Inst ToolsInst ToolsInst Tools
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Search
  • Books
  • Software
  • Projects
  • Process
  • Tools
  • Basics
  • Formula
  • Power Plant
  • Root Cause Analysis
  • Electrical Basics
  • Animation
  • Standards
  • 4-20 mA Course
  • Siemens PLC Course
Reading: Basics of Orifice Plates
Share
Font ResizerAa
Inst ToolsInst Tools
Font ResizerAa
  • Courses
  • Design
  • PLC
  • Interview
  • Control System
Search
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Inst Tools > Blog > Flow Measurement > Basics of Orifice Plates

Basics of Orifice Plates

Orifice plates are typically sandwiched between two flanges of a pipe joint, allowing for easy installation for fluid to flow through the pipe.

Last updated: November 1, 2023 4:21 pm
Editorial Staff
Flow Measurement
No Comments
Share
8 Min Read
SHARE

Of all the pressure-based flow elements in existence, the most common is the orifice plate. This is simply a metal plate with a hole in the middle for fluid to flow through.

Contents
Orifice PlatesConcentric Orifice PlateSquare-edged Orifice Platessquare-edged orifice platesEccentric Orifice Platesegmental orifice plateOrifice Plate with Vent and Drain HolesQuadrant-edge orifice platesConical-entrance orifice plate

Orifice plates are typically sandwiched between two flanges of a pipe joint, allowing for easy installation and removal:

Orifice Plates

Orifice plates

The point where the fluid flow profile constricts to a minimum cross-sectional area after flowing through the orifice is called the vena-contracta, and it is the area of minimum fluid pressure.

The vena-contracta corresponds to the narrow throat of a venturi tube. The precise location of the vena-contracta for an orifice plate installation will vary with flow rate, and also with the beta ratio (β) of the orifice plate, defined as the ratio of bore diameter (d) to inside pipe diameter (D):

Orifice beta ratio

Concentric Orifice Plate

The simplest design of orifice plate is the square-edged, concentric orifice. This type of orifice plate is manufactured by machining a precise, straight hole in the middle of a thin metal plate.

Looking at a side view of a square-edged concentric orifice plate reveals sharp edges (90o corners) at the hole:

concentric orifice plate

Square-edged Orifice Plates

Square-edged orifice plates may be installed in either direction, since the orifice plate “appears” exactly the same from either direction of fluid approach.

In fact, this allows square-edged orifice plates to be used for measuring bidirectional flow rates (where the fluid flow direction reverses itself from time to time).

A text label printed on the “paddle” of any orifice plate customarily identifies the upstream side of that plate, but in the case of the square-edged orifice plate it does not matter.

For example : Here in below image, Label is : INLET

Orifice Plate Parts
Image Courtesy: Emerson

The purpose of having a square edge on the hole in an orifice plate is to minimize contact with the fast-moving moving fluid stream going through the hole. Ideally, this edge will be knife-sharp.

If the orifice plate is relatively thick (1/8 or an inch or more), it may be necessary to bevel the downstream side of the hole to further minimize contact with the fluid stream:

Square-edged orifice plate

Looking at the side-view of this orifice plate, the intended direction of flow is left-to-right, with the sharp edge facing the incoming fluid stream and the bevel providing a non-contact outlet for the fluid. Beveled orifice plates are obviously uni-directional, and must be installed with the paddle text facing upstream.

square-edged orifice plates

Other square-edged orifice plates exist to address conditions where gas bubbles or solid particles may be present in liquid flows, or where liquid droplets or solid particles may be present in gas flows.

Eccentric Orifice Plate

The first of this type is called the eccentric orifice plate, where the hole is located off-center to allow the undesired portions of the fluid to pass through the orifice rather than build up on the upstream face:

eccentric orifice plate

For gas flows, the hole should be offset downward, so any liquid droplets or solid particles may easily pass through. For liquid flows, the hole should be offset upward to allow gas bubbles to pass through and offset downward to allow heavy solids to pass through.

segmental orifice plate

The second off-center orifice plate type is called the segmental orifice plate, where the hole is not circular but rather just a segment of a concentric circle:

Square-edged segmental orifice plate

As with the eccentric orifice plate design, the segmental hole should be offset downward in gas flow applications and either upward or downward in liquid flow applications depending on the type of undesired material(s) in the flowstream.

Orifice Plate with Vent and Drain Holes

An alternative to offsetting or re-shaping the bore hole of an orifice plate is to simply drill a small hole near the edge of the plate, flush with the inside diameter of the pipe, allowing undesired substances to pass through the plate rather than collect on the upstream side.

If such a hole is oriented upward to pass vapor bubbles, it is called a vent hole. If the hole is oriented downward to pass liquid droplets or solids, it is called a drain hole. Vent and drain holes are useful when the concentration of these undesirable substances is not significant enough to warrant either an eccentric or segmental orifice:

Orifice plate with vent and drain holes

The addition of a vent or drain hole should have negligible impact on the performance of an orifice plate due to its small size relative to the main bore. If the quantity of undesirable material in the flowstream (bubbles, droplets, or solids) is excessive, an eccentric or segmental orifice plate might be a better choice.

