Siemens Building Technology S55155-A108 Actuator

The Siemens S55155-A108 Actuator is the reliable professional-grade choice for terminal unit applications where fail-in-place functionality is a system requirement. Also known as the Siemens SSC131.09U, this electromotoric linear actuator serves as the direct SSC81U replacement, providing a seamless retrofit for legacy Siemite MT series valves. Operating on 24VAC, it utilizes a 3-position floating control signal to drive a 6.1 mm stroke with a nominal force of 67 lbf (300 N), making it a staple for maintaining precise temperature control in VAV boxes, fan coil units, and chilled ceilings. The non-spring return design ensures that should power be interrupted, the stem remains in its current position to prevent unnecessary system cycling. With an 88-second positioning time and a NEMA 2 enclosure, this unit is built for the rigors of commercial building automation environments. Installation is straightforward with a manual override and integrated LED position indicators, allowing for rapid commissioning on any 599 series Powermite valve.

• Direct Retrofit Compatibility: Engineered as the official administrative replacement for the Siemens SSC81U, ensuring zero-clearance issues with existing Powermite valve bodies.
• Precise Floating Control: The 3-position 24V control signal provides granular modulation for high-accuracy HVAC terminal unit performance.
• Fail-in-Place Security: The non-spring return mechanism maintains current valve settings during power loss, vital for protecting sensitive hydronic loops.
• Tool-Free Installation: Features a coupling nut for direct mounting to the valve bone, significantly reducing labor hours on multi-unit site installs.

Is the S55155-A108 compatible with older SSC81U installations?
Yes, the S55155-A108 is the designated functional successor to the SSC81U. It mounts directly onto the same Powermite 599 MT series valve bodies without requiring hardware modifications.

What happens to the valve position if the 24VAC power is lost?
This is a fail-in-place actuator. Unlike spring-return models that force the valve open or closed, this unit will hold the valve stem at its exact position at the moment of power failure.

Does this unit provide position feedback to the controller?
No, the S55155-A108 is a 3-position floating actuator and does not include an internal potentiometer or 0-10V feedback signal. Position is verified visually via the integrated LEDs on the housing.

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.