Orifice plate
The most standardized cost-saving solution for a DP flowmeter
Orifice plates or diaphragms are the most commonly used primary elements for differential pressure flow measurement. They allow measurement over a wide range of flow rates and for a wide range of pipe diameters. There are several types:
- the sharp-edge orifice plate, the best known,
- the other concentric plates with conical inlet and quarter circle plate for the measurement of low flows or viscous fluids
- and the eccentric plate or segmental plate for the measuring dirty or impure fluids.
- Finally, the multi-hole / conditioning orifice plate allows a measure of quality while providing a minimum footprint.
The principle of the flow measurement by differential pressure is the following:
The restriction also known as the primary element is fitted within a circular pipe; it creates an obstruction and increases the fluid velocity, which results in a pressure difference between the upstream and downstream sides of the restriction.
This measurement of the differential pressure between the upstream and downstream sides of the restriction is proportional to the flow rate.
The measurement of this pressure difference (called ΔP) is transformed by a differential pressure sensor into a 4-20 mA signal and then translated into a flow rate according to the law:
Q = K √ Δp
Q being the flow
K a constant that takes into account the fluid parameters, the viscosity, the roughness of the pipework, the density of the fluid, etc.
Δp the differential pressure (upstream pressure - downstream pressure).
The differential pressure element shown in this picture is the orifice plate.
There are other types of primary elements more or less adapted to the characteristics of your process. It's about choosing the best solution in terms of measurement quality, size and price.
This table below is a tool to help select the flow measurement primary element.
Depending on the type and characteristics of the fluid to be measured, you will have a first idea of the orifice plate adapted to your application.
Please note, as any first approach, it is imperative to validate the choice by a calculation made by our specialized design office.
For accurate sizing, we need information about your sizing:
You can also log in to SIZEWELL, our online tool for preliminary sizing of primary flow measurement elements. It’s very easy to use and lets you see at a glance (green boxes = OK, red boxes = not OK) which components are suitable for your application.
If you do not find the answer you are looking for, please contact us either by phone at +33 (0)5 59 30 85 20 or via the contact form. We will respond as soon as possible.
The orifice plate (or other flow measurement primary element such as venturi, nozzle ...) creates a restriction in the pipe.
This restriction accelerates the fluid and creates a slight depression.
It is enough to know the upstream (HP high pressure) and downstream pressure value (BP low pressure) of the restriction to be able to calculate the flow that passes through the pipe thanks to the Bernoulli equation. Of course, the orifice plate is standardized and its design and manufacture follow strict criteria so that the measurement is as accurate as possible.
