McDonnell & Miller FS1-J Switch

The McDonnell & Miller FS1-J (Part Number 113550) is a high-sensitivity in-line liquid flow switch designed for precision monitoring in systems with low flow rates. Featuring a 1/2" BSPT connection, this model is engineered for applications where early detection of flow or no-flow conditions is critical to protecting equipment like chillers or high-efficiency boilers. The snap-acting SPDT switch provides reliable electrical signaling, allowing for seamless integration into HVAC control circuits or safety interlocks. Built with a brass body and stainless steel internal components, the FS1-J handles a maximum liquid temperature of 225°F (107°C) and pressures up to 100 psi (7 kg/cm²). Technicians prefer this unit for its adjustable sensitivity, which permits fine-tuning the actuation point based on specific system requirements. Its compact footprint makes it an ideal solution for tight mechanical spaces where a standard paddle-style switch is impractical.

Key Benefits for Technicians:

• High Sensitivity Performance: Specifically calibrated for low flow rate detection, ensuring equipment protection in systems with minimal fluid movement.
• Versatile SPDT Switch: The single pole double throw configuration allows for simultaneous control of two separate circuits or signaling functions.
• Durable Construction: High-grade brass and stainless steel components provide corrosion resistance and long-term mechanical reliability in hydronic loops.
• In-Line Design: The 1/2" BSPT threading allows for direct installation into the piping run, reducing turbulent flow interference.
• Field Adjustable: Mechanical adjustment screw allows for on-site calibration to meet specific GPM (Gallons Per Minute) requirements.

Common Installation & Performance Questions:

What is the minimum flow rate required to actuate the FS1-J?
The FS1-J is designed for low-flow applications; the exact actuation point depends on the sensitivity adjustment, but it is engineered to respond to flow rates far lower than standard paddle-type switches.

Can this switch be installed in a vertical pipe run?
Yes, the McDonnell & Miller FS1-J can be installed in horizontal or vertical lines with upward flow. Avoid downward flow installations as gravity may interfere with the switch reset mechanism.

How do I adjust the sensitivity for specific system GPM?
Sensitivity is adjusted via the internal screw under the housing. Turning the screw clockwise increases the flow rate required to close the SPDT switch contacts, while counter-clockwise decreases it for finer sensitivity.

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.