System Sensor ST-3 Sampling Tube

The System Sensor ST-3 is a 3-foot metal sampling tube designed for HVAC duct smoke detection in air streams widths ranging from 2 to 4 feet. As a veteran-grade replacement for the L-307-1, this rugged cold-rolled steel component is essential for ensuring your InnovairFlex or legacy System Sensor DH100, DH200, DH400, and DH500 series detectors function according to code. When installing, always ensure the air inlet holes face directly into the airflow to maintain proper differential pressure across the sensor head. For any application exceeding 3 feet, remember that the tube must be supported at the opposite end of the duct to prevent vibration and ensure mechanical stability. This 36-inch tube provides the necessary coverage for mid-size commercial ductwork, meeting the NFPA 72 requirement for sampling tubes to extend across at least 2/3 of the duct width for reliable smoke detection.

Key Benefits for Contractors:

• Broad Compatibility: Seamlessly replaces the legacy L-307-1 and fits all System Sensor Innovair and InnovairFlex duct smoke detector housings.
• Field Serviceable: The 3-foot length can be cut down in the field to match specific duct dimensions, ensuring the sampling tube fits 24" to 48" spans perfectly.
• Durable Construction: Heavy-duty steel build stands up to high-velocity HVAC environments without the risk of melting or warping.
• Tool-Free Installation: Designed to lock securely into the detector housing with standard locking tabs for fast, reliable mounting.

Common Questions:

Can the ST-3 sampling tube be used in ducts narrower than 2 feet?
Yes, technicians can cut the ST-3 to the required length. However, for ducts 18 inches or narrower, the 1-foot ST-1 is typically the more efficient choice. Always verify that the tube covers at least 66% to 80% of the duct width to ensure UL 268A compliance.

Is an end plug required for this tube?
Correct. For the System Sensor ST-3 to create the necessary vacuum for air sampling, the end of the tube must be sealed with the red rubber stopper provided with the duct detector housing. Without a secure plug, the detector will not receive adequate air flow.

How do I verify the airflow direction for installation?
The tube is perforated with a line of sampling holes. These must face into the supply or return air stream. A simple visual check through the detector’s transparent cover or using a pressure gauge across the sampling and exhaust tubes will confirm correct orientation and sufficient air velocity.

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.