Variable area flow meter for a wide variety of flows.



  • Tough machined acrylic meter body
  • Direct reading permanent scale
  • Acceptable in direct sunlight applications
  • Reinforced connections with metal thread supports

Variable Area Flowmeters Product Description

The F-400N Series Variable Area Flowmeters have been very popular flowmeters for a long time. These variable area flowmeters feature superior styling, quality materials and a variety of options. F-400N Series variable area flowmeters are machined of the highest quality acrylic which is polished to a crystal clear finish. Additional variable area flowmeter design features include: Corrosion and wear resistant internal parts, sturdy well built adapters and Viton o-ring seals. Permanent scales are screen printed onto the variable area flowmeter body, directly in front of the float for easy reading.

Other variable area flowmeter series, configurations and flow ranges are available. To select a variable area flowmeter other than what we list here we need the desired mounting configuration, liquid being measured, and measurement range in GPM, LPM or SCFM.

Variable Area Flowmeters are tested and calibrated for water or air only. Although variable area flowmeters may be suitable for other chemicals, it is the responsibility of the user to determine the suitability of the variable area flowmeter in their application.

Variable Area Flowmeter Installation Instructions

  1. The variable area flowmeter must be installed in an exact vertical plane to ensure accuracy.
  2. Use Teflon® tape (or similar) on all pipe threads.  Acrylic and other exotic plastics cannot tolerate PVC Glue and/or pipe dope.  Even fumes can cause crazing.  If you are installing your variable area flowmeter to a glued pipe installation, install the variable area flowmeter after all glued fittings are dried and lines are purged of all fumes.  Never hold the variable area flowmeter with pliers or like tools.  DO NOT OVER-TIGHTEN!
  3. Wall, floor and ceiling mounts must be carefully aligned and sturdy.  Wall, floor and ceiling supports are recommended as needed.  This is to maintain pipe alignment and to prevent vibration.
  4. Valves – Avoid a system that will impose a sudden burst of flow to the variable area flowmeter.  Such a burst will cause the float to impact the float stop with destructive force which may damage the variable are flowmeter.  Solenoid valves or other quick opening valves cannot be used unless variable area meter is protected against sudden bursts of flow.  (If necessary a surge chamber should be installed.  This will also be useful in high pressure start-up situations.)  The variable area flowmeter is not warranted against this type of damage.
  5. Maximum working pressure not to exceed recommended psi at fluid temperature (see Variable Area Flowmeter Manual for more information).

Variable Area Flowmeters Specifications

Max. working pressure: 150 PSI (10.3 bar) @ 70 °F (21 °C)
Max. Fluid Temperature
     Polypropylene adapters: 150 °F (65 °C) @ 0 PSI
     PVC adapters and floats: 120 °F (49 °C) @ 0 PSI
Full scale accuracy: +/- 5%
Calibration fluid: water, specific gravity 1.0
Maximum pressure drop: 2 PSI
     F-400N: 8-3/16″ H x 1-1/4″ Dia. (21cm H x 3.2cm dia.)
     F-410N: 11″ H x 1-3/4″ Dia. (28cm H x 4.5cm dia.)
     F-400N: 0.5 lb. (0.23 kg)
     F-410N: 2.0 lb. (0.91 kg)


F-40250LN-4 Variable Area Flowmeter (PN# BWF425)
1/4 inch NPT (F), Flow Range 0.025 to 0.25 gpm (0.1 to 1.0 lpm), PVC connector, PVC float.

F-40050LN-4 Variable Area Flowmeter (PN# BWF450)
1/4 inch NPT (F), Flow Range 0.050 to 0.500 gpm (0.2 to 2.0 lpm), PVC connector, 316 SS float.

F-40375LN-8 Variable Area Flowmeter (PN# BWF401)
1/2 inch NPT (F), Flow Range 0.1 to 1.0 gpm (0.4 to 4.0 lpm), Polypropylene connector, PVC float.

F-40376LN-8 Variable Area Flowmeter (PN# BWF402)
1/2 inch NPT (F), Flow Range 0.2 to 2.0 gpm (1.0 to 7.5 lpm), Polypropylene connector, 316 SS float.

F-40377LN-8 Variable Area Flowmeter (PN# BWF403)
1/2 inch NPT (F), Flow Range 0.3 to 3.0 gpm (1.5 to 11.0 lpm), Polypropylene connector, 316 SS float.

F-40500LN-8 Variable Area Flowmeter (PN# BWF405)
1/2 inch NPT (F), Flow Range 0.5 to 5.0 gpm (2.0 to 20.0 lpm), Polypropylene connector, 316 SS float.


F-40750LN-12 Variable Area Flowmeter (PN# BWF410)
3/4 inch NPT (F), Flow Range 1.0 to 10 gpm (4 to 38 lpm), Polypropylene connector, 316 SS float.

F-41017LN-12 Variable Area Flowmeter (PN# BWF417)
3/4 inch NPT (F), Flow Range 1.0 to 17 gpm (4 to 64 lpm), Polypropylene connector, 316 SS float.

F-41000LN-12 Variable Area Flowmeter (PN# BWF420)
3/4 inch NPT (F), Flow Range 2.0 to 20 gpm (8 to 80 lpm), Polypropylene connector, 316 SS float.

F-41000LN-16 Variable Area Flowmeter (PN# BWF421)
1 inch NPT (F), Flow Range 2.0 to 20 gpm (8 to 80 lpm), Polypropylene connector, 316 SS float.


F-550L Panel Mount Flowmeter

SPX Inline Low Flow Meter
Chemical resistant low flow meters for small diameter pipes