McDonnell & Miller FS4-3 Switch

For contractors requiring reliable system protection, the McDonnell & Miller FS4-3 (Part Number 114400) is a heavy-duty general purpose liquid flow switch designed to monitor flow in heating, cooling, and water process lines. This 1" NPT unit features a single pole, double throw (SPDT) configuration, allowing you to easily integrate signal lights, alarms, motors, or burners into the control circuit. Engineered to operate at a max pressure of 160 PSI and fluid temperatures up to 300°F, it is a versatile choice for commercial and industrial boiler water flow control.

The FS4-3 is a universal replacement for many legacy units, and is technically identical to the E-201-4 model. It comes equipped with four stainless steel paddles (1", 2", 3", and 6") to accommodate pipe sizes from 1" upwards. The internal sealed Monel bellows provide a dependable seal against the liquid stream, while the hardened stainless steel bearings reduce mechanical friction to ensure precise actuation at set flow rates. With dual electrical knock-outs and a high-accuracy sensitivity adjustment screw, this mechanical flow switch provides the field flexibility needed for rapid installation and troubleshooting.

Key Benefits

• Broad Compatibility: Serves as a direct universal liquid flow switch replacement for various models from Johnson/Penn, Taco, and Watts.
• Durable Construction: Features stainless steel paddles and anti-friction bearings for longevity in demanding hydronic environments.
• Flexible Wiring: The SPDT snap switch and dual knock-outs simplify field wiring for both start and stop operations.
• Adjustable Sensitivity: An internal screw allows for fine-tuning the flow switch sensitivity to meet specific system GPM requirements.
• High Temperature Rating: Suitable for systems with high-temperature fluid requirements up to 300°F.

Common Questions

Can the FS4-3 be used in vertical piping?
While designed for horizontal runs, it can be used in vertical pipes with upward flow, though field adjustment of the sensitivity screw may be required to compensate for paddle weight.

Is this switch suitable for potable water applications?
The FS4-3 is typically used in closed-loop hydronic or non-potable water systems. For domestic water, check local codes regarding lead-free requirements.

How do I adjust the flow rate set point?
Adjustment is handled via the internal sensitivity screw; turning it clockwise increases the flow rate required to actuate the switch.

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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.