Variable area flow meters are among the oldest and most mature principles in flow measurement. Based upon Bernoulli's theorem, these meters consist of a uniformly tapered
flow tube, a float, and a measurement scale. As a gas or liquid is introduced into the tube the float rises, its weight supported by the fluid flowing underneath, until the entire volume of
fluid can flow past the float. The position of the float corresponds to a point on the tube's measurement scale and provides an indication of the fluid's flow rate.
The operating principle of variable area meters is as simple as it is reliable. They are generally inexpensive, easy to install and feature low, nearly constant, pressure drop. However, concern
for orientation of rotameters (floats) must be observed, as they must be mounted vertically and have moderate accuracy. Variable area flow meters are generally not suitable for low-flow applications.
Selecting a Flow Meter
The basis of good flow meter selection is a clear understanding of the requirements of the particular application. Therefore, time should be invested in fully evaluating the nature of the process
fluid and of the overall installation.
- What is the fluid being measured by the flow meter(s) (air, water, etc…)?
- Do you require rate measurement and/or totalization from the flow meter?
- If the liquid is not water, what viscosity is the liquid?
- Is the fluid clean?
- Do you require a local display on the flow meter or do you need an electronic signal output?
- What is the minimum and maximum flow rate for the flow meter?
- What is the minimum and maximum process pressure?
- What is the minimum and maximum process temperature?
- Is the fluid chemically compatible with the flow meter wetted parts?
- If this is a process application, what is the size of the pipe?
If you have any questions or need any help selecting a flow meter, please contact us at sales@instrumart.com or 1-800-884-4967 to speak with an applications engineer.
