Page 274 - Boiler plant and distribution system optimization manual
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Steam Traps 259
Most facilities will require several types of
steam traps in various sizes to provide efficient
steam trapping. The user must have knowledge
of the various types of traps available to properly
select and specify the traps to be used.
Categories of Steam Traps
All steam traps are designed to distinguish
between condensate and steam. To be effective
they must stop or trap the steam and release con-
densate. The physical differences between steam
and condensate has lead to a variety of approach-
es to steam trap design.
There are three basic categories of steam
traps, each using a different principle to differ-
entiate between steam, non-condensible gas and
condensate. These are:
Mechanical, which are operated by differ-
ences in density between steam and conden-
sate.
Thermodynamic, operated by kinetic ener-
gy.
Thermostatic, operated by temperature.
Mechanical Steam Traps
Mechanical steam traps are operated by the
difference in density between steam and conden-
Figure 14.7—various ways a steam trap can waste sate. All use a float in some form to operate the
steam: (a) is either failure to close completely or clos-
ing too slowly, (b) is leaking in the closed position valve to let condensate drain from the system.
and (c) trap fails open. Mechanical traps include Inverted Bucket,
Open Bucket and Float and Thermostatic (F&T)
types. All can operate at or near steam saturation
temperature because trap operation is dependent
STEAM TRAP TYPES AND on the density difference between steam and wa-
CHARACTERISTICS ter which is about 700 to 1. Figure 14.8 shows the
density relationship between water and steam.
Effective steam trapping practices have a di- All mechanical traps respond quickly to
rect impact upon the efficiency of any steam or changing loads and most have large turn down
condensate system. ratios. However, without a separate mechanism
To ensure maximum steam trap life and to discharge air and non-compressible gasses,
steam system efficiency, steam trap type and size mechanical traps have a limited venting capacity.
must be properly matched to each application. It Since all mechanical traps depend on a con-
is important to emphasize there is no “UNIVER- densate level inside the trap for proper operation,
SAL” steam trap which will provide efficient op- they are position sensitive. Some will fail to oper-
eration for all applications. ate when installed even a little off vertical.
