Control Valve

Overview

A control valve modulates process flow in proportion to a controller signal rather than simply opening or closing. The Pneumatic Actuator positions a plug inside the body to a setpoint commanded by a 4–20 mA loop, so the valve becomes the final element that the control system uses to hold a flow, level, pressure or temperature. This is a globe-style valve with a spring-and-diaphragm pneumatic actuator and a digital positioner, the standard configuration for continuous process throttling.

How it works

Flow turns through the cast Valve Body Assembly, a globe body and bolted bonnet that form the pressure envelope and carry the packing box. Inside sits the Valve Trim: a contoured plug, a characterized cage and a hardened seat ring. The cage guides the plug and its windows shape the equal-percentage flow characteristic, where each increment of travel changes flow by a fixed percentage, giving smooth control across a wide range. A PTFE V-ring packing stack seals the stem where it leaves the bonnet.

Above the body, the Pneumatic Actuator converts air pressure into linear travel: instrument air loads a molded diaphragm against a range spring, and the balance between them sets stem position. The valve is driven by a Digital Positioner, a microprocessor module that compares stem feedback to the command signal and meters air to the actuator through an I/P converter and pneumatic relay. Conditioned air is supplied through a Air Filter Regulator filter regulator, and a Handwheel Override provides manual override during commissioning or air failure. Body and bonnet joints are sealed by an O-Ring Set and assembled with a Fastener Set.