Valve Accessories Every Automation System Needs

1. The "Brain": Valve Positioners

A positioner is the microprocessor of the valve assembly. It compares the control signal from the Distributed Control System (DCS) or Programmable Logic Controller (PLC) to the valve stem's actual position and adjusts the actuator pressure to eliminate deviation.

Why you need it: Without a positioner, a valve suffers from hysteresis and sluggish response. For modern automation, Smart Positioners with HART, Profibus, or Foundation Fieldbus protocols are non-negotiable for predictive maintenance and diagnostics.

2. The "Eyes": Limit Switches & Proximity Sensors

While the positioner controls where the valve goes, the limit switch confirms that it got there. This feedback loop is essential for safety interlocks and sequence logic.

Why you need it: These provide the dry contact or proximity signal to the PLC, confirming "Valve Fully Open" or "Valve Fully Closed." In critical safety applications, you will require mechanically actuated switches over proximity types to avoid false signals due to electromagnetic interference.

3. The "Power Source": Actuators

Though often sold separately, the actuator is the most significant accessory. The type depends entirely on your site utility:

• Pneumatic Actuators: The industry standard for fire-safe and fail-safe operations.

• Electric Actuators: Preferred for remote locations lacking instrument air.

• Hydraulic Actuators: Used for high-thrust applications.

4. The "Shield": Solenoid Valves

For on/off applications, the solenoid valve acts as the pilot relay. It converts the electrical "open" or "close" command into pneumatic pressure to stroke the actuator.

Why you need it: In a fail-safe system, the solenoid valve is responsible for exhausting the actuator air supply to move the valve to its predetermined safe position (Open or Closed) during a power failure.

5. The "Air Supply": FRL Units (Filter, Regulator, Lubricator)

Instrument air is rarely "instrument grade" straight from the pipe. Moisture, particulates, and oil vapor will destroy a positioner's delicate I/P converter.

Why you need it: The FRL ensures clean, dry, and lubricated air enters the positioner and actuator, extending the lifespan of internal rubber diaphragms and O-rings by up to 300%.

6. The "Auxiliaries": Locking Devices & Indicators

• Manual Override: Allows operators to stroke the valve manually during instrument air failure or power outages.

• Visual Position Indicator: A simple "Open/Closed" dome or flag that allows field operators to verify valve status at a glance, bypassing the control room.

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