator uses compressed air for one-way operation, while an integrated spring mechanism automatically returns the actuator to its predefined safe position when the air supply is lost. The compact aluminum alloy housing offers a good balance of strength, lightweight construction and corrosion resistance. The mounting interface complies with ISO 5211 standards for easy installation on rotary valves.
The BW series is available in two fail-safe configurations: Fail-Close (FC) and Fail-Open (FO). It is particularly suitable for small- and medium-diameter ball valves, butterfly valves and other quarter-turn valves requiring reliable fail-safe operation and safety interlocking.
BW Single-Cylinder Single-Acting Scotch-Yoke Pneumatic Actuator – Working Principle
Fail-Close (FC)：Compressed air enters through Port A, pushing the piston to the left, compressing the spring on the right and rotating the scotch-yoke counterclockwise to open the valve. When air supply fails, the spring resets automatically, driving the scotch-yoke clockwise to close the valve.
Fail-Open (FO)：Compressed air enters through Port A, pushing the piston to the right, compressing the spring on the left and rotating the scotch-yoke clockwise to close the valve. When air supply fails, the spring resets automatically, driving the scotch-yoke counterclockwise to open the valve.
A pneumatic actuator converts the energy of compressed air into mechanical motion, enabling the valve to open, close, or continuously modulate its position for reliable and automated valve control. For pneumatic actuator selection and procurement, please contact our technical team and provide the relevant operating parameters so that we can recommend the most suitable actuator model for your application. （Unit: mm）
| ize | Part No | L | L1 | L2 | L3 | L4 | H | Q | U | V | Q2 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 13 | XLX-B13-1 | 240 | 120 | 260 | 1120 | 848 | 37 | 200 | 125 | 62 | 175 | |
| 17 | XLX-B17-1 | 328 | 164 | 335 | 1500 | 1165 | 62 | 278 | 143 | 86 | 211 | |
| 20 | XLX-B20-1 | 373 | 187 | 389 | 1694 | 1337 | 92 | 372 | 165 | 100 | 240 | |
| 25 | XLX-B25-1 | 373 | 187 | 394 | 1760 | 1397 | 148 | 484 | 165 | 100 | 240 | |
| 28 | XLX-B28-1 | 436 | 218 | 438 | 2055 | 1655 | 163 | 534 | 202 | 118 | 264 | |
| 30 | XLX-B30-1 | 436 | 218 | 463 | 2082 | 1682 | 191 | 584 | 202 | 118 | 264 | |
| 35 | XLX-B35-1 | 474 | 237 | 460 | 2250 | 1794 | 200 | 645 | 225 | 148 | 350 | |
| 40 | XLX-B40-1 | 474 | 237 | 460 | 2275 | 1820 | 227 | 700 | 225 | 148 | 350 | |
| 50 | XLX-B50-1 | 710 | 355 | 633 | 2596 | 2572 | 225 | 760 | 390 | 960 | 360 | |
| 60 | XLX-B60-1 | 780 | 390 | 650 | 2940 | 2929 | 295 | 915 | 415 | 975 | 360 | |
| 70 | XLX-B70-1 | 780 | 390 | 650 | 3102 | 3095 | 37 | 1066 | 415 | 975 | 360 |
BW Single-Cylinder Single-Acting Scotch-Yoke Pneumatic Actuator — Key Advantages
Variable-Torque Scotch-Yoke Design for High Breakaway Torque：The single-piston scotch-yoke mechanism delivers an inherent variable torque profile with peak torque generated near the 0° and 90° stroke ends. This characteristic precisely meets the breakaway and seating torque demands of ball valves and butterfly valves. Compared with rack-and-pinion actuators of equivalent size, it effectively overcomes valve jamming caused by medium differential pressure.
Spring Return for Fail-Safe Operation & Process Interlock：Built-in spring return mechanism automatically drives the actuator to a predefined safe position upon air supply loss or pressure failure. Two fail-safe configurations are available: Fail-Close (FC) and Fail-Open (FO). It is widely deployed on process pipelines in chemical, energy and other industries requiring safety interlock to prevent process risks.
Compact Construction for Space-Limited Installations：Integrated single-cylinder layout delivers a compact overall footprint. The hard-anodized aluminum alloy housing achieves low weight with outstanding wear and corrosion resistance, balancing mechanical strength and lightweight performance. Ideal for small-and-medium-sized valves with constrained installation space.
Robust Transmission Structure for Extended Service Life：The scotch-yoke features large load-bearing contact surfaces to reduce contact stress and enhance mechanical impact resistance. Optimized lubrication for moving components minimizes friction and wear. Adjustable mechanical travel stops at both ends enable accurate positioning at fully open and fully closed positions for easy on-site commissioning.
Standard Universal Interfaces for Flexible Accessory Integration：Output mounting flange complies with ISO 5211 standard and accessory interface matches NAMUR specification. It can be directly fitted to ball valves, butterfly valves, plug valves and other quarter-turn valves. The actuator supports straightforward installation of solenoid valves, limit switches and valve positioners to realize remote automatic control and position feedback.
Proven Solution for Medium-Duty Operating Conditions：Engineered for small-and-medium-diameter valves under medium differential pressure. Widely applied in water treatment, HVAC systems, municipal pipelines and general chemical processes, delivering reliable automation solutions for applications requiring fail-safe protection.
