Date post: | 15-Jul-2015 |
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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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