The intention of this general description is only to update the basic knowledge of your technical studies, it can also be an introduction to the topic, but the reader must have a basic knowledge about fluid dynamics to better understand the presented information. Flow rate measurement based on differential pressure drop can now be considered a reliable and well-proven measure. The first notices of the use of this technology go back to the Egyptian era, although the orifice plates with more resemblance to the current plates have been used for the last 120 years.
During the professional life of a person related to the world of industrial instrumentation, many times an instrumentation technician or an instrumentation engineer needs to make the calculation of a specific orifice plate sizing. An orifice plate is a very powerfull and cheap flow measurement device. It has a minimal operation cost.
Sometimes it is a new installation, in this case we will have all the design information, and other times it is a maintenance or verification intervention that requires to check or calculate the gas flow through an orifice plate.
In this article we present a free online orifice plate sizing calculator that allows us to calculate the size of the hole needed to perform the measurement of a given mass flow rate based on the pressure difference.
1.1 What is an Orifice Meter?
An orifice plate is essentially a plate with a hole machined through it. This plate is inserted in the pipe where we want to perform the flow rate measurement. It can be used for gases, liquids and vapors.
As the flow passes through the hole it generates a pressure drop difference through the hole (part of which is recovered). The pressure drop difference is proportional to the square of the flow (mass or volume).
The basic theory is that if a fluid flowing through a restriction or orifice will suffer a pressure drop proportional to the flow rate. Therefore, it is possible to determine the pressure difference with the flow velocity.
This orifice plate sizing calculator online allows us to calculate the necessary diameter to perform this type of measurements based on dP, it is applicable to gases, liquids and vapors with a defined percentage in water.
The required information is divided into 2 groups, fluid information and instrument information.
Regarding the fluid, basic data are requested from the point of operation (or point of application), as well as some constant depending on the type of gas used.
For the instrument, information is requested on the pipe where it is installed, as well as the range of the pressure transmitter with which we want to measure the flow. The value “Indication X of qm on scale” allows to make a scaling of the final value limiting the maximum range of the instrument.
2.1 Orifice Plate Beta Ratio
The orifice plate beta ratio is a numerical value who relates Orifice Diameter and the internal Pipe Diameter.
Beta Ratio = Orifice diameter / internal Pipe diameter
The orifice plate has a typical bore diameter that goes from 30% to 75% of the internal diameter of the installed pipe.
An orifice plate beta ratio of 0.6 means that the orifice plate bore diameter is 60% of the pipe internal diameter.
3. Basic Rules
- In red you will find an orifice calculation, feel free to substitute this numbers with your own ones. By default, the calculator will show an orifice plate calculation example.
- Use a dot to represent a decimal point e.g. 4353.56
- In case you need to convert from/to Normal or Standard flow rate use the links above.
- All the cells that have a red asterisk are considered necessary information to perform the calculation.
4. Other Tools
This calculator can be used for orifice plate bore size calculations for given values of the flow rate and measured pressure drop in front and after the orifice. If you need to calculate from standard or normal flows to mass flow rate you can use the following conversion tools:
- ARIAN Control & Instrumentation – Technical note 12, Differential pressure mass flow meter.