An orifice plate is a device used to measure fluid flow rates by creating a restriction in the pipe. It works by measuring the difference in pressure upstream and downstream of the plate. Fluid must constrict through a precisely measured opening in the plate, causing the pressure to drop and creating a relationship between differential pressure and flow rate. Common applications include measurement of clean liquids and gases. The orifice plate is inexpensive and occupies little space but requires straight pipe sections upstream and downstream for accurate measurement.

1. Orifice plate
aSHVANI Shukla
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2. Orifice Plate
An orifice plate is a device used for measuring flow rate, for
reducing pressure or for restricting flow (in the latter two cases
it is often called a restriction plate). Either a volumetric or
mass flow rate may be determined, depending on the
calculation associated with the orifice plate. With an orifice
plate, the fluid flow is measured through the difference in
pressure from the upstream side to the downstream side of a
partially obstructed pipe. The plate obstructing the flow offers
a precisely measured obstruction that narrows the pipe and
forces the flowing fluid to constrict.

3. continuous
 Orifice Plate is the heart of the Orifice Meter. It
restricts the flow and develops the Differential Pressure
which is proportional to the square of the flow rate. The
flow measuring accuracy entirely depends upon the
quality of Orifice plate, its installation and maintains.
 When measuring wet gas or saturated steam a weep
hole is drilled in a concentrically bored orifice plate.
This is a small hole drilled on the orifice plate such that

4.  The Orifice plates are manufactured as per ISA / AGA/ API / ANSI standards and in
various materials
 such as SS304 /SS316 / SS316L /Hestoly C / Monel / PTFE coated.
 Various bores are used for various applications.
 Orifice Plate is categories in two types :- Paddle Type & Universal Palate.
 Paddle Type Orifice Plate
 This plate is sandwiched between two Orifice Flanges. Tag Plate of orifice plate
projects out from Orifice flanges and it indicates the existence of Orifice plate. Details
such as Tag NO /Orifice ID / Pipe ID / Plate Material are stamped on one side of the tag
plate which faces upstream side of the pipe line. Outside diameter of the orifice plate
equals to PCD-1 Bolt Dia. This ensures the concentricity with the main pipe line. The
other method to maintain the concentricity is by using sleeves on the bolts or by
providing dowel pins on the Orifice Flanges.
 Universal Orifice Plate
 This is a circular plate designed to fit in the Orifice fittings / Plate holders / carrier
rings / Ring Type Joints(RTJ).

5. Technical Specification
1.Size for Integral Design : 15, 20, 25, 40 mm
2.Size for Flanged Design : 25, 40, 50, 65, 80, 100, 150 ...250 mm
3.Material- Flanges & Carrier Ring : A105 / SS304/ SS316 / SS316L / CS & Other
materials on request.
4.Orifice Plate : SS304, SS316, SS316L, Hast C, Monel, PP, PVC,PTFE, Coated or
Clad with PP / HDPE / PTFE.
5.Gasket : CAF / SS Spiral Wound + CAF / PTFE / PVC / Rubber, Other materials
as per special request.
6.Stud / Nut : ASTM A193 Gr B/ASTM A194 CI 2H A193 B16/A194 C14
7.Standards Applicable : Design - ISA RP 3.2 / DN 1952 / BS 1042 - 1981-84
8.Bore Calculation : ISO 5167 / BS 1042 / RW Miller / L. K. SPIN / AGE - 3.7
9.Flanges : ANSI B-16-36 / or Equivalent
10.Types : Square edge concentric, Quadrant edges, Conical entrance,
Eccentric.
11.Pressure Toppings : For 1" to 16" - Flange Taps / Corner Taps. Above 16" - D x
D/2

6. Type Orifice Plate
 Paddle Type Orifice Plate
 Concentric Beveled Bore
Application :
This Most Common Bore Used In The Industries.
This Is The Only Type Generally Accepted For
Use In Custody Transfer Measurement, Since
Adequate Data Is Not Available For Other Bores.
Used Primarily For Clean Homogeneous Liquids,
Gases, Non Viscous Fluids. The Bevel Is Matched
At 45° Angle To The Desired Throat Thickness.

7. Application :
This Type Is Not Used For
Flow Measurement But For
Dropping The Pressure
Considerably And Reducing
The Flow Accordingly. The
Bore Is Not Beveled But Kept
Straight. The Beta Ratio Has
No Limit As Accuracy Is Not
The Goal
Restriction Bore

8. Eccentric Bore
 Application :
Used For Measurement Of Flow
For Fluids Containing Solids And
Slurries. It Is Also Used For
Vapors And Gases Where
Condensation Is Present. The
Eccentric Bore Is Offset To
Where The Bore Edge Is
Inscribed In A Circle That Is 98%
The Line Id.

