Pneumatic Centerline Butterfly Valve

2" - 24" (DN50 - DN600)

Cast iron (GG25), ductile iron (GGG40), A216 WCB, A351 CF8M

Resilient elastomer liner (EPDM, NBR, Viton, PTFE-coated) bonded to body bore—disc seals against the liner in both directions

Concentric (centerline) shaft alignment—shaft center, disc center, and body center all on the same axis. Pneumatic cylinder actuator (single-acting spring-return or double-acting), positioner optional for modulating control

API 609, MSS SP-67, EN 593

The Valve That Runs Your Plant's Basics

Water lines. HVAC chilled water loops. General process isolation where the media isn't hot, isn't abrasive, isn't corrosive enough to justify a high-performance valve. That's the territory where centerline butterfly valves live—and they live there because the geometry is simple and the economics are straightforward.

Concentric design means the shaft, the disc, and the body all share the same center axis. The disc rotates around its own center. When it closes, it presses into the elastomer liner bonded inside the body bore. The liner wraps around the disc edge 360°. That's bidirectional sealing built into the seat design—no preference for flow direction, no need to orient the valve based on pressure side.

You don't need triple offsets here. You don't need metal seating. The elastomer liner does the sealing work, and elastomer is forgiving—it deforms under disc contact, recovers when the disc opens, and keeps sealing after thousands of cycles in normal water and light-process service. EPDM for water and steam condensate. NBR for oil and fuel. Viton when you need chemical resistance. PTFE-coated liner when the process demands a harder surface with some elastomer compliance underneath.

Why Pneumatic Actuation Matters

Manual butterfly valves are fine for lines that get opened and closed a few times a shift. But process plants don't run on manual labor anymore. Sequence control. Remote operation. Automated isolation on interlock signals. These are the reasons you put a pneumatic cylinder on a centerline butterfly valve.

Single-acting spring-return actuators give you fail-safe positioning—spring closes the valve on air loss, which is the default for isolation duty. Double-acting actuators give you faster stroke speed and full control in both directions, which suits modulating service where the valve positions between open and closed. Add a positioner and you get proportional control—4-20mA signal drives the actuator to any angle between 0° and 90°. That turns a isolation valve into a control valve for flow regulation on water and HVAC lines.

The pneumatic package mounts directly to the valve body through a bracket and coupling. No linkage geometry, no external drive train. Compact, clean, and the actuator torque goes straight into the disc shaft.

Where Centerline Hits Its Limits

Let's be honest about what this valve doesn't do. The elastomer liner has a temperature ceiling—EPDM handles around 120°C continuous, NBR and Viton push higher but not past 200°C sustained. Abrasive media wears the liner. High-pressure differential across a closed centerline valve can deform the disc and leak past the liner. That's why pressure ratings stop at Class 150 / PN 10-16.

If your application exceeds those limits, you need a high-performance or triple eccentric valve. But for the majority of water distribution, HVAC, and general process isolation—where temperature is moderate, pressure is low, and media is compatible with elastomer—the pneumatic centerline butterfly valve is the most cost-effective automated quarter-turn valve available. No other automated valve type gives you bidirectional isolation at this price point with this installation simplicity.

A: Yes, with a positioner. The pneumatic actuator responds to a 4-20mA input signal and positions the disc at any angle between 0° and 90°. Centerline butterfly valves are suitable for modulating control on water and HVAC lines where precision doesn't need to match a dedicated control valve. If you need tight flow regulation, consider a globe valve instead.

A: Spring-return (single-acting) for isolation duty—valve fails closed on air loss, which is the safe default for process isolation. Double-acting for modulating service or applications where you need fail-open positioning. Spring-return costs less because you only need air supply on one side of the cylinder.

A: EPDM for water, steam condensate, and mild chemical service—compatible with most HVAC and municipal water applications. NBR for petroleum-based fluids, oils, and fuels. Viton for aggressive chemicals, higher temperature, and broader solvent resistance. PTFE-coated liner when you need a hard seating surface with elastomer backup compliance. Match the liner to your media, not to your budget.

A: Yes. The elastomer liner wraps the disc edge 360° and compresses equally regardless of which side the pressure comes from. No direction-dependent sealing, no need to orient the valve based on flow. Install it either way—sealing performance is identical.

A: Minimal. Clean, dry instrument air is the main requirement—moisture and particulate contamination degrade cylinder seals over time. Annual inspection of the positioner and supply air filter. The elastomer liner in the valve body has a finite service life—plan for liner replacement per your cycle count and media conditions, typically every 5-8 years in standard water service.