Siebe AK-42309 Pneumatic Relay

The AK-42309-500 Positive Positioning Relay is a direct-action pneumatic relay that positions valve and damper actuators in precise response to controller pressure, enabling accurate mapping of control signals to actuator travel. It uses a pilot-operated, relay-type position-sensing mechanism with a large air capacity, and provides main-air and exhaust connections at the actuator location to speed response while offering an adjustable start-point and span for tuning actuator travel. The AK-42309-500 is compatible with a broad family of actuators, including MK-2690-0-0-1 and MK-2690-0-0-2, MK-3XXX, MK-44XX, MK-46X1-XXX-0-2, MK-48XX, MK-66XX, MK-68XX, MK-69XX, MK-7XXX, MK-88XX, and MK-89XX series; it cannot be used with M556, M573, M574, M693, MK-2690-0-0-0, MK-4600-0-0-0, MK-4600-0-0-1, or MK-12000 series actuators. Some installations use the AK-42309-500a variant with mounting linkage to ease mounting to compatible actuators. Originating from Siebe/Barber Colman lineages and later appearing in Schneider Electric catalogs, this relay remains a foundational option for positive-positioning control in HVAC applications, providing output-pressure changes aligned with controller pilot pressure to achieve faithful actuator positioning.