Velocity Meters or Displacement Meters?

Which one to Choose?

Having to choose between velocity meters or displacement meters is a decision that many water meter buyers face. The decision will depend on the flow rate required and the purpose of the water meter. Let’s take a look at how they operate and then the advantages of choosing one.

Whereas a water velocity meter measures the velocity of flows, displacement meters use either oscillating piston meters or nutating disks to calculate flow rates.

Both displacement meters and velocity meters are accurate at low flow rates; however, because of their measuring elements displacement meters are able to measure extremely low flow rates.

You will find that most Displacements meters cost slightly more than velocity meters in meter sizes ranging from 1/2” to 2”.

On the other hand, velocity meters are more accurate at higher flow rates than displacement meters. This is because displacement meters depend on all the water passing through the meter to move the pistons or the nutating disks and velocity meters don’t.

Let us now take at look at the advantages of each flow measurement over the other when choosing between velocity meters or displacement meters.

Advantages of Velocity Meters over Displacement Meters

  1. They typically cost less than displacement meters. That is, if you are searching for a ½” velocity or displacement meter, generally the displacement meter will cost more.
  2. You have a wider selection of velocity meters than displacement meters. Velocity meters include Single-Jet, Multi-Jet, Turbine, compound, Propeller, and Ultrasonic.
  3. More accurate at high flow rates than displacement meters.

Advantages of Displacement Meters over Velocity Meters

  1. Exceedingly accurate at low flow rates. The nutating disks or oscillating pistons makes this possible.
  2. They can be installed vertically and will still measure precisely unlike velocity meters. It is recommended that for correct readings, velocity meters should be installed horizontally only.