1. STEAM TRAPS
1

2. Definition
Steam trap is a type of automatic valve that filters out
condensate (i.e. condensed steam) and non-condensable gases
such as air without letting steam escape.
2

3. Why its necessary to install Steam
Traps
If condensate is not drained immediately or trapped
from the system, it reduces operating efficiency by
slowing the heat transfer process and can cause
physical damage through the phenomenon known as
"Water Hammer"
3

4. Function of Steam Traps
The job of the steam trap is to get condensate, air and Co2
out of the steam heated unit as fast as they accumulate. In
addition, for overall efficiency and economy, the trap must
also have following design and operating consideration
• Minimum steam loss
• Long life and dependable service
• Corrosion resistance
• Air venting
• CO2 venting at steam temperature
4

5. Types
Mechanical traps operate by using the difference in density
between steam and condensate. A float within the trap detects
the variance in weight between a gas and a liquid.
Thermostatic traps detect the variation in temperature between
steam and condensate at the same pressure. The sensing device
operates the valve in response to changes in the condensate
temperature and pressure.
Thermodynamic Traps use volumetric and pressure differences
that occur when water changes state into gas. These changes
act upon the valve directly.
5

6. Mechanical Steam Traps
Ball float steam trap
Inverted bucket steam trap
6

7. Ball float steam trap
Condensate reaching the trap will cause the
ball float to rise, lifting the valve off its seat
and releasing condensate
The valve is always flooded and neither steam
nor air will pass through it
Air vent allows the initial air to pass whilst the
trap is also handling condensate.
7

8. Inverted bucket steam trap
The mechanism consists of an inverted bucket which is
attached by a lever to a valve
The Method of operation is shown in a figure in next slide
(i) the bucket hangs down, pulling the valve off its seat
(ii) the arrival of steam causes the bucket to become buoyant,
it then rises and shuts the outlet.
(iii) the trap remains shut until the steam in the bucket has
condensed or bubbled through the vent hole to the top of the
trap body
8

9. 9

10. Thermostatic Steam Traps
Liquid expansion steam trap
Balanced pressure steam trap
10

11. Liquid expansion steam trap
An oil filled element expands when heated to close the valve
against the seat
The adjustment allows the temperature of the trap discharge to
be altered between 60°C and 100°C
This makes it ideally suited as a device to get rid of large
quantities of air and cold condensate at start-up
11

12. Balanced Pressure Steam Trap
The operating element is a capsule containing a special
liquid and water mixture with a boiling point below that of
water
In the cold conditions that exist at start-up, the capsule is
relaxed. The valve is off its seat and is wide open, allowing
unrestricted removal of air. This is a feature of all balanced
pressure traps and explains why they are well suited to air
venting
The vapour pressure within the capsule causes it to expand
and the valve shuts
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13. Balance Pressure Steam Traps
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14. Thermodynamic Steam Traps
Disc trap
Impulse trap
Orifice trap
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15. Disc Thermodynamic Steam Traps
The trap operates by means of the dynamic effect of flash steam as
it passes through the trap
On start-up, incoming pressure raises the disc, and cool condensate
plus air is immediately discharged from the inner ring, under the disc
Hot condensate flowing through the inlet passage into the chamber
under the disc drops in pressure and releases flash steam moving at
high velocity. This high velocity creates a low pressure area under
the disc, drawing it towards its seat
The flash steam pressure builds up inside the chamber above the
disc, forcing it down against the incoming condensate until it seats
on the inner and outer rings
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16. Disc Thermodynamic Steam Traps
16

17. Impulse steam trap
The impulse trap (as shown in Figure)
consists of a
hollow piston (A) with a piston disc (B)
working inside a tapered piston (C) which
acts as a guide. At 'start-up' the main valve
(D) rests on the seat (E) leaving a passage
of flow through the clearance between
piston and cylinder and hole (F) at the top
of the piston. Increasing flow of air and
condensate will act on the piston disc and
lift the main valve off its seat to give
increased flow. Some condensate will also
flow through the gap between the piston
and disc, through E and away to the trap
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outlet

18. Impulse steam trap
As the temperature of the condensate approaches its
boiling point some of it flashes to steam as it passes through
the gap
Although this is bled away through hole F it does create an
intermediate pressure over the piston, which effectively
positions the main valve to meet the load
When the temperature of the condensate entering the trap
drops slightly, condensate enters chamber B without
flashing into steam
18

19. Orifice Steam Traps
These are devices containing a hole of predetermined
diameter to allow a calculated amount of condensate to flow
under specific pressure conditions
They don’t have any moving pats
In case of a small orifice, the condensate flows with much
lower velocity through the opening, the much denser
condensate will stop the steam. The consequence of this is, no
fresh steam will leak through the trap
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20. Orifice Steam Traps
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21. Comparison
Mechanical
 continuous operation
 no action at no load,
continuous at full load
 good energy conservation
 good resistance to wear
 good corrosion resistance
 excellent ability to vent air
at very low pressure
 excellent operation
against back pressure
 poor resistance to
damage from freezing
 fair ability to purge
system
 excellent performance on
very light loads
 poor ability to handle dirt
 large comparative
physical size
 closed at mechanical
failure
Thermostatic











intermittent operation
fair energy conservation
fair resistance to wear
good corrosion resistance
good abilities at low
pressures
excellent operation
against back pressure
good resistance to
damage from freezing
excellent ability to handle
start-up
fair ability to handle dirt
small comparative size
open or closed at
mechanical failure
(depending on design)
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Thermodynamic
 intermittent operation
 poor energy conservation
 poor resistance to wear
 excellent corrosion







resistance
poor abilities at low
pressures
poor operation against
back pressure
good resistance to
damage from freezing
excellent ability to purge
system
poor ability to handle dirt
poor ability to handle
flash steam
open at mechanical failure