AS-FS Flow Switch for Air or Liquids

FCI's AS-FS Series flow switches utilize no moving parts, ultra-reliable thermal dispersion flow measurement technology to detect a flow rate above or below a predetermined set point at the sensing location.  They are applied to signal low flow or high flow alarm conditions in air or liquid fluid flows throughout the aircraft.  FCI offers two versions, one for air flow and one for liquid flow applications.. They are rugged, all-welded, 316 stainless steel but are compact and lightweight.  AS-FS flow switches are directly installed into piping or ducting on commercial and military aircraft, as well as spacecraft, vehicles and marine applications.

Please contact us or use the "request a quote" button above to obtain technical quotation for your Flow Switch application.


  • Liquid Cooling Systems
  • Fuel Transfer
  • Cooling Fan Failure Alarm
  • Fuel Tank Inerting Systems
  • Lubricating Oils
  • Air Management Systems
  • PACK Air Systems
  • Hydraulic Fluids
  • Bleed Air Systems
  • Ground and In-Flight Refueling
  • Environmental Cooling Systems
  • RAM Air Flow Failure Alarm


Service: Flow monitoring of liquids, air or gases.

Material: Wetted parts 316 stainless steel, all welded construction

Electronics Enclosure: Hermetically sealed units; 316 stainless steel

Electrical Connection: D38999 or compatible

Process Connection: Flanged with O-ring seal

Insertion Length: Per customer requirement

Output Options
  • Flow Signal: Source 240 mA at 28 Vdc
  • No Flow Signal: Source 0 Vdc
  • Flow Signal: Source 0 Vdc
  • No Flow Signal: Source 240 mA at 28 Vdc

Open Collector
  • Flow Signal: Closed, sinking up to 100 mA at < 0.5 Vdc
  • No Flow Signal: Open, leakage < 10µa at 30 Vdc
  • Flow Signal: Open, leakage < 10µa at 30 Vdc
  • No Flow Signal: Closed, sinking up to 100 mA at < 0.5 Vdc

Electrical Power Input: 28 VDC nominal per MIL-STD-704

Power Consumption: 3 watt maximum

Weight: 8 oz. [227 g] maximum

Operating Pressure: Standard up to 2000 psig [138 bar (g)]; higher pressures available by request, contact FCI

Switch Point Adjustment
Factory set at customer specified switch point within flow range listed:
   Air:          0.25 to 1000 SFPS [0.07 to 305 MPS]
   Liquids:  0.01 to 10 SFPS [0.003 to 3 MPS]
Operating Temperature Range
  Flow Element: - 65 °F to 350 °F [- 54 °C to 175 °C] Specify actual requirement
  Electronics: - 40 °F to 257 °F [- 40°C to 125 °C]

Repeatability: ± 2% of full signal range

Time Response: 5 to 15 seconds typical, depending on fluid type and switch point

EMI and Lightning Protection: MIL-STD-461 and RTCA/DO-160

Qualifications: MIL-STD-810 and RTCA/DO-160

Quality Systems Approval: ISO 9001, AS9100