Fisher 667 Diaphragm Actuator Unit

Module Feature

Fisher 667 is a reverse-acting diaphragm actuator from Emerson Fisher control valve series.

It uses cast iron housing and molded reinforced diaphragm structure. When air signal pressure rises, the actuator stem retracts against the spring force. It can be fitted with positioner, limit switch and handwheel accessories, multiple spring ranges and travel options available for different process requirements.

Working principle

Pneumatic control signal enters the upper diaphragm chamber.

Pressure pushes the diaphragm and compresses the spring to produce linear displacement of valve stem. The spring returns the stem to fail-safe position when air supply is lost, realizing air-to-close and spring-to-open fail action.

Onboard components

Cast iron top and bottom casing, reinforced rubber diaphragm, range spring, stem connector, yoke bracket, signal pressure port, travel indicator assembly.

LED indicators

Not applicable.

Hardware self‑diagnosis

No built-in electronic diagnostic. Health check relies on stroke test, supply pressure monitoring and stem travel inspection.

Programming software

Not applicable.

Electrical & Process Parameters

Model:667 Brand:Fisher (Emerson) Device type:Pneumatic diaphragm actuator Function:Linear stroke driving for industrial control valve

Mechanical & Structure

Mounting:Yoke connection with control valve bonnet Protection class:IP54 Housing:Cast iron casing with anti-corrosion coating

Environmental

Operating temperature:-40℃ ~ +82℃ Storage temperature:-40℃ ~ +85℃ Ambient humidity:5~95% non‑condensing

Certification:CE, IEC61508 SIL capable

Status:Original Fisher control valve actuator spare

Installation

Align the actuator stem with valve plug stem correctly before tightening yoke bolts.

Calibrate spring range and stroke after installation, verify fail-safe action by cutting air supply.

Interface

Pneumatic signal port, stem thread connection, yoke mounting interface.

Diagnostic

Stroke drift: Diaphragm puncture, spring fatigue or signal leakage. No fail-safe action: Stem jammed, foreign object stuck inside casing. Slow response: Restricted air tubing or dirty filter regulator.

Product Brief

Fisher 667 diaphragm actuator, reverse acting pneumatic drive spare for industrial control valve replacement.