Series TDFS2 Thermal Dispersion Flow Switch

Product Applications

  • Boiler flow proving
  • Hot water heaters
  • Chillers
  • Liquid transfer systems


The Series TDFS2 Thermal Dispersion Flow Switch is a thermal flow switch that indicates whether the flow rate is above or below a user set flow rate. The unit incorporates two LED status indicators providing visual switch indication. The set flow rate (setpoint) is easily field adjustable with included magnet and the unit has both NO and NC NPN outputs.


ServiceCompatible water-based fluids.
Wetted Materials316SS
Pipe Range1/2 to 1-1/2″ (15 to 40 mm) or 2 to 10″ (50 to 250 mm) (model selectable).
Set Point Range0.5 to 10 ft/s (0.15 to 3.0 m/s).
Repeatability0.07 ft/s (0.02 m/s) +3% of setpoint.
Typical Deadband0.1 ft/s (0.03 m/s) +15% of setpoint.
Temperature LimitsAmbient: 5 to 140°F (-15 to 60°C); Process: 5 to 140°F (-15 to 60°C), Storage: -40 to 185°F (-40 to 85°C).
Pressure Limits300 psig (20.67 bar).
Response TimeApprox. 8 s.
Power Requirement9 to 24 VDC.
Switching Current400 mA, de-rate 5 mA/°C above 23°C
Current ConsumptionAverage: 93 mA; Peak: 300 mA.
Electrical Connection1/2′ NPT female or cable gland with 4 conductor 22 AWG 6′ (1.83 m) long (model selectable)
Process Connection1/2″ NPT or BSPT male (model selectable).
Enclosure RatingNEMA 4X (IP65).
Housing Materials316 SS, 416 SS, polycarbonate, neoprene, and acrylated urethane.
Switch Type1 NO NPN, 1 NC NPN.
Input Power and Protection0.5A fuse (resettable) reverse polarity protected.
Switched Output Protection0.5A fuse (resettable) reverse polarity protected.
Agency ApprovalsCE


  • Better reliability and life expectancy than mechanical flow switches with no paddles or vanes to wear or break, no jams in the paddle movement, and no seals on movement assembly to wear or leak
  • Long operation life, as it is not affected by empty pipe by avoiding overheating with heating above the process temperature and then cooling down to process temperature
  • Lower system run cost with low pressure drop with 10% insertion into the flow (e.g. 1/8″ for 3/4″ schedule 40 pipe)