Schneider Electric (Barber Colman) MK-4821 Pneumatic Valve Actuator

The Schneider Electric MK-4821 is a professional-grade pneumatic valve actuator designed for the precise positioning of 1-1/2" to 2" VB-9XXX series globe valves in commercial HVACR systems. Built for the rigors of mechanical rooms, this actuator features a rugged die-cast aluminum housing and an 11 sq. in. effective diaphragm area. It operates on a proportional pneumatic signal with a nominal 8 to 13 psi spring range, ensuring reliable spring return action that retracts the shaft and raises the valve stem upon loss of air pressure. For contractors managing large-scale hydronic or steam systems, the MK-4821 actuator provides a stable 1-inch stroke and is rated for a 30 psig maximum air pressure.

Installation is straightforward for any veteran technician, utilizing a 1/8" FNPT side-located air connection and an adjustable start point (± 1 psi) to fine-tune the valve control response. The beaded molded neoprene diaphragm is fully replaceable, allowing for cost-effective field maintenance without replacing the entire unit. Whether you are performing a Barber Colman MK-4821 replacement or a new pneumatic valve actuator installation, this NEMA Type 1 rated component delivers the high-torque performance needed for large-bore VB-9XXX compatible valves.

• Precise Control: Features an 8 to 13 psi blue-coded spring for accurate proportional response in globe valve applications.
• Fail-Safe Operation: Mechanical spring-return design ensures the valve stem raises to the safe position during total air loss.
• Durable Construction: Die-cast aluminum housing and high-quality neoprene diaphragm withstand ambient temperatures from -20 to 220°F.
• Field Serviceable: The diaphragm and spring are easily accessible for actuator maintenance, extending the service life of HVAC pneumatic controls.

What valve series is the MK-4821 compatible with?
This actuator is specifically engineered for use with Schneider Electric (formerly Barber Colman) VB-9XXX series valves in the 1-1/2" to 2" size range.

Can the start point be adjusted in the field?
Yes, the actuator includes an adjustable start point of ± 1 psi (7 kPa) to ensure precise calibration with your controller's pneumatic signal.

What is the fail-safe manual position for this model?
The internal spring is configured to retract the actuator shaft, which raises the valve stem upon a loss of control air pressure.

This item is not eligible for free shipping.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.