Orifice plate calculator pressure drop calculation online. This orifice plate pressure drop and flow calculation requires Java.

Pressure drop is often defined as the difference in pressure between two points of a fluid in a conduit. Pressure drop occurs with frictional forces, caused by the resistance to flow on a fluid as it flows through the tube or pipe. The main factors of resistance to fluid flow are fluid viscosity and fluid velocity. Pressure drop increases proportional to the frictional shear within the pipe. High flow velocities and or high fluid viscosities result in a larger pressure drop across a section of pipe or a valve or elbow. Low velocity will result in lower or no pressure drop. This particular pressure drop calculator deals with what happens with orifice plates. This site also has other calculator dealing with venturi and pitot tube calculations on other pages.

Orifice plate pressure drop calculator is used for flow rate measuring in pipe systems. With orifice plate, pressure drop is created. Based on the magnitude of pressure drop, flow rate can be calculated. The pressure drop calculation formula for the pipe is explained in more detail below .Practical for larger tube diameters and for dirty fluid where other methods are impractical.

Measure pressure drop from position 1 to position 2 and calculate flow rate and more with this easy to use flow calculator .Pressure drop formula calculation is published. It can be used as liquid, gas or air flow meter and the results can be checked against the textbook formula to gain confidence in using this easy to use orifice plate pressure drop /flow rate calculation . Flow rate can be expressed in metric or imperial units.

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Explanation of used values
p1 - p2
diameter of tube
throat diameter
upstream pressure
downstream pressure
pressure drop through orifice
kinematic viscosity
dynamic viscosity
upstream temperature
upstream density
gas constant
isentropic coefficient


Resulting values
volumetric flow rate
mass flow rate
upstream velocity
throat velocity
upstream Reynolds number
expansion coefficient
coefficient of discharge


Calculation of flow rate using orifice plate calculator is for incompressible flow, based on the Bernoulli principle:

where is:
p - pressure
rho - density
V - velocity
g - gravitational constant (9.81 m/s2)
z - geodetic height

Assumption that pressure lost is negligible (pressure drop is obvious and included with coefficient of discharge which is introduced bellow):


and if velocities substituted with flow rate:

where is: Q - volumetric flow rate
D - diametar

Pressure drop through the orifice because of velocity increase can be calculated as follows:


Expressing flow rate from the previous equation leads to:


flow rate can be determined as:

where is:
C - coefficient of discharge
e - expansion coefficient

Coefficient of discharge can be calculated using following equation (ISO):

where is:
beta - diameter relation D2/D1
ReD - Reynolds number which can be calculated as follows:

where is:
ni - kinematic viscosity
mi - dynamic viscosity

L1 and L2 are functions on tap type and it is:
L1=L2=0 for corner taps
L1=1 L2=0.47 for D & D/2 taps
L1=L2=0.0254/D D[m] for 1" taps

Expansion coefficient e can be calculated (for gases only):

where is:
kappa - isentropic coefficient; kappa = 1.4 for air and other two atom gas molecules

Other values are calculated using following equations:

mass flow:


If flowing fluid is gas, then it is considered as incompressible and ideal. Equation for ideal gas:

can be used for calculation of temperature T:

as well as density rho:

where R is gas constant (R=287 J/kgK for air).


Orifice plate calculator can be used for both liquids and gases. Fluid is considered as incompressible, so density (rho) and temperature (T) are constant through tube. Also, gas is considered as ideal.
Units of measure are both in SI and English system.

Orifice plate calculator can be used for calculation of:

volumetric flow - Q
mass flow - G
velocity on inlet, bigger diameter - V1
velocity on smaller diameter - V2
Reynolds number on bigger diameter - ReD

For calculation of those values, necessary values for input are:

inlet, bigger diameter - D1
smaller diameter - D2
inlet pressure - p1
either pressure on smaller diameter - p2, or pressure drop p1-p2
either kinematic viscosity - ni, or dynamic viscosity - mi
for gases only:
either temperature - T, or density - rho
gas constant - R
for liquids:
density - rho

Beside four values (Q, G, V1, V2), which calculation is main purpose of calculator, values that are not defined by user are determined in process of calculation (for example: if pressure p1 and temperature T are specified for gas flow - value for rho is calculated together with four main values (Q, G, V1, V2)). Also necessery coeffients: expansion - e and discharge - C are calculated and results are shown