9. Segmenta Bore
 Application :
 The Segmental Bore Is
Located In The Same Way
That The Eccentric Bore Is.
This Type Is Used Primarily
For Slurries Or Extremely
Dirty Gases Where The
Flow May Contain
Impurities Heavier Than
The Fluid.

10. Quadrant Bore
 Application :
Used For High Viscous Fluids
Such As Heavy Crude,
Syrups And Slurries. It Is
Always Recommended For
Flow Where Reynolds Number
Is Less Than 10,000.The Inlet
Is Quarter Of A Circle And The
Plate Thickness Must Be At
Least Radius Of The Inlet.

11. Ring Type Joint –Integral
 Application :
 These Are
Available In Oval
Or Octal Shapes.
Orifice Plate Is A
Part Of RTJ
Gasket.

12. Ring Type Joint- Separate
 Application :
These Are Available In
Oval Or Octal Shapes.
The Orifice Plate Is
Universal Type And
Snap Fitted On The
RTJ Gasket By
Screws.

13. Universal Orifice Plates
Application :
This Is A Circular Plate Designed To Fit In The
Orifice Fittings / Plate Holders / Carrier Rings /
Ring Type Joints(RTJ).

14. Various Orifice Assemblies
WNRF - Flange Taps WNRF - Corner Taps

15. Orifice working principle
Working:
§The orifice plate, being fixed at a section of the pipe,
creates an obstruction to the flow by providing an opening
in the form of an orifice to the flow passage.
When an orifice plate is placed in a pipe carrying the fluid
whose rate of flow is to be measured, the orifice plate
causes a pressure drop which varies with the flow rate.
This pressure drop is measured using a differential
pressure sensor and when calibrated this pressure drop
becomes a measure flow rate. The flow rate is given by.

16. Where, Qa = flow rate
Cd = Discharge coefficient
A1 = Cross sectional area of pipe
A2 = Cross sectional area of orifice
P1, P2 = Static Pressures
•The main parts of an orifice flow meter are as follows:
A stainless steel orifice plate which is held between flanges of a pipe carrying the fluid
whose flow rate is being measured.
•It should be noted that for a certain distance before and after the orifice plate fitted
between the flanges, the pipe carrying the fliud should be straight in order to maintain
laminar flow conditions.
•Openings are provided at two places 1 and 2 for attaching a differential pressure sensor
(U-tube manometer, differential pressure gauge etc) as shown in the diagram.

17. Operation of Orifice Meter

The detail of the fluid movement inside the pipe and orifice plate has to be understood.
 The fluid having uniform cross section of flow converges into the orifice plate’s opening in its
upstream. When the fluid comes out of the orifice plate’s opening, its cross section is
minimum and uniform for a particular distance and then the cross section of the fluid starts
diverging in the down stream.
 At the upstream of the orifice, before the converging of the fluid takes place, the pressure
of he fluid (P1) is maximum. As the fluid starts converging, to enter the orifice opening its
pressure drops. When the fluid comes out of the orifice opening, its pressure is minimum
(p2) and this minimum pressure remains constant in the minimum cross section area of fluid
flow at the downstream.
 This minimum cross sectional area of the fluid obtained at downstream from the orifice edge
is called VENA-CONTRACTA.
 The differential pressure sensor attached between points 1 and 2 records the pressure
difference (P1 – P2) between these two points which becomes an indication of the flow rate
of the fluid through the pipe when calibrated.

18.  Applications of Orifice Meter

The concentric orifice plate is used to measure flow rates of pure fluids and has a wide applicability as it has
been standardized.
 The eccentric and segmental orifice plates are used to measure flow rates of fluids containing suspended
materials such as solids, oil mixed with water and wet steam.

Advantages of Orifice Meter

It is very cheap and easy method to measure flow rate.
 It has predictable characteristics and occupies less space.
 Can be use to measure flow rates in large pipes.

Limitations of Orifice Meter

The vena-contracta length depends on the roughness of the inner wall of the pipe and sharpness of the
orifice plate. In certain cases it becomes difficult to tap the minimum pressure (P2) due to the above factor.
 Pressure recovery at downstream is poor, that is, overall loss varies from 40% to 90% of the differential
pressure.
 In the upstream straightening vanes are a must to obtain laminar flow conditions.
 Gets clogged when the suspended fluids flow.
 The orifice plate gets corroded and due to this after sometime, inaccuracy occurs. Moreover the orifice plate
has low physical strength.
 The coefficient of discharge is low.