 # Orifice plate (diaphragm) flow and pressure drop calculation

1. Introduction
2. Pressure drop through an orifice
3. Orifice flow and pressure drop calculation tool

## 1. Introduction

Orifices are often used in fluid mechanics to limit mechanically the flow. It is important to be able to size them.

The restriction orifice mentioned here is a thin perforated plate, also called orifice plate or diaphragm.

## 2. Pressure drop through an orifice

How to calculate the pressure drop through an orifice plate ?

The following correlation is given by Gibson, it is reproduced in many books.It relates the flow through the orifice and the pressure drop. Equation 1 : singularity pressure drop coefficient for an orifice

With :
K = Pressure drop coefficient
D = Pipe diameter (m)
d = orifice diameter (m)
um = fluid velocity, before diaphragm, (m/s)
ΔHs = Pressure drop in m

The coefficient K can also be calculated thanks to the following graph :

Graph 1 : K coefficient as a function of d/D ## 3. Orifice flow and pressure drop calculation tool

How to calculate the flow through an orifice plate ?

You can access to an Excel calculation tool in order to assess the flow and pressure drop through an orifice plate : Excel calculation tool

Source

Gibson et al., Hydraulics and its applications, 5th edition, Constable London, 1952