Some orifice plates employ non-square-edged holes for the purpose of improving performance at low Reynolds number values, where the effects of fluid viscosity are more apparent. These orifice plate types employ rounded- or conical-entrance holes in an effort to minimize the effects of fluid viscosity.

Experiments have shown that decreased Reynolds number causes the flowstream to not contract as much when traveling through an orifice, thus limiting fluid acceleration and decreasing the amount of differential pressure produced by the orifice plate.

However, experiments have also shown that decreased Reynolds number in a venturi-type flow element causes an increase in differential pressure due to the effects of friction against the entrance cone walls.

By manufacturing an orifice plate in such a way that the hole exhibits “venturi-like” properties (i.e. a dull edge where the fast-moving fluid stream has more contact with the plate), these two effects tend to cancel each other, resulting in an orifice plate that maintains consistent accuracy at lower flow rates and/or higher viscosities than the simple square-edged orifice.

Quadrant-edge orifice plates

Two common non-square-edge orifice plate designs are the quadrant-edge and conical-entrance orifices. The quadrant-edge is shown first:

Quadrant-edge orifice plates

Conical-entrance orifice plate

The conical-entrance orifice plate looks like a beveled square-edge orifice plate installed backwards, with flow entering the conical side and exiting the square-edged side:

Conical-entrance orifice plate

Here, is it vitally important to pay attention to the paddle’s text label. This is the only sure indication of which direction an orifice plate needs to be installed. One can easily imagine an instrument technician mistaking a conical-entrance orifice plate for a square-edged, beveled orifice plate and installing it backward!

If you liked this article, then please subscribe to our YouTube Channel for Electrical, Electronics, Instrumentation, PLC, and SCADA video tutorials.

You can also follow us on Facebook and Twitter to receive daily updates.

Read Next:

  • Flow Meter Square root Relationship
  • Types of Flow Meters
  • Orifice Plate Turndown ratio
  • How an Orifice Measures Flow?
  • Orifice Flow Meter Guide
Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address
You've successfully subscribed !

Continue Reading

Magnetic Flowmeter vs. Turbine Flowmeter – Comparison
Flow Meter Installation Guidelines
Thermal Dispersion Flow Switch Working Principle
Why Flow is Directly Proportional to the Square Root of DP?
Reasons to Calibrate Different Types of Flow Meters
Metal Tube Variable Area Flow Meters Principle
Share This Article
Facebook Whatsapp Whatsapp LinkedIn Copy Link
Share
Leave a Comment

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Stay Connected

128.3kFollowersLike
69.1kFollowersFollow
210kSubscribersSubscribe
38kFollowersFollow

Categories

Explore More

What is a Flow Element? – Types, Comparison of Flow Elements
What is a Weigh Feeder?
Turbine Flow Meter Calibration
Orifice Flowmeter Rangeability
Orifice Plate Tapping – Orifice Plate Taps
Weirs and Flumes Flow Measurement
Orifice Flow Meters: Detailed Specifications
What is a Magnetic Flow Meter?

Keep Learning

Flow Meters Troubleshooting

Turbine Flow Meters Troubleshooting

orifice plate vent hole

What is the Purpose of Orifice Plate Drain Hole and Vent Hole?

Piston Type Flow Meter Principle

Types of Variable Area Flow Meters

What is an Orifice Flange ?

What is an Orifice Flange? – Purpose and Applications

Vortex Flow Meter Animation

Basic Working Principle of Vortex Flowmeter

Lobed Impeller Flow Meters Working Principle

Lobed Impeller Flow Meters Working Principle

mass flowmeters

What is a Thermal Flow Meter?

vortex flow transmitter

What is a Vortex Flow Meter?

Learn More

Siemens PLC Course for Beginners

Siemens PLC Course for Beginners: Problems and Solutions

U tube Manometer Working

Basics of Pressure

Sorting Defective Parts PLC Logic

Advanced PLC Programming for Defective Parts Sorting

Pressure Transmitters Purged impulse lines - 2

Pressure Transmitters Purged impulse lines

PLC Conversion Program

How to use Converters in PLC

Ground Rod

What is a Ground Rod?

Fiber Optic Cable - Method of Joining and Fusion Splicing

Fiber Optic Cable – Method of Joining and Fusion Splicing

Electrical Ground Loop

How to Solve Electrical Ground Loop Problems?

Menu

  • About
  • Privacy Policy
  • Copyright

Quick Links

  • Learn PLC
  • Helping Hand
  • Part Time Job

YouTube Subscribe

Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Welcome Back!

Sign in to your account

Username or Email Address
Password

Lost your password?