NVA Low Flow Glass Tube Variable Area Flowmeter
The NVA GIass tube Variable Area Flowmeter is
available in a full range of lengths and is available
scaled for liquid or gas measurement. Customised
scales match the meter to specific conditions.
There is a choice of three scale lengths for optimum
readability or compact installation. Repeatability is
better than 0.5% of reading to improve process
control. An optional needle valve is available for
precise control at reduced cost. The tubes are
removable from the frame for easy cleaning/
replacement. Angled or straight connections allow
for flexible pipe layout. The meters can be simply
mounted to reduce installation costs. The instruments
have a retained polycarbonate cover to ensure
operator safety in the event of a breakage.
The units are aesthetically styled to suit integration
into original equipment.
Operating principle
Fluid flowing vertically through a tapered tube exerts
an upward force on the float such that the float takes
up a point of equilibrium where the downward
weight is balanced by the upward thrust of the fluid.
This point then represents a specific flowrate. Increase
in fluid velocity will cause the float to rise again until
the next equilibrium point is reached, and this
represents a higher specific flowrate. The tube may
thus be scaled in terms of flowrate in an almost
linear manner.
Ranging and scaling depends on three main factors –
- Shape and density of the float
- Taper of the tube
- Fluid density and viscosity
Several special versions of the NFX flowmeter are
available. The long series provide maximum
readability and extended flow ranges, suitable for
laboratory and calibration applications. Accuracy of
1% of reading to fully traceable standards is available
on request. An infrared alarm can be fitted which can
be user Set to provide a switched output on safety
critical applications. Units can be fitted with a bench
stand for laboratory applications. Anaesthetic flow
tubes for use in medical equipment are available for
air, oxygen and nitrous oxide.
| Technical Data | |
| Flow Ranges | Gas range 20cc/min – 115 l/min (air equivalent). Liquid ranges 2.0 cc/min – 4.6 l/min (water equivalent) |
| Scale length options | 140mm / 100mm / 30 mm |
| Accuracy class -% | 1.6 / 2.5 / 4 VDI/VDE |
| Temperature range | -15°C to +20°C |
| Maxumun pressure | 20 Bar Non shock |
| Connections | Stainless Steel or Nickel plated brass. 1/4” BSP Female |
| Seals | Viton |
| Flow Tube | Borosilicate glass |
| Float | Stainless Steel, Anodised Aluminium |
|
 |
| Compact Glass Tubes: For 1/4” Flowmeter | |||||
| Units | Air | Float Material | Tube Size | Floats are St. Steel | Water H2O |
| cc/min | 20-200 | Dural | 5 | cc/min | – |
| 50-500 | Dural | 15-80 | |||
| L/min | 0.2-1 | Dural | – | ||
| 0.5-2.5 | Dural | 9 | 25-250 | ||
| 0.5-5 | Dural | 100-700 | |||
| 2-12 | Dural | L/min | 0.2-1 | ||
| 5-25 | St. Steel | – | |||
| Standard Glass Tubes for 1/4” or 1/2” Flowmeters | ||||||||||||||||
| Units | Air | Argon Ar | Butane C4H10 | Carbon Dioxide CO2 | Carbon Monoxide CO | Cracked Ammonia N:3H | Helium He | Hydrogen H2 | Methane CH4 | Nitrogen N2 | Oxygen O2 | Propane C3H8 | Float Material | Tube Size | Floats are St.Steel | Water H2O |
| cc/min | 5-100 | 5-80 | 20-130 | 10-100 | 10-100 | 10-120 | 5-100 | 20-250 | 10-150 | 5-100 | 5-90 | 10-140 | Dural | 5 | cc/min | – |
| 20-250 | 20-200 | 50-290 | 20-250 | 20-270 | 30-360 | 2-280 | 40-600 | 40-360 | 20-250 | 20-220 | 40-300 | Dural | 1-10 | |||
| 60-600 | 60-560 | 100-700 | 60-600 | 50-700 | – | 50-800 | – | 0.05-0.9 | 60-600 | 40-600 | 100-700 | Dural | 2-25 | |||
| 50-750 | 40-660 | 100-800 | 50-750 | 50-800 | – | 0.05-1.1 | 0.1-2 | 0.1-1.1 | 50-800 | 50-700 | 100-850 | Dural | 4-60 | |||
| L/min | 0.1-1.2 | 0.1-1 | 0.1-1.1 | 0.1-1.1 | 0.1-1.2 | 0.1-1.8 | 0.1-1.8 | 0.2-3.4 | 0.1-1.7 | 0.1-1.2 | 0.1-1.1 | 0.1-1.2 | St. Steel | – | ||
| 0.2-2 | 0.2-1.7 | 0.4-2 | 0.2-1.8 | 0.2-2 | 0.3-3 | 0.2-3 | 0.4-5.6 | 0.4-2.8 | 0.2-2 | 0.2-1.8 | 0.3-2.2 | Dural | 9 | – | ||
| 0.3-3.4 | 0.2-2.9 | 0.5-3 | 0.3-3 | 0.3-3.5 | 0.4-5.8 | 0.3-5.8 | 0.5-10 | 0.4-4.8 | 0.3-3.5 | 0.3-3.2 | 0.3-3.4 | PEEK | 30-280 | |||
| 0.6-5 | 0.4-4 | 0.8-4 | 0.6-4.4 | 0.6-5 | 1-8 | 0.5-9 | 1-15 | 0.6-5 | 0.4-4.4 | 0.8-4.8 | Dural | 40-480 | ||||
| 1-10 | 1-8 | 1.5-8 | 1-8.5 | 1-10 | 2-18 | 2-20 | 3-34 | 1-10 | 1-9.5 | 1.5-9 | St. Steel | 50-750 | ||||
| 1-13 | 1-11 | 1-10 | 1-11 | 1-12 | 2-22 | 1-28 | 2-46 | 1-13 | 1-12 | 1-11 | Dural | – | ||||
| 2-26 | 2-22 | 2-19 | 2-20 | 2-26 | 4-48 | 2-60 | 5-95 | 2-27 | 2-25 | 2-22 | St. Steel | L/min | 0.1-1.2 | |||
| 4-50 | 4-44 | 4-36 | 4-40 | 6-54 | 10-90 | 5-120 | 10-180 | 4-50 | 4-50 | 4-40 | Dural | 15 | 0.3-3 | |||
| 10-100 | 10-90 | 10-70 | 10-80 | 10-100 | 20-180 | 20-270 | 40-400 | 10-100 | 10-100 | 10-85 | St. Steel | 0.4-4.4 | ||||
| Long Glass Tubes: For 1/4” Flowmeter | |||||
| Units | Air | Float Material | Tube Size | Floats are St. Steel | Water H2O |
| L/min | 0.05-1.6 | St. Steel | 5 | cc/min | 2-80 |
| 0.3-4.6 | PEEK | 9 | 30-380 | ||
| 0.5-16 | Dural | – | |||
| 1-33 | St. Steel | L/min | 0.05-1.5 | ||
| 5-115 | St. Steel | 15 | 0.1-3.4 | ||
| – | – | 0.1-4.8 | |||
| – | – | – | |||
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