Schneider Electric (Barber Colman) MK4-3121 Actuator

The Schneider Electric MK4-3121 is a commercial-grade pneumatic damper actuator engineered for precise proportional control in complex HVACR systems. Designed as a direct successor in the Barber Colman lineage, this unit features a rugged die-cast aluminum housing and a high-performance beaded molded neoprene diaphragm for maximum durability. It operates within an 8 to 13 psi spring range and includes a factory-installed positive positioner (adjustable from 2 to 10 psi), ensuring the output shaft maintains an exact position relative to the control signal regardless of load variations or friction. The adjustable stroke, ranging from 2" to 4", allows for versatile application across various damper sizes and mixing box configurations.

For critical fail-safe requirements, the MK4-3121 utilizes an internal spring-return mechanism that automatically retracts the actuator shaft upon loss of supply air. This linear pneumatic actuator is rated for a maximum air pressure of 30 psig and features standard 1/8" FNPT air connections for seamless integration into existing pneumatic control loops. With its 8 in² effective area and capability for any-position mounting, this unit provides the reliable force necessary for managing airflow in air handling units and VAV terminals.

Key Benefits

• Precision Positioning: The integrated adjustable positive positioner compensates for stem friction and unbalanced loads for dead-on accuracy.
• Rugged Construction: Built with a die-cast aluminum body to withstand harsh mechanical environments without housing deformation.
• Fail-Safe Protection: Reliable mechanical spring return ensures shafts retract during pressure failure to protect system integrity.
• Field Flexibility: Features an adjustable stroke range and provides multi-position mounting to accommodate tight plenum spaces.
• High Temperature Resilience: Capable of operating in ambient temperatures ranging from -20° to 160°F (-29° to 71°C).

Common Questions

• Can the internal diaphragm be replaced if it leaks? Yes, the MK4-3121 is field-serviceable. Use the PND-2-1 replacement diaphragm kit to restore full pneumatic seal integrity.
• What is the purpose of the 2 to 10 psi positioner adjustment? It allows the technician to calibrate the start point and span, ensuring the actuator responds correctly to the specific output of your pneumatic controller.
• How do I adjust the stroke length? The unit features an internal stroke-stop. By adjusting this mechanism, you can limit travel anywhere between the 2" minimum and 4" maximum to match the damper's full-open/full-closed rotation.

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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.