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Rotameters for Liquids and Gases.

Pacific Water Technology is an Australian  supplier of high quality  rotameters for liquids and gases including specialised applications like ozone compatible rotameters. Rotameters are the most widely used type of variable-area (VA) flowmeter. In these devices, the falling and rising action of a float in a tapered tube provides a measure of flow rate.


Rotameters provide economical measurement and visual indication of fluid flow

Rotameters are known as gravity-type flowmeters because they are based on the opposition between the downward force of gravity and the upward force of the flowing fluid. When the flow is constant, the float stays in one position that can be related to the volumetric flow rate.  This allows for the measurement of liquids and gases with the scale calibrated to suit the density of the medium.

Pacific Water Technology stocks a wide range of acrylic tube Rotameters used widely in the water treatment industry.  These rotameters are available  with flanged or threaded connections( typically UPVC) in DN or ANSI specifications. Below is an example of an application for a reverse osmosis water treatment plant.

rotameter ro plant

The rotameters can  also be fitted with metallic float to allow for one or two flow switches .This allows for precise monitoring of flow conditions and alarms set at the required levels.

rotameter with flow switch

Pacific Water stock a wide range of rotameters for liquids and gases and we can also supply customised  rotameters to suit your specific needs.  This includes rotameters with guide rods or without , and also customised guide rods for corrosive fluids.  Some factors that need to be taken into consideration when choosing a rotameter:

  • Fluid type. The more information on the nature of the fluid, the better. Is it liquid, gas, or steam? If it is highly corrosive, give its chemical name, e.g., sulphuric acid, and its concentration. Are there entrained solids?
  • Fluid density. Give specific units, such as grams per cubic centimeter, at a specified operating temperature. Alternatively, you can specify fluid-specific gravity, which is the ratio of the fluid density to the density of water (in the case of a liquid) or to that of air (in the case of a gas), at a specified temperature.
  • Fluid viscosity. Again, use specific units such as centipoises or centistokes at a specified operating temperature.
  • Operating and maximum temperature and pressure. This information is very important  for gas applications.
  • Flow rates. What are the minimum and maximum?
  • Required functions. What tasks will your system be expected to do? Will you need to incorporate indicators, control devices, alarms, or remote transmission capabilities?
  • Indicating scale type. Do you want your readout in percent, direct reading, or some other format?
  • Materials of construction. Don’t forget system components such as end fittings, O-rings, regulators, and valves.
  • Valve requirements.  Do you require to control the flow with a needle valve on the flow inlet or outlet?
  • Guide Rod. Do you require a guide rod for the float?

Typical Parameters for the types of Rotameters:

Flow range. Measuring liquid (water) flow rates from 0.65 lpm. to 2000 lpm in pipe from 1/8 to 4 in. dia. and gases (air) from 47 sccm to 24,354 lpm.

Design pressure (typical). Metal tube, to 10 mPag; glass tube, to2068kPag; plastic tube, to 689 kPag.

Design temperature (typical).


Signal. Visual and/or electronic

Accuracy. Typical accuracy ±2% to ±10% F.S., depending on type, size, and calibration

Repeatability.±0.5% to ±1% F.S.

Viscosity. Liquids up to 200 cP


Sizes. Up to 4 in.; also used as a bypass meter around a main line orifice for larger pipe sizes

Rotameters are not suitable for slurries, high viscosity liquids and  reverse  and pulsed flow. For more information on your rotameter requirements, please contact us on

Categories: All, Commercial, Industrial
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