distribution systems. The maintenance required on
conduit and utilidors consists of keeping the materials of
which they are constructed from being damaged and of
ensuring that water is kept out of the tunnels and pipes. The
maintenance required on outside metal coverings is about
the same as that for the conduit and utilidors.
Q1. What are the two classifications of exterior
steam distribution systems?
Q2. Conduit and utilidor steam distribution systems
are normally installed as a permanent
installation because of what reason?
What is the main disadvantage of an overhead
steam distribution system?
INTERIOR STEAM DISTRIBUTION
Learning Objective: Recognize types and
configuration of interior distribution systems.
Understand their basic installation, operation, and
Interior steam distribution systems may be classified
according to pipe arrangement, accessories used, method
of returning condensate to the boiler, method of expelling
air from the system, or the type of control used. The
interior steam systems discussed in this chapter are
classified according to pipe arrangment.
Steam may be fed to interior steam distribution
systems from a boiler in the same building or from the
exterior distribution system of a central plant.
GRAVITY, ONE-PIPE, AIR-VENT
The gravity, one-pipe, air-vent system, as shown
in figure 3-5, is one of the oldest types of internal
distribution systems. Its capacity is usually ample, and
its installation cost is low. Because the condensate is
returned to the boiler by gravity, this system is usually
confined to one building and is seldom used as a
central plant distribution system. The steam is
supplied by the boiler and is carried by a single system
of piping to the radiators. The return of condensate
depends upon the hydrostatic head. Therefore, the end
of the steam main, where the main is drained to the wet
return, should be high enough above the waterline to
provide the required hydrostatic head above the
entrance to the boiler. The radiators in the system are
equipped with an inlet valve and an air valve. The inlet
valve is the radiator shutoff valve, while the air valve
permits the venting of air from the radiators.
Condensate is drained from the radiators through the
same pipe that supplies the steam; they flow in
opposite directions, however, which is a dis-
advantage. Under certain conditions, the condensate is
held in the radiators. This causes noisy operation and a
fluctuating water level in the boiler. Water hammer and
slow heating are characteristic of this system when the
pipe sizing, pitch, and general design are inadequate.
Figure 3-5.A gravity, one-pipe, air-vent system.