compression couplings

8/8/2019 Compression Couplings

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COMPRESSIONCOUPLINGS


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Introduction:

In the field of plumbing, there is a wide variety of

fittings and couplings that come into play. One of the

more useful and versatile of these is the compression

coupling. A compression coupling is a unique type of

fitting used to connect tubing. These fittings are used in

fluid and gas applications.


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Definition ofCoupling:

A coupling is a device used

to connect two shafts together at

their ends for the purpose of

transmitting power. Couplings

do not normally allow

disconnection of shafts during

operation, however there are

torque limiting couplings which

can slip or disconnect when

some torque limit is exceeded.


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Purpose ofCoupling:

The primary purpose of couplings is to join two

pieces of rotating equipment while permitting some

degree of misalignment or end movement or both. By

careful selection, installation and maintenance of

couplings, substantial savings can be made in reduced

maintenance costs and downtime.


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What is Compression Coupling?

Definition:

A means of connecting two perfectly aligned shafts

in which a slotted tapered sleeve is placed over the

junction and two flanges are drawn over the sleeve so

that they automatically center the shafts and provide

sufficient contact pressure to transmit medium loads. A

type of tubing fitting.


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Materials, Sizeand Shapes

Compression couplings are manufactured from

various materials, including Brass, Copper, Plastic and

Cast Iron. The most common compression couplings

are made ofbrass. They also are available in a variety

of shapes and sizes. The size of a compression coupling

is determined by the outside diameter of the tube or pipe

it holds.


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Types ofCompression Coupling:

There are Two Types of compression couplings.

Type A, referred to as non-manipulative, is used in

fluid plumbing systems.

Type B, known as a manipulative fitting, is found in gasapplications.


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Working Process:

A compression coupling works by using clamping

force to seal the fitting. The unit consists of a

compression nut, a compression ring and a seat. The

compression ring, often called a ferrule, is placed on the

tubing with the nut behind it. The tubing is then inserted

into the seat, and the nut is screwed onto the seat. As

the nut is tightened, it compresses the ring around the

tubing, creating a leak-free seal.


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A multi-port compression coupling can be used

when it is necessary to connect more than two

lines. These are very useful in adding additional

water or gas outlets to an existing system.

Compression couplings also are manufactured as

combination fittings. Combination fittings have a

compression coupling on one end and another type

of fitting, such as a straight pipe nipple, on the

other end. These types of fittings serve to connect

different types of tubing and pipe.


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Requirements ofGood Coupling Setup

It should be easy to connect or disconnect the

coupling.

It should transmit the full power from one shaft to

other without losses.

It does allow some misalignment between the two

adjacent shaft rotation axis.


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Rubber in Compression Coupling


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It is the goal to minimise the remaining misalignment in

running operation to maximise power transmission and

to maximise machine runtime (coupling and bearing and

sealings lifetime).

It should have no projecting parts.

It is recommended to use manufacturer's alignment

target values to set up the machine train to a defined

non-zero alignment, due to the fact that later when the

machine is at operation temperature the alignment

condition is perfect


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Tools to measureaxis alignment condition:

it is possible to measure the alignment with dial gauges

or feeler gages using various mechanical setups.

it is recommended to take care of bracket sag, parallaxe

error while reading the values.

it is very convenient to use laser shaft alignment

technique to perform the alignment task within highest

accuracy.

it is required to align the machine better, the laser shaft

alignment tool can help to show the required moves at

the feet positions.


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Compression Coupling Maintenance

and Failure:

Coupling maintenance is generally a simple matter, requiring a

regularly scheduled inspection of each coupling. It consists of:

Performing visual inspections, checking for signs of wear or

fatigue, and cleaning couplings regularly.

Checking and changing lubricant regularly if the coupling is

lubricated. This maintenance is required annually for most

couplings and more frequently for couplings in adverse

environments or in demanding operating conditions.

Documenting the maintenance performed on each coupling,

along with the date.


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Even with proper maintenance, however, couplings can fail.

Underlying reasons for failure, other than maintenance, include:

Improper installation

Poor coupling selection

Operation beyond design capabilities.

The only way to improve coupling life is to understand what

caused the failure and to correct it prior to installing a new coupling.

Some external signs that indicate potential coupling failure include:

Abnormal noise, such as screeching, squealing or chattering

Excessive vibration or wobble

Failed seals indicated by lubricant leakage or contamination.


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Checking the Coupling Balance:

Couplings are normally balanced at the factory prior

to being shipped, but they occasionally go out of balance

in operation. Balancing can be difficult and expensive,

and is normally done only when operating tolerances are

such that the effort and the expense are justified. The

amount of coupling unbalance that can be tolerated by

any system is dictated by the characteristics of the

specific connected machines and can be determined by

detailed analysis or experience.


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Uses ofCompression Coupling To provide for the connection of shafts of units that are

manufactured separately such as a motor and generator

and to provide for disconnection for repairs or alternations.

To provide for misalignment of the shafts or to introduce

mechanical flexibility.

To reduce the transmission of shock loads from one shaft to

another.

To introduce protection against overloads.

To alter the vibration characteristics of rotating units.

To transmit the cent percent power


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compression couplings

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