boiler, feedwater heater, or surge tank. Usually, the
vacuum pump is supplied with a float switch as well as a
vacuum switch, and it can be operated as a condensate
pump unit. The float switch should be used only when
the vacuum switch is defective, and then only until the
defects can be repaired or corrected.
This system can be used in all types of buildings,
and it is of particular advantage for the satisfactory
operation of indirect radiation units, heating coils, and
ventilating units, and for other units that requires close
automatic control. Indirect radiation is a term applied to
warm-air heating systems that receive their heat from
steam supplied to their heat exchanger coils.
When considering the subject of maintenance on a
two-pipe vapor distribution system having a vacuum
pump, you will find that most of the troubles that have
previously been discussed also apply to this system. In
this distribution system, however, keeping air from
leaking into the system is more of a problem than in the
other distribution systems. Excessive air leakage often
causes the pump to run all the time, or the leakage can
cause the system to fail to heat altogether. To eliminate
-air leakage, you must find the point where air is leaking
and repair it, so air cannot get into the system. Rusty
spots and water seepage usually indicate the points at
which air is leaking into the system.
On a gravity, one-pipe, air vent system, the
return of condensate to the boiler depends on
Air in a one-pipe system has what adverse
What is the major difference between a two-pipe
system with a return trap and a two-pipe system
with a condensate pump?
What is the function of the vacuum pump on a
two-pipe vapor system?
STEAM DISTRIBUTION SYSTEM
Learning Objective: Recognize different system
components and understand their basic operation,
application, and maintenance.
In previous sections of this chapter, you read
about various components as you studied the various
distribution systems. The components were only
mentioned, however, and not explained in detail.
Therefore, in this section, we are going to discuss
these components, their purpose, operation, and
Steam radiators. are normally classified into two
categories. One is the fin-tube radiator, which consists
of a metal tube that has metal fins attached on the
outside to increase its total heating surface. It generally
has a valve at one end and a trap at the other end. This
radiator has been used more extensively in the past 15
years. It is readily adaptable to areas where floor space
is limited, since the radiator is normally mounted on the
walls. The second category is the cast-iron radiator,
which is made in sections. A typical cast-iron radiator is
shown in figure 3-9. These radiators are similar to those
used in hot-water heating systems. The cast-iron
radiator is generally used in the one-pipe distribution
system. In this system, there is only one distribution
pipe connected to the radiator. This pipe delivers steam
to the radiators, and it also returns water from the
condensed steam to the boiler. For this reason, the
radiators must be tilted slightly toward the distribution
The radiators in a two-pipe steam distribution
condenses into water.
prevents steam from leaving the radiator until it
system are connected to the boiler by means of a
distribution pipe as well as by a condensate return pipe.
Since the steam and condensate in this system flow in
separate pipes, the pipes are smaller than those required
for the same size radiator in a one-pipe system. The
radiator outlet is usually equipped with a steam trap that
Figure 3-9.A typical cast-iron radiator.