Fisher Type 377 Pneumatic Pressure-Sensing Trip Valve
The Fisher Type 377 Trip Valve is a high-reliability pneumatic pressure-sensing switching device designed to control the fail-safe action of pneumatic piston actuators upon supply pressure loss.
- 10.3 bar (150 psig) Maximum Supply Pressure
- Cv 0.5 (Ports A to B, D to E) / Cv 0.6 (Ports B to C, E to F) Flow Coefficients
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- 1 YearWarranty
Product Overview
The Fisher Type 377 Trip Valve is a high-reliability pneumatic pressure-sensing switching device designed to control the fail-safe action of pneumatic piston actuators upon supply pressure loss. Manufactured by Emerson under the Fisher product family, this trip valve continuously senses main instrument air pressure and automatically forces the actuator into a predetermined safety state fail-up, fail-down, or lock-in-last-position whenever air supply pressure drops below an adjustable set point. Once supply pressure recovers above the trip threshold, the valve automatically resets, restoring standard pneumatic control without requiring manual intervention.
Engineered with a lightweight die-cast aluminium housing and a durable 25% mineral-filled thermoplastic polyester cover, the Type 377 combines structural strength with corrosion resistance in harsh industrial environments. A single Type 377 unit replaces complex multi-valve pneumatic switching circuits, significantly reducing piping requirements, fitting leak paths, and maintenance overhead. It is compatible with Fisher 480, 585C, 685, 1061, 1066, and 1069 piston actuators, making it an essential fail-safe control component in oil and gas refineries, petrochemical plants, power generation stations, and process automation safety instrumented systems.
Technical Specifications
| Specification | Value |
| Product Name | Pneumatic Pressure-Sensing Trip Valve |
| Manufacturer / Brand | Fisher / Emerson |
| Model Number | Type 377 |
| Device Type | Pneumatic Trip / Switching Valve |
| Housing Material | Die-Cast Aluminium |
| Top Cover Material | 25% Mineral-Filled Thermoplastic Polyester |
| Diaphragm & O-Ring Material | Nitrile Rubber (NBR) |
| Maximum Supply Pressure | 10.3 bar (150 psig) |
| Minimum Supply Pressure | 3.8 bar (55 psig) |
| Adjustable Trip Point Range | 2.8 bar (40 psig) to 72% of supply pressure |
| Reset Pressure | 12.5% to 33% above adjusted trip point |
| Flow Coefficients | Cv 0.5 (Ports A to B, D to E) / Cv 0.6 (Ports B to C, E to F) |
| Pressure Connections | 1/4 Inch NPT Internal (All ports) |
| Available Fail Modes | Fail-Up, Fail-Down, Lock-in-Last-Position |
| Operating Temperature Range | −40°C to +82°C (−40°F to +180°F) |
| Actuator Compatibility | Fisher 480, 585C, 685, 1061, 1066, 1069 & Bettis G-Series |
| Mounting Options | Manifold Mounted, Yoke Mounted, or Bracket Mounted |
| Hazardous Area Standards | ATEX Group II Category 2 Gas/Dust (Ex h IIC / Ex h IIIC) |
| Functional Safety Capability | SIL 3 Capable |
| Approximate Net Weight | 0.95 kg (2.1 lb) |
| Operating Medium | Clean, Dry Compressed Instrument Air |
| Condition | New |
| Warranty | 1 Year |
Key Features
Automatic pneumatic failure mode triggering for fail-up, fail-down, or lock-in-last-position
Automatic system reset once supply pressure rises above calibrated trip threshold
Single-valve manifold architecture replaces multi-component switching assemblies
Rugged die-cast aluminium body paired with high-impact thermoplastic polyester cover
Adjustable set-screw trip calibration ranging from 40 psig up to 72% of supply pressure
Large diaphragm sensing surface and minimal moving components for extended cycle life
Flexible field configuration allowing conversion between fail modes with minor tubing adjustments
Integrated standard 1/4-inch NPT pneumatic ports for simplified piping and installation
Certified for functional safety instrumented applications up to SIL 3 levels
Typical Applications
Emergency fail-safe trip switching for pneumatic piston actuators
Double-acting cylinder lock-in-last-position control loops
Compressor anti-surge and critical shutdown valve assemblies
Refinery, petrochemical, and chemical process safety instrumented systems (SIS)
Oil and gas extraction, offshore platform, and pipeline safety manifolds
Power generation boiler steam and turbine bypass control systems
Pneumatic valve actuator monitoring and pressure-loss protection skids
Shipping & Support
Fast dispatch – Australia & Worldwide Shipping
Technical assistance available
1-year warranty
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