to the management. The extent of this load
change was presented at Chicago in 1955 in a
paper entitled "Extending the Pittsburgh District
Steam System to the Gateway Center Buildings" by
the writer. (NDHA Proceedings, 1955, page 48.)
be possible to pump condensate or soft water freely
in either direction from either plant as required,
it being supplied by the plan with the over-supply.
This will eliminate the dumping of excess condensate because of insufficient storage capacity.
The repairs required in the Diamond Street
tunnel, the subsequent flooding, the shutdown of
the system and the separation of the two plants
that occurred in 1957 showed that the distribution
system was in great danger. The management,
realizing then that what the operators and planners
had feared might happen, did happen; very quickly
authorized the installation of the proposed steam
lines and the completion of the loop to the triangle.
To close this major distribution loop and complete the triangle, required a steam main installation 1325 feet long, extending over three city
blocks in Penn Ave. A 16-in. high-pressure steam
line was chosen since this part of the system was
normally a part of the high-pressure system
originating at the Twelfth Street Heating plant
and would carry steam at 245 psi. With this size
line and pressure, sufficient steam could be transmitted to the lower end of the city to supplement
the Stanwix plant in carrying the load demanded
by the Gateway buildinl!s and insure service to
this important section of the city if trouble should
rlevelop on the other sections of the steam distri-bu tion main.
An 8-in. condensate line also was installed since
the condensate is returned to the plants by the
customers on the ACSH Co. system. Up to time
of the new installation, the gravity return system
was divided by a high point; all customers on the
one side returning their condensate to the Twelfth
Street Plant and those on the other side to the
Stanwix plant. This division was not always in
the most desirable proportions, either one or the
other of the plants receiving more than its share
of return water, causing make up problems at the
other. The installation of the condensate line
helped to correct in a small way this inequality.
The customers in the area through which this
installation extends are now served by other branch
lines operating at lower pressures. For this reason,
the new installation can and is considered a transmission line only, with no thought at the present
of serving steam customers from it. Since the
Twelfth Street plant generates steam at 245 psi,
the transmission line will operate at the pressure
during the heating season and through a battery
of three pressure-reducing valves in parallel, drop
the pressure fed into the lower section of the system
to the operating pressure in that area, namely 125
psi. In the summer months, the steam line will
operate at 125 psi supplying steam in a reverse
direction into the upper part at the system.
Solid-pour construction was used in this installation, this being standard with the Company.
(See Fig. 2) The total cost of the installation
amounted to $85,000. The steam and return lines
will have been in service four months when this
article appears and already the operators. are singing the praises of their many advantages. One of
the most important of these is that the Diamo~d
Street tunnel can now be repaired with less danger
of interruption of service. This removes many
anxieties from the minds of those responsible for
uninterrupted steam supply to the Company's
many customers, as the high and low-pressure steam
lines can now be removed and replaced while
major repairs are made to the forty-year old concrete tunnel in Diamond Street.
After many years of dark clouds and anxious
moments, the silver lining is beginning to show
through and the heating business in Pittsburgh
stands on a much more secure foundation for
continuity of service and ability to serve the steam
required where it is most needed.
In addition to the condensate line a
6-in. copper pipe was installed for the
transfer of condensate or soft water
between the two plants. The Twelfth
Street Plant has a high-capacity water-softening plant to provide soft water
for the system. Evaporators of small
capacity have been in use at the Stanwix
plant but they are often inadequate to
supply the demand for make-up at this
plant alone. When the installation of
the water transfer line is completed,
which will be early in 1959, it will then
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