This video (courtesy of Ashcroft) does an outstanding job illustrating the concepts of differential pressure and flow measurement using the differential pressure method.
Engineered restriction devices are often inserted into a closed pipe system to create a differential pressure for the purposes of measuring fluid flow rate. These restrictions can come in the form of an orifice plates, Venturi, wedge, and other designs.
To measure the differential pressure, taps must be installed on both sides of the plate. The upstream side will always produce the greater pressure, and is referred to as the high side. Conversely, the downstream pressure will always be the lesser value, due to the obstruction.
A differential pressure gauge's range is based on the maximum difference that can be expected as a result of the restriction. The gauge's dial will display the differential pressure in units of pressure measurement, like psi or bar. By applying the linear square root relationship between flow rate and pressure, the gauge style can be scaled in a specified rate of flow, such as gallons per minute. A dual scale dial can also be created to display both the flow rate and the differential pressure.
Another important consideration is the maximum line pressure, also referred to as the static pressure. The higher the static pressure, the more robust the gauge must be to contain it. That's why it's crucial to ensure that the gauge carries a static pressure rating that exceeds the highest pressure in the line.
For more information about differential pressure gauges, transmitters, and flow measurement, contact Mead O'Brien at (800) 892-2769 or visit their web site at https://meadobrien.com.
