DIFFERENT TYPES OF STREAM TRAPS

Prem Baboo

Sr. Manager (Prod)

National Fertilizers Ltd. India

F.I.E., Institution of Engineers (India)

Technical Advisor & an Expert for

www.ureaknowhow.com

STEAM TRAP

The purpose of a steam trap is not as the

name may indicate to trap steam, but rather to

trap condensate in a steam line.

The trap should be closed when steam is

present in the line.

It is usually important that the traps perform

closing and opening quickly to reduce steam

and condensate losses.

There are three types of

steam traps, they are:

1. Ball float & bucket traps are mechanical steam traps.

They operate be response to the difference density between and steam and

condensate

2. Thermostatic steam traps operate by noticing the

temperature difference between condensate and steam.

3. Thermodynamic traps operate by the difference in

thermodynamic energy between steam and condensate.

Mechanical steam traps.

Ball Float Trap

Inverted Bucket Float

Open Bucket Float

Ball float steam trap

Ball Float Steam Trap

Open Bucket Float

Open Bucket Float

Advantages

Discharge condensate continuously as rapidly as its forms.

High air venting capacity through auxiliary balanced- pressure air vent. Which is self adjusting for varying steam pressure.

High thermal efficiency at both light and heavy loads.

Steam lock release facility available.

Fair resistance to water hammer.

Wide range of orifices to suit in let pressure.

Limitations

Can not be used on high degree of

superheat.

Application subjected to freezing must be

protected with insulation and S L R.

Water hammer can damage the float.

Typical Applications:

Air unit heater.

Hot water heater.

Heat exchangers

Converters

Reboilers

Jacketed pans

Inverted Bucket Float

Main valve

Inverted bucket

Inverted Bucket Float

Advantages

Fair resistance to water hammer.

Can be made for high pressures.

Limitations

Low thermal efficiency under varying loads and pressures, some steam loss for operation.

Must maintain water seal to avoid continuous discharge of steam.

Must be protected from freezing.

Cannot discharge condensate continuously as it forms.

Typical Application.

High pressure indoor steam main drips and

submerged heating coils.

Operation

Liquid expansion steam trap

Balanced pressure steam trap

Bimetallic steam trap

Thermostatic Steam Traps

Liquid expansion steam trap

Installation of a liquid

expansion steam trap

Advantages

It is able to withstand vibration and

water hammer conditions.

Prevents flooding of heating surface

during cold startup.

Liquid expansion traps can be adjusted

to discharge at low temperatures,

giving an excellent 'cold drain' facility.

Limitations

Not pressure balance.

Since the liquid expansion trap discharges condensate at a temperature of 100°C or below, it should never be used on applications which demand immediate removal of condensate from the steam space.

The liquid expansion trap is not normally a trapping solution on its own, as it usually requires another steam trap to operate in parallel.

Balanced pressure steam trap with

replaceable capsule

Balanced pressure capsule arrangement

Operation of balanced

pressure steam trap capsule

Advantages

High air venting capacity for fast startups.

Self adjusting to all pressures within its range.

Sealed capsule is free from maintenance.

Doubles as an air vents and vacuum breaker.

The valve is fully open on start-up, allowing air and other non-condensable gases to be discharged freely and giving maximum condensate removal when the load is greatest.

Trap maintenance is simple. The capsule and valve seat are easily removed, and replacements can be fitted in a few minutes without removing the trap from the line.

Limitations

In common with all other thermostatic traps, the balanced pressure type does not open until the condensate temperature has dropped below steam temperature (the exact temperature difference being determined by the fluid used to fill the element). This is clearly a disadvantage if the steam trap is chosen for an application in which water logging of the steam space can not be tolerated, for example; mains drainage, heat exchangers, critical tracing.

Typical Application:

Steam radiators

Steam tracer and jacketed pipe .

Air venting of process equipment Steam

heater.

Bimetallic steam trap

Response of a single element

bimetal steam trap

Bimetal steam trap with two

leaf element

Response of a two leaf element

Multi-cross elements of

bimetallic steam traps

Advantages

Bimetallic steam traps are usually compact, yet can have a large condensate capacity.

Good air venting capability and maximum condensate discharge capacity under 'start-up' conditions.

Bimetallic steam traps are usually able to withstand water hammer, corrosive condensate, and high steam pressures.

Maintenance of this type of steam trap presents few problems, as the internals can be replaced without removing the trap body from the line.

Limitations

Bimetallic steam traps are not suitable for

fitting to process plants where immediate

condensate removal is vital for maximum

output to be achieved

Bimetallic steam traps do not respond

quickly to changes in load or pressure

because the element is slow to react.

Bimetallic steam traps

Bimetallic steam trap with

cooling leg

Thermodynamic Steam Traps

Traditional thermodynamic steam trap

Impulse steam trap

Labyrinth steam trap

Fixed orifice traps

Thermodynamic steam trap

Advantages

They are compact, simple, lightweight and have a

large condensate capacity for their size.

Thermodynamic traps can be used on high

pressure and superheated steam and are not

affected by water hammer or vibration.

As the disc is the only moving part, maintenance

can easily be carried out without removing the

trap from the line.

Limitations:

Thermodynamic steam traps will not work

positively on very low differential pressures.

Thermodynamic traps can discharge a large

amount of air on 'start-up' if the inlet pressure

builds up slowly. However, rapid pressure build-

up will cause high velocity air to shut the trap in

the same way as steam, and it will 'air-bind'. In

this case a separate thermostatic air vent can be

fitted in parallel with the trap

Impulse steam trap

Advantages

Impulse traps have a substantial condensate handling capacity for their size.

They will work over a wide range of steam pressures without any change in valve size and can be used on high pressure and superheated steam.

They are good at venting air and cannot 'air-bind'.

Limitations:

Impulse traps cannot give a dead tight shut-off

and will blow steam on very light loads.

They are easily affected by any dirt which enters

the trap body due to the extremely small

clearance between the piston and the cylinder.

The traps can pulsate on light load causing noise,

water hammer and even mechanical damage to

the valve itself.

Labyrinth steam trap

Advantages

This type of trap is comparatively small in

relation to its capacity and there is little

potential for mechanical failure since there

are no automatic parts.

Limitations:

The labyrinth trap has to be adjusted

manually whenever there is a significant

variation in either steam pressure or

condensate load

Ball-float steam trap

Bucket-type steam trap

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