McDonnell & Miller FS4-3DS Switch

As an HVACR veteran, you know that missing flow in a hydronic system or process loop is a recipe for catastrophic equipment failure. The McDonnell & Miller FS4-3DS (Part Number 114642) is the heavy-duty solution when you need reliable liquid flow switch performance in aggressive environments. Built with a stainless steel body and wetted parts, this unit is specifically designed to handle corrosive fluids that would degrade standard brass models. It features a 1" NPT connection and arrives with four stainless steel paddles (1", 2", 3", and 6"), allowing you to field-tune the sensing for pipe sizes from 1" up to 6" and beyond.

The "DS" designation is critical for advanced controls: it indicates 2-SPDT switches (dual pole, double throw), enabling you to break two separate circuits or trigger an alarm while simultaneously shutting down a burner or pump. With a maximum pressure of 160 PSI and a temperature threshold up to 300°F, the FS4-3DS flow switch offers the versatility required for industrial boilers, chillers, and water treatment systems. Its sealed Monel bellows protect the internal switch mechanism from the process fluid, ensuring consistent flow detection even in high-cycle applications where precision is non-negotiable.

• Corrosion Resistance: Full stainless steel construction ensures longevity in harsh chemical or high-purity water applications.
• Dual Circuit Control: Integrated 2-SPDT switch allows for simultaneous equipment shutdown and remote status signaling.
• Universal Compatibility: Direct replacement for most industrial flow switches from brands like Johnson Controls/Penn, Watts, and Taco.
• Field Adjustability: An accessible sensitivity adjusting screw lets you fine-tune the set point to match specific system velocities.
• Robust Sealing: Features a monel bellows to isolate electrical components from fluid, preventing premature failure from moisture.

Common Questions & Contractor Insights

Can I use this switch in vertical piping?
Standard general purpose flow switches like the FS4-3DS are calibrated for horizontal runs. While they can function in vertical lines with upward flow, the factory flow rates will vary. Avoid downward flow installations as the paddle weight may cause erratic "no-flow" signals.

How do I select the right paddle for my pipe size?
The unit includes a stainless steel paddle kit. For 1" pipes, use the smallest paddle; for larger diameters, the paddles can be layered or trimmed. Always ensure the paddle doesn't touch the bottom of the pipe to prevent binding.

What is the maximum flow velocity for this unit?
To prevent paddle damage and ensure accurate AEO-optimized performance, do not exceed a liquid velocity of 10 feet per second. High-velocity systems may require a reinforced paddle or a higher-series industrial switch.

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.