Advantages of the thermodynamic steam trap
Thermodynamic traps can operate across their entire working
range without any adjustment or change of internals.
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 waterhammer or vibration.
The all stainless steel construction offers a high degree
of resistance to corrosive condensate.
Thermodynamic traps are not damaged by freezing and are
unlikely to freeze if installed with the disc in a vertical
plane and discharging freely to atmosphere. However, operation
in this position may result in wear of the disc edge.
As the disc is the only moving part, maintenance can easily
be carried out without removing the trap from the line.
The audible 'click' which occurs as the trap opens and
closes makes trap testing very straight forward.
Disadvantages of the thermodynamic steam trap
Thermodynamic steam traps will not work positively on very
low differential pressures, as the velocity of flow across
the underside of the disc is insufficient for lower pressure
to occur. They are subjected to a minimum inlet pressure
(typically 0.25 bar g) but can withstand a maximum backpressure
of 80% of the inlet pressure.
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. Modern thermodynamic steam traps
can have an inbuilt anti-air-binding disc which prevents
air pressure building up on top of the disc and allows air
to escape, (Figure 11.4.3).
The discharge of the trap can be noisy and this factor
may prohibit the use of a thermodynamic trap in some locations,
e.g. outside a hospital ward or operating theatre. If this
is a problem, it can easily be fitted with a diffuser which
considerably reduces the discharge noise.
Care should be taken not to oversize a thermodynamic trap
as this can increase cycle times and induce wear. Mains
drainage applications often only need to be fitted with
low capacity versions, providing proper consideration is
given to siting the drain pockets correctly.