Flow Meter

What is a Flow Meter?

A flow meter is a device used to measure the flow rate or quantity of a gas or liquid moving through a pipe. Flow measurement applications are very diverse and each situation has its own constraints and engineering requirements. Flow meters are referred to by many names, such as flow gauge, flow indicator, liquid meter, etc. depending on the particular industry; however the function, to measure flow, remains the same.

Why do I need a precision flow meter? You might not! Precision flow meters are used to provide accurate monitoring and/or flow control. Some industrial applications require precise calculation of quantity, such as precision servo-valve development for the aerospace industry. On the other hand, an application to measure water flow to a vineyard may only require a measurement accuracy of 5% to 10%.

What are the various types of flow meters?

Positive Displacement (Also known as a Volumetric flow meter or PD flow meter). 
All Max Machinery flow meters are Positive Displacement/Volumetric.
Positive displacement flow meters are unique as they are the only meter to directly measure the actual volume. All other types infer the flow rate by making some other type of measurement and equating it to the flow rate. With PD meters, the output signal is directly related to the volume passing through the meter. Includes bi-rotor types (gear, oval gear, helical gear), nutating disc, reciprocating piston, and oscillating or rotary piston.

Mass
The output signal is directly related to the mass passing through the meter.
Thermal and Coriolis flow meters fall into this category.

Velocity 
The output signal is directly related to the velocity passing through the meter.

• Electromagnetic
• Ultrasonic
• Turbine, Propeller, and Paddle Wheel or Pelton Wheel
• Vortex Shedding and Sonar
• Target and Vane
• Variable Area and Rotameter
• Orifice Plate, Open Channel, Flow Nozzle, Laminar, Venturi, and Pitot Tube

What type of flow meter is best? There are no “universal” flow meters which are suitable for all applications. Selecting the proper technology for your application requires writing a flow specification which covers the use of the meter. There are usually trade-offs with each meter type, so knowing the critical specifications will be important. Things you must know:

• What Gas or Liquid will be measured?
• Minimum and maximum flow rates.
• What are the accuracy requirements?
• The fluid temperature and viscosity.
• Fluid compatibility with the materials of construction (See our materials compatibility guide)
• The maximum pressure at the location.
• What pressure drop is allowable?
• Will the meter be mounted in a hazardous location where explosive gases may be present?
• Is the fluid flow continuous or intermittent?
• What type of output signal or readout do you need?

You will use this list to eliminate the technologies that do not apply (ex. Turbines don’t work for viscous fluids, Coriolis meters don’t respond fast enough for injection flow). Then you will have an apples-to-apples comparison of the remaining technologies. Accurate meters are priced based on their capabilities. It is better to locate the type of meter which fits your application before trading features for cost savings. Closely evaluate your extreme conditions, such as low flow rates, high pressure or temperature or the need to measure over a wide operating range. If these conditions are important, do not be swayed by lower priced alternatives that would be applied outside of their capabilities.