Product Critical Technical Advantages
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Integral Mounting and Tubeless Design: The 657NS2 features a cast-in integral mounting pad that eliminates the need for traditional bolt-on brackets. When integrated with Fisher FIELDVUE™ instruments, the actuator utilizes an internal air passage. This tubeless design removes external components that are prone to damage or vibration-induced fatigue, which is essential for nuclear safety qualification.
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Rapid Response Dynamics: The pressure side of the diaphragm casing is designed with a shallow profile to minimize internal volume. This allows the 657NS2 to respond faster to pneumatic signal changes, enabling tighter control in high-speed thermal-hydraulic process loops.
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Linear Thrust and Molded Diaphragm: By utilizing a molded diaphragm that travels in a deep casing, the 657NS2 ensures that the effective area remains consistent throughout the entire stroke. This results in maximum thrust for its size and highly linear positioning, which is critical for accurate valve modulation.
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Rugged Seismic Stability: Constructed with thick-walled cast iron and steel, the 657NS2 offers superior structural rigidity. This heavy-duty build is specifically designed to provide increased stability and corrosion protection, ensuring the actuator performs reliably during and after seismic events.
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Versatile Configuration Options: Fisher provides a wide range of spring rates, travel stops, and manual operators (handwheels) for the 657NS2. This modularity allows the actuator to be customized for almost any safety-related control valve application within a nuclear facility.
Technical Specifications for Nuclear Service
| Feature | Details |
| Actuator Action | Direct-Acting (Air-to-Push Down) |
| Service Rating | Nuclear Service (NS2 Qualification) |
| Casing Materials | Heavy-duty Cast Iron and Steel |
| Mounting Type | Integral Pad (reduces part count) |
| Air Connection | Internal Passage (Tubeless) or External |
| Compatibility | Traditional bracket kits and FIELDVUE instruments |
Primary Applications in Nuclear Facilities
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Cooling Water Systems: Reliable throttling for reactor and auxiliary cooling loops.
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Steam Distribution: Precise management of steam flow for power generation and safety systems.
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Chemical Volume Control: Accurate dosing and volume management in nuclear processing.
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Safety-Related Isolation: Dependable on/off operation for critical containment barriers.
