AT Series Cylinder

Double-acting (standard) or spring-return (with spring cartridges)

10–5,000 Nm (AT05 through AT350 model sizes)

40–80 psi (2.5–6 bar)

90° quarter-turn rotation

ISO 5211 (mounting), NAMUR (solenoid/accessories)

Dual opposing pistons driving rack gears; central pinion gear produces 90° output rotation; constant torque across full stroke

Spring cartridges behind each piston (spring-return models); fail-safe positioning on air loss

Extruded aluminum body; hard anodized bore surface; bolted or threaded end caps; compact and lightweight

The Default Actuator for Quarter-Turn Valves

AT series is what you reach for when a butterfly valve or ball valve needs automation at moderate size. HVAC chilled water butterfly valves. Water treatment flow control ball valves. General process utility isolation. The AT series handles all of it — compact, light, affordable, and standardized enough that every accessory manufacturer builds NAMUR-mount hardware for it.

The rack-and-pinion mechanism is the core. Two pistons in a single cylinder barrel. Each piston drives a rack gear. The rack gears engage a central pinion. Air drives both pistons toward the center, the racks rotate the pinion 90°. Constant torque across the full stroke — rack-and-pinion geometry produces uniform rotational force regardless of pinion position. That constant output simplifies sizing. You pick the model that delivers torque above your valve's seating requirement, add a safety margin, and you're done. No torque curves to analyze, no breakout position calculations, no variable output to account for.

Aluminum Keeps the Weight Down

The extruded aluminum body is lighter than cast iron or steel scotch yoke housings by 40–60%. On a 12-inch butterfly valve mounted between flanges, actuator weight matters — a heavy actuator cantilevered off the valve body can distort the flange connection over time. The AT series keeps the total assembly weight within what the valve body and pipe supports handle without additional bracing.

The hard anodized bore surface protects the cylinder interior without adding weight. Piston O-rings ride on the anodized surface with low friction and long seal life. The aluminum housing corrodes less than painted steel in humid and mildly corrosive environments — water treatment plants, coastal installations, outdoor HVAC equipment. For aggressive chemical environments, specify optional coating or stainless steel variants.

NAMUR Means No Custom Brackets

The NAMUR interface on the actuator body allows direct mounting of solenoid valves, limit switches, and positioners. Standardized bolt patterns and air passage locations. No custom brackets, no adapter plates, no drilling holes in the actuator housing to fit a non-standard accessory. Every major accessory manufacturer builds NAMUR-compatible products. That interchangeability reduces procurement complexity and maintenance inventory — one solenoid valve design fits every AT series actuator in the plant.

Where AT Series Stops and Scotch Yoke Starts

AT series covers torque up to 5,000 Nm. That's adequate for butterfly valves up to about 12 inches and ball valves up to about 8 inches in moderate-pressure service. Beyond that size and pressure, seating torque exceeds what the AT series delivers at standard supply pressure. The scotch yoke takes over — its variable torque output produces higher breakout force for large valves. Don't stretch the AT series beyond its range. The actuator stalls on high-torque valves, and you're back to manual operation.

A: AT series for moderate-size quarter-turn valves where torque is under 5,000 Nm and seating/unseating differential isn't extreme. Scotch yoke for large valves (12+ inch butterfly, 8+ inch ball) with high breakout torque. If your valve datasheet shows seating torque that exceeds the AT series maximum for your supply pressure, you need scotch yoke.

A: Simplicity. You size for one torque value. The positioner sees consistent force conditions at every stem angle. Modulating control response is predictable. No torque curve to analyze. For most quarter-turn applications at moderate size, constant torque is all you need.

A: Yes, with the standard hard anodized finish. Aluminum anodizing resists UV, humidity, and mild corrosion. In salt-air coastal environments or chemical plant atmospheres with acid vapor, specify optional epoxy coating or the stainless steel variant. Don't assume bare aluminum survives aggressive exposure.

A: Yes. The constant torque output gives positioners consistent force conditions, which simplifies tuning and improves control loop stability. Pair the AT series with a NAMUR-mount pneumatic or electropneumatic positioner for throttling service. The compact accessory stack keeps the total assembly neat.

A: Spring cartridges sit behind each piston inside the cylinder barrel. When air supply is removed, the springs push the pistons away from center, rotating the pinion to the fail-safe position (0° or 90°). You select the spring cartridge set based on the torque your valve needs at the fail-safe end position — the spring force must seat the valve or hold it open against process pressure.