Description
The McDonnell & Miller FS251 (Part Number 120611) is a general purpose liquid flow switch engineered for reliable flow detection in hydronic, HVAC, and industrial piping systems. Featuring a 1″ NPT connection, this switch installs directly into the pipeline and uses a paddle-actuated SPDT (Single-Pole, Double-Throw) snap switch mechanism to provide precise flow/no-flow signaling for system protection and control.
The FS251 ships complete with four interchangeable stainless steel paddles — sized at 1″, 2″, 3″, and 6″ — allowing the unit to be configured for a wide range of pipe sizes and flow conditions right out of the box. The rugged NEMA 1 enclosure protects internal components in standard indoor environments, making it well suited for mechanical rooms, boiler plants, chiller systems, and similar applications.
Key Features
- General purpose liquid flow switch for hydronic and HVAC piping systems
- 1″ NPT pipe connection for straightforward inline installation
- SPDT snap switch action for reliable flow/no-flow control signaling
- NEMA 1 enclosure for indoor mechanical room environments
- Includes four stainless steel paddles: 1″, 2″, 3″, and 6″ sizes
- Stainless steel paddle construction resists corrosion in liquid service
- Versatile paddle selection accommodates a wide range of pipe sizes and flow rates
- Part Number: 120611
Specifications
- Brand: McDonnell & Miller (Xylem)
- Model: FS251
- Part Number: 120611
- Connection Size: 1″ NPT
- Switch Type: SPDT Snap Switch
- Enclosure Rating: NEMA 1
- Paddle Material: Stainless Steel
- Included Paddle Sizes: 1″, 2″, 3″, and 6″
- Application: General Purpose Liquid Flow Detection
Applications
- Hydronic heating and cooling systems
- Boiler and chiller plant protection
- Pump flow verification and interlock circuits
- Commercial and industrial HVAC piping
- Water-cooled equipment flow proving
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