Orifice Meter Construction, Working Principle and Derivation

A hole with a sharp edge on a long plate is called an orifice. A plate with this type of hole is called an orifice plate, and now this plate is used to measure the discharge of a liquid. So it is called an orifice meter. 

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Construction

The orifice made in the plate is made concentric with the pipe, in which it is tightened between two flanges, and remains perpendicular to the liquid when it flows. 

The orifice meter is attached to the pipe with the help of a flange, then the connection for the pressure gauge is taken out from both the side pipes of the plates, and the connection of the pressure gauge is made. 

Working Principle

Due to this, there is a decrease in the pressure of the flowing current while coming out of the orifice of the cross-section. This decrease is due to the conversion of the kinetic energy of the get into vertex and eddies and hence the velocity head increases. The decrease in pressure between the nozzles can be determined with the help of a manometer. 

Derivation (Orifice derivation of formula) 

Let the pressure and velocity at points 1 and 2 be P1 and P2 and velocity v1 and v2 respectively. 

Bernoulli's Theorem 

if the orifice meter is connected to the horizontal pipe then z1 =z2 

From the Continuity equation, we get  

A1v1 = A2v2 

Substituting the value of v1 in equation (1) 

If the losses are taken as negligible while deriving the value of v2, the theoretical velocity of v2 will be equal to the velocity of a jet component. 

If Cv = coefficient of velocity then 

Where A1 = Area of sectional tube 

A2 = Area of vena Contra

As the jet comes out of the orifice it is the minimum area A2 if

CE = The Coefficient 

A2 = Ce Aօ 

Aօ  = Area of orifice