Model 621

SKU: 621

Flow Switch, Inline Body

The Model 621 Inline Flow Switch is equipped with a body that fits directly in, and becomes part of the pipeline. The inside body dimensions and end connections conform to those of the pipeline. These switches protect pumps, blowers, heat exchangers, etc. They are factory calibrated to switch at the specified flowrate. An internal adjustment allows small switchpoint changes to be made in the field. Large changes require changing the size of the paddle. Connection of the paddle to the output switch is done magnetically. A heavy-duty solid sealing tube separates the process fluid from the switch mechanism. Failures due to seal, diaphragm, and bellows leaks are eliminated. It features a full-bore body which mounts in pipeline; threaded, flanged, or butt weld pipeline connections, and recommended or general purpose service.

A pivoted paddle extends down into the flowing stream which creates a force by the flowing fluid as it strikes the paddle. At a predetermined velocity, the force becomes great enough to cause the target and the attractor to rotate about the pivot point. The magnet reacts to the new attractor position and the output switch operates. The target rotates back to its original position as the flow decreases, and the output switch then returns to its original. The 621 is built to ANSI, ASME, and PED specs.


  • Highly reliable magnetic design
  • Notifies user of flow or lack of flow
  • Multiple tee sizes available
  • Full bore body
  • Built to ANSI, ASME, and PED specifications


  • Style: Inline
  • Type: Paddle
  • Temperature: -4 °F to +400 °F (-20 °C to +204 °C)
  • Pressure: ≤ +2000 psi (≤ +137.9 ba
  • Actuation: ≥ 1.6 gpm (6.0 L/min)
  • Deactuation:≥ 1.3 gpm (4.9 L/min)
  • Accuracy: ≤ 10%
  • Output:SPDT or DPDT, 5 A
  • Available Wetted Materials:316 Stainless Steel, 416 Stainless Steel, brass, carbon steel Other materials available
  • Housing: Stainless Steel, aluminum
  • Process Connection:
  • Threaded:0.5 in to 4.0 in FPT
  • Flanged: 0.5 in to 4.0 in
  • Rating: ≤ 150 lb

Certifications & Approvals

  • Stainless Steel Housing Options Only: Third Party Listed by CSA NRTL/C (USA and Canada)

Required Ordering Information

  • Detailed model number
  • Detailed application number
  • Tag or nameplate detail (if required)
  • Documentation/testing tiers (if required, refer to Additional Resources in the product catalog)

Additional Information


Flow Switch, Inline Body

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