Breaking Down Differential Pressure (DP) Flow Meters Part 2 of 3

Have you read our last blog? Make sure you’re caught up before we take a closer look at why differential pressure (DP) flow meters are an optimal choice, despite their antiquity. First, we must dig deeper to grasp the function of these versatile flow meters.

If they are low-tech, then how do they work?

An In-Dept Exploration of Differential Pressure Flow Meters

Orifice plates, used to measure flow rate, are usually based on concentric discs that are mounted into a pipe. They create a restriction, which generates a pressure drop. Pressure taps are then positioned in accordance with the chosen standard. And since there are so many, the options are quite numerous. 

Usually, pressure taps are one diameter upstream and half-a-pipe diameter downstream to enable reading the line pressure at its lowest point or highest velocity in the vena-contracta. Corner taps are used as well in order to effectively measure the impact pressure and what approaches the vena-contracta pressure. The pressure drop generated is always proportional to the square of the flow. The delta P result must have a square root extraction to give flow rate. Doubling the flow quadruples the pressure drop. This has the disadvantage in which a 100:1 range pressure sensor will only give a 10:1 operating flow range, wherein a typical range for this type of device is normally 4/6:1.

While there have been entire databases written on this subject and the system may require checking to ensure long-term accuracy, the flow must be turbulent. Laminar flow has an entirely different characteristic since the upstream edge of the plate must retain a sharp edge to maintain accuracy. It cannot be used on abrasive or dirty fluids.

Unlike the square law relationship with an orifice plate, a laminar flow element uses low velocity fluid that is not in the turbulent region. This has a large advantage because of the pressure drop across the element is directly proportional to the flow. These devices are extremely useful for small flows that are usually gasses.

The element itself resembles a honeycomb and offers a large surface area and low fluid velocities. These devices are used mostly for low flows because of their operating principle and because larger meters of this kind have high manufacture costs.

As we go further, we will continue with more information in our next blog.  

Aside from explaining differential pressure flow meters, JLC International brings you dew point sensors, carbon dioxide transmitters, dew point monitors and dew point sensors. There is no limit to what we can and will provide for you. We deliver our measurement instruments globally to many different sources all over the world. Contact us today!