Drip Traps For Distribution Pipes - Xylem Bell & Gossett Hoffman Speciality Series Engineering Data Manual

Drip Traps for
Distribution
Pipes
20
Drip Traps for Steam Distribution Piping
The steam distribution piping, often referred
to as steam mains, provides the link between
the boiler and the steam utilizing equipment.
The steam piping must be kept free of air and
condensate. This requirement is met with the
use of steam traps installed in the piping. The
traps used for draining the steam mains are
commonly referred to as drip traps. If the
steam mains are not adequately trapped the
results are often water hammer in the piping.
Water hammer is caused by slugs of conden-
sate traveling at high speed in the steam
pipes, which can damage valves and piping.
Drip traps are installed in the steam mains at
all risers, ahead of all reducing valves, ahead
of all regulators, at the end of mains, through-
out the piping at intervals at least every 500
feet, at expansion joints and at all steam
separators.
The size and type of drip traps used will
depend on the method used in heating the
steam mains to final pressure and tempera-
ture. The two methods commonly used are
automatic start-up and supervised start-up.
In systems using automatic start-up the
steam boiler is used to bring the mains up
to final pressure and temperature without
supervision. The drip traps must handle the
full condensing load during start-up of the
system.
In systems using supervised start-up the oper-
ator opens manual valves in the steam piping
before steam is admitted to the system.
When the system reaches normal pressure
and temperature, the manual valves are
closed. The drip traps for supervised start-up
are sized only for the running load.
The sizing of drip traps will depend on the
type of start-up used. During the initial start-
up of automatic startup systems, a large
amount of condensing occurs, bringing the
steam piping from ambient temperature up to
the final steam temperature.
When supervised start-up is used the drip trap
is sized only to handle the heat loss through
the steam piping.