Description
McDonnell & Miller 120611 FS-251 Liquid Flow Switch
The McDonnell & Miller 120611, model FS-251, is a general-purpose liquid flow switch designed to monitor flow or no-flow conditions in piping systems.
The FS-251 uses an adjustable paddle-operated mechanism and SPDT electrical switch to provide an electrical signal when liquid flow reaches or falls below the selected operating point.
Typical applications include hot-water heating systems, boiler systems, pumps, liquid chillers and water-cooled equipment.
McDonnell & Miller 120611 Specifications
- Manufacturer: McDonnell & Miller / Xylem
- Part Number: 120611
- Model: FS-251
- Series: 250
- Product Type: General-Purpose Liquid Flow Switch
- Pipe Connection: 1" NPT
- Switch Type: SPDT
- Enclosure: NEMA 1
- Maximum Pressure: 160 PSI
- Maximum Fluid Temperature: 250°F
- Minimum Fluid / Ambient Temperature: 32°F
- Body Material: Brass
- Paddle Arms: Brass
- Paddle Material: Stainless Steel
- Seal: EPDM O-Ring
- Adjustable Flow Setpoint: Yes
- Weight: Approximately 1.9 lb
Included Paddles
The FS-251 includes stainless-steel paddles for multiple pipe sizes:
- 1"
- 2"
- 3"
- 6"
The proper paddle and adjustment setting depend on pipe diameter and required flow-switch operating point.
Electrical Ratings
The McDonnell & Miller 120611 FS-251 has the following motor-switch ratings:
- 120 VAC: 7.4A Full Load
- 120 VAC: 44.4A Locked Rotor
- 240 VAC: 3.7A Full Load
- 240 VAC: 22.2A Locked Rotor
- Pilot Duty: 125 VA at 120 or 240 VAC
- Frequency: 50/60 Hz
Typical Applications
McDonnell & Miller lists the FS-251 for applications including:
- Hot-water heating systems
- Hot-water supply systems
- Copper-tube boilers
- Pump systems
- Liquid chillers
- Water-cooled equipment
- Boiler flow proving
- Pump flow monitoring
How Does the FS-251 Work?
Liquid flowing through the pipe moves the installed paddle.
As flow changes, the paddle operates the internal SPDT switch. The switch can then be used to start or stop equipment or provide a signal to controls, alarms, burners, pumps or other devices.
Is 120611 the Same as FS-251?
Yes.
120611 is the McDonnell & Miller part number for the FS-251 general-purpose liquid flow switch with a NEMA 1 enclosure.
Customers may search for this product as:
- McDonnell & Miller 120611
- McDonnell Miller 120611
- 120611 Flow Switch
- FS-251
- FS251
- McDonnell & Miller FS-251
- Series 250 Flow Switch
What Is the Difference Between FS-251 and FS-254?
The major difference is the enclosure rating:
120611 / FS-251
- NEMA 1 enclosure
- General indoor applications
120610 / FS-254
- NEMA 4 enclosure
- Applications requiring greater protection from environmental exposure
Both are part of McDonnell & Miller's Series 250 general-purpose liquid flow-switch family.
What Size Connection Does 120611 Have?
The McDonnell & Miller 120611 uses a 1" NPT pipe connection.
The included interchangeable paddles allow the flow switch to be applied across several larger pipe sizes when installed according to McDonnell & Miller instructions.
Installation Note
McDonnell & Miller states that these liquid flow switches should not be used where liquid velocity exceeds 10 feet per second (3 m/s).
Flow-switch selection and adjustment should be based on pipe size, liquid flow rate and the required switch operating point.
Need Help Confirming the Correct Flow Switch?
Memphis Control Center stocks McDonnell & Miller flow switches, low-water cutoffs, pump controllers, water feeders and boiler-control replacement parts.
If you are replacing an existing FS-251 or another liquid flow switch, provide the model number, pipe size and application and we can help identify the correct replacement.
