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Thermodynamic Steam TrapApril 30, 2014 5:31 am | Leave a Comment | Frozee

Steam traps are special types of valves which prevent the passage of steam but allow condensate

through. It works automatically and is used in steam heating lines to drain condensate without passing

any steam. The benefit gained with a steam trap, is that steam is contained in the heating line until it

condenses, thus giving up all of its latent heat.

Thermodynamic steam traps use pressure energy of the steam to close the valve which consists of a

simple metal disc. The sequence of operation is shown in figure below.

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In (i), disc A is raised from seat rings C by incoming pressure allowing discharge of air and

condensate through outlet B. As the condensate approaches steam temperature it flashes to steam

at the trap orifice. This means that the rate of fluid flow radially outwards under the disc is greatly

increased. There is thus an increase in velocity and a reduction in static pressure. The disc is

therefore drawn towards the seat. Due to this alone the disc will never seat. However, steam can flow

round the edge of the disc resulting in a pressure build up in the control chamber D as shown in (ii).

When the steam pressure in chamber D acting over the full area of disc (iii) exceeds the incoming

Scavenge Port Inspection onboard

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Shell and Tube Freshwater Generator

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condensate / steam pressure acing on the much smaller inlet area, the disc snaps shut over the

orifice. This snap action is important. It eliminates any possibility of wire-drawing the seat, while the

seating itself is tight, ensuring no leakage. As shown in (iv) the incoming pressure will eventually

exceed the control chamber pressure and the disc will be raised, starting the cycle all over again.

The rate of operation depends upon he steam pressure and ambient air temperature. In practice, the

trap will usually open after 15 25 seconds; the length of time open depends on the amount of

condensate to be discharged. If no condensate have been formed, then the trap snaps shut

immediately. From the foregoing it will be seen that the trap is never closed for more than 15 25

seconds, so condensate is removed virtually as soon as it is formed.

References

REEDS GENERAL ENGINEERING KNOWLEDGE FOR MARINE ENGINEERS, by Leslie Jackson and

Thomas D. Morton

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Posted in: Boilers | Tagged: steam trap, thermodynamic steam trap

Remote Water Level Indicator for BoilersApril 30, 2014 5:27 am | Leave a Comment | Frozee

There are different types of remote water level indicators. Their purpose is to bring the water level

reading to some convenient position in the engine or boiler room where it can be distinctly seen.

These indicators when fitted are normally in addition to the normal statutory requirements for water

gauge fittings for boilers.

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Remote Water Level Indicator

Figure above is a diagrammatic arrangement of the Igema remote water level indicator. The lower

portion of the U tube contains a red coloured indicating fluid which does not mix with water and has a

density greater than that of water.

The equilibrium condition for the gauge is H = h + x, where is the density of the indicating fluid.

H, h, and x are variables.

If the water level in the boiler falls, h will be reduced, x will be increased and H must therefore be

increased. The level of the water in the condenser reservoir being maintained by condensing steam.

If the water level in the boiler rises, h will be increased, x will be reduced and H must therefore be

reduced. Water will therefore flow over the weir in the condenser reservoir in order to maintain the

level constant.

A strip light is fitted behind the gauge which increases the brightness of the red indicating fluid, which

enables the operator to observe at a glance from a considerable distance whether the gauge is full or

empty.

References

REEDS GENERAL ENGINEERING KNOWLEDGE FOR MARINE ENGINEERS, by Leslie Jackson and

Thomas D. Morton

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Posted in: Boilers | Tagged: remote water level indicators



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