Liquid Mass Flow Meter – Selecting The Right Flow Meter.

This article will cover the various types of liquid mass flow meters available. They are generally defined by the way they work. Each has it's own advantages and disadvantages. All these issues will be covered so that you have a better idea of the type of liquid mass flow meter you may need.

Paddle-Wheel Flow Meter

As the name suggests, this type of liquid mass flow meter uses paddles that have magnets attached to the ends of each paddle. The paddles are turned by the water or liquid passing them. The magnets send a reading about the mass flow which is picked up by a sensor.

This type of flow meter will need to be installed in a section of pipe that has no bends.  There are also minimum pipe requirements both upstream and downstream. So it is important that you know the type of pipe that you will be using, especially the pipe length where you would like to place the paddle-wheel liquid mass flow meter.

This type of meter will avoid common issues of pressure drop and is easy to maintain.  This is also a good option if you are looking for a reliable meter that has good repeatability. If the liquid you are trying to measure is of a foamy consistency or turbulent in anyway you will want to avoid this type of liquid mass flow meter.  The sensors in the gauge will not be able to provide you with an accurate read. 

Turbine Flow Meter

This liquid mass flow meter works by using a complex system of impeller blades, and either magnets or infrared beams to create an electric pulse that will eventually be converted into your reading.  Best used with a low-viscosity liquid that offers little resistance in its flow.

Like the paddle-wheel flow meter this version requires a straight distance of pipe before the turbine liquid mass flow meter.  You will need to check the specific device for requirements before installing.

While this type of flow meter does work best with liquids, specific models can be used with gas.  If you are trying to measure thermal properties you will need to purchase a thermal mass flowmeter. 

Rotameter

The Rotameter is a popular and relatively inexpensive liquid mass flow meter. The principle behind it is that it diverts some of the liquid through a gauged tube or piping. Within the tube is a float that is pushed by the force of the liquid passing through. Where the float stops along the gauge is an indication of the mass flow of the particular liquid.

The main drawback of these types of flow meters is that the reading is taken by eye. So some human error can occur in the reading and the gauge has to be in an accessible location so that it is easy to read.
 
By switching out the type of float used inside of the gauge you can measure different types of flow rates.  Rotameters are also available in several different types of materials to allow use with different types of chemicals and gases.