• SPECIAL TOPIC: CONTROL & SMART VALVES •
The Untapped Control Valve: Non-Lubri
How characterized plug trims, smart positioners, and proven sleeve-line technology bring modulating control capabilities to corrosive chemical services.
• By Arun Kumar Krishnan, Senior Engineer – Plug & Butterfly Valves – Flowserve Corporation
In chemical process plants, control valves regulate everything from acid flow rates to reactor feed ratios. For corrosive services involving hydrofluoric acid, chlorine, phosgene, and similar aggressive media, selecting the right control valve is a balancing act between corrosion resistance, emission containment, controllability, and cost.
Non-lubricated sleeved plug valves have been used in these environments for decades, mostly as on / off isolation devices. Criteria like PTFE sleeve sealing, constant operating torque, and zero lubrication requirements make them a reliable choice for aggressive chemical services.
What is less widely known is these valves are available with dedicated control plug trims, including V-port, sound trim, and linear configurations, enabling them to perform modulating duty in the same corrosive applications where they already serve as isolators.
This article looks at how these control trims, paired with modern digital positioners, extend plug valve capability into flow control service.
How Non-Lubricated Plug Valves Work
A sleeved plug valve uses a tapered or cylindrical plug that rotates 90 degrees inside a PTFE or fluoropolymer sleeve. The sleeve seals against the plug surface, eliminating the need for external lubricants. A fluoropolymer diaphragm serves as a secondary stem seal, and enhanced configurations are available that meet ISO 15848 and API 641 low-emission standards.
Since the plug rides on a self-lubricating polymer surface, operating torque stays relatively constant throughout the full range of travel, making actuator sizing straightforward and automated control more predictable.
Manufacturers offer both reducedport and full-area models. Full-area designs expand the flow passage, increasing the valve’ s flow coefficient( Cv) and improving its suitability for throttling duty. In-line seat adjustment can be performed under pressure without removing the valve from the line, cutting maintenance downtime considerably.
Characterized Plug Trims for Flow Control
What sets non-lubricated plug valves apart from simple on / off devices is the availability of purpose-built control plug trims, engineered to deliver specific flow characteristics when installed in place of the standard plug.
V-port plugs feature precision-drilled holes across the plug face. As the plug rotates open, the holes are progressively exposed to the flow path, producing a characteristic that approximates an equal-percentage curve.
The number, size, and arrangement of holes control the Cv at each increment of travel. Since equal-percentage is the preferred characteristic for most control loops, V-port plugs make the sleeved plug valve directly suitable for modulating service.
Soundtrim plugs use a similar multihole pattern but are engineered for noise attenuation. In high pressure-drop services where aerodynamic noise, cavitation, or flashing are concerns, the soundtrim plug breaks flow into smaller streams, reducing turbulence and noise. A self-cleaning design prevents particulate buildup.
A cutaway view of a non-lubricated sleeved plug valve showing the tapered plug, PTFE sleeve, and diaphragm stem seal.
Non-lubricated plug valves are widely used across chemical processing for their corrosion resistance and minimal maintenance requirements.
Linear plugs provide a proportional relationship between valve travel and flow, suitable for blending and dilution loops requiring a straight-line Cv response.
18 Valve World Americas | May 2026 | www. valve-world-americas. com