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Couplings are used to connect Motor or other driving force to equipment's like Pump, Reactor, Compressor Etc. Couplings transfer angular rotation and torque. There are several types of coupling with specific advantages and disadvantages.

Types of couplings

Rigid coupling

  1. Sleeve coupling [Muff coupling]
  2. Clamp coupling [Split coupling/compression coupling]
  3. Flange Coupling

Flexible coupling

  1. Bushed Pin Flexible Coupling
  2. Oldhams coupling
  3. Universal coupling
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Why couplings are required?

There are several reasons that needs coupling between motor and equipment.
  • Motor generally owned by electrical department and Equipment is owned by mechanical department. 
  • Shafts are generally available in 7 meters length, More lengths are having transport issues.
  • Motor and equipment are sold in market as an individual.
  • Maintenance or failure of Equipment which requires more time of maintenance than replacement are requires replacement of Motor or Equipment for restoration and quick start up, So coupling of equipment could decouple replacement and restart process.
  • Coupling provides proper alignment between motor and equipment.

Signs of good coupling

  • Good coupling is easy to couple / decouple and alignment.
  • It should reduce or absorb transmission shock between motor or equipment
  • Less torque drop in operation.
  • Coupling should hold shafts in aligned position.

Rigid Coupling


Sleeve coupling [Muff coupling]

Sleeve coupling is simplest type coupling in rigid coupling. It's structure of hollow cylinder whose inner diameter is same of shaft's diameter. Placement of coupling is on the shafts using gib head key.

Sleeve coupling


Torque is transmitted from motor to equipment through gib key and coupling. 

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Advantages

Simple in design, It has only two parts coupling and gib key.
Cost economic 
Compact in design so transportation becomes easier.
No projecting parts so it's safe to use.

Disadvantages

It has no shock absorbing parts like spider so its make noise and vibrations.
Difficult of to assemble and disassemble dew to it's bolting
It is rigid coupling so not offering misalignment compensation.

Application

In line shafts in small pumps

2. Clamp coupling [Split coupling/compression coupling]

Clamp coupling is made of two halves and placed on shaft. after placement it is fitted with bolts.The Shaft made about and connected to each other with bolts and single key fitted directly with key ways given at shafts.

Clamp coupling  Split coupling compression coupling

Bolts are generally two, four, six or eight as per length. Nuts are necessary for fitting muff castings.  This type of coupling is used for heavy duty couplings and moderated speed.

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Advantages

Position of shafts not need to be change during decoupling.

Disadvantages

It is not used in High speed operations.

Application

Used where shafts are in line in small to moderated sze. 

3. Flange coupling

Flange coupling applied in that cases where motor and equipment has coupling. Faces are forged at right angle.

Flange coupling
Credits - IndiaMart

One flange is projected part and other is corresponding part. This arrangement helps to adjust shaft in line and stay in alimented. Flanges have spider adaptable design. Both flanges are connected with nut bolt. 

There are three types of flange couplings

1. Unprotected flange coupling

In this type of flange shafts are keyed in counter sunk key. Coupling done with nut bolts, bolts may be four six or more on sizing. Keys are made in right angle[ 90 degree] in circumference.

2. Protected flange coupling

The Protruding bolts are protected by flanges to avoid damage to workman as well as Coupling.

3. Marine type coupling

In this type of coupling Nut bolts are inside in flange. For this coupling tapered headless bolts are utilized. 

See in details


Application

All types of shafts which are in alignment. 

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Flexible coupling

Flexible coupling is used when shafts are not in exact alignment. This coupling undue misalignment. 

Types of Flexible coupling
  1. Bushed Pin Flexible Coupling
  2. Oldhams coupling
  3. Universal coupling
1. Bushed Pin Flexible coupling


Bushed Pin Flexible coupling
Credits - IndiaMart

It is an upgraded version of flange coupling. Thick Rubber bushing is provided between flanges and these are slight big in size so bolts could be placed properly. Rubber bushing absorbs shocks and vibrations.

Application

Flanges which are slight misalignment in parallel, angular and axial.

Oldham Coupling



Oldham Coupling
Credits - Autodesk

This type of coupling is used where shafts are parallel at a small misaligned distance. Both positions are both slots could connect. This coupling made with circular disk with projections either side. Torque transfer takes place due to motor and equipment shafts connected through circular disk in coupling.

Application

Printing applications

Universal coupling

Universal coupling is used where shafts are at some angle. The inclination shaft may be increase while in rotation. This type of coupling is used in automobile industry as knee type joints.

Universal coupling


Application

Generally used in Automobile Driver shaft and aircraft.

Check points of Couplings

1. All parts of coupling must be tight enough so decoupling and misalignment should be avoided.
[In reactors it will be critical and in exothermic, polymer reactors it becomes worst, In continuous process decoupling of pump may leads in unusual stoppage of plant.]

2. Whenever Preventive maintenance or shutdown takes place alignment checking should be done through laser alignment technique

Read more about "Pumps - All  types" from Industrial Guide - Click here

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Thanks for reading - Piping and Equipment's
Naitik Patel
Industrial Guide

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