# Orifice (diaphragm) calculation

1.
Introduction

2. Pressure drop through an orifice

## 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 diaphragm.

## 2. Pressure drop through an orifice

The following correlation is given by Gibson, it is reproduced in many
books.

**Equation 1 : singularity pressure
drop coefficient for an orifice**

With :

K = Pressure drop coefficient

D = Pipe diameter (m)

d = orifice diameter (m)

u

_{m} = 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**

**Source**

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