CHAPTER2
A rule
of
thumb
of
Vz
to 1 GPM per boiler
horsepower can
be
used
to
determine the mini
..
mum continuous flow rate through the boiler
under all operating conditions.
The operator should determine that a flow
of
water exists through the boiler before initial
firing
or
refiring after the boiler has been drained.
Water
Circulation
The chart in Fig. 2-1 shows the maximum GPM
circulation rate
of
boiler water in relation to full
boiler output and system temperature drop.
Multiple Boiler
Installations-
When multiple
boilers
of
equal
or
unequal size are used, care
must
be taken to ensure adequate
or
proportional
flow through the boilers. This can best be
ac-
complished by use
of
balancing cocks and gauges
in
the supply line from each boiler.
If
balancing
cocks or orifice plates are used, a significant
pressure drop (e.g., 3-5 psi) must
be
taken across
the balancing device to accomplish this purpose.
If
care
is
not taken to ensure adequate
or
propor·
tiona! flow through the boilers, this can result in
wide
variations in firing rates
between
the
boilers.
In
extreme cases, one boiler may be
in
the high
fire position, and the other boiler or boilers may
be at low fire. The net result would
be
that the
common header water temperature to the system
would not be up
to the desired point. This
is
an
important consideration in multiple boiler
instal-
lations.
Pressure Drop
Through
Boiler - There will
be a pressure drop
of
less than three feet head
(1
psi - 2.31 ft. hd.) through all standard equipped
Qeaver-Brooks boilers operating in any system
which has more than a
10°F temperature drop.
Pump
Location - It is recommended that the
system circulating pumps take suction from the
outlet connection on the boiler and that they
discharge
to
the system load. This puts the boiler
and the expansion tank on the suction side
of
the
pump. This location is preferred because
it
decreases air entry into the system and does not
impose the system head on the boiler.
CHAPTER 2-4
THE
PRESSURE VESSEL
It
is
common practice to install a standby system
circulating pump. The main circulating pump
usually
is
located adjacent to the boilers
in
the
boiler room.
Pump
Operation-
Pumps are n9rmally started
and stopped by manual switches. It
is
also
desirable to interlock the pump with the burner
so that the burner cannot operate unless the
cir-
culating pump
is
running.
Pressure
The design
of
the system and the usage require-
ments often will dictate the pressure exerted upon
the boiler. Some systems are pressurized with air
or with an inert gas, such as nitrogen. Caution
must
be
exercised to make sure that the proper
relationship
of
pressure to temperature· exists
within the boiler so that all
of
the boiler's internal
surfaces are fully wetted at all times.
It
is
for this
reason that the internal boiler pressure,
~
indi-
cated on the water pressure gauge, must be held
to
the level shown in Fig. 2-2.
When initially firing a 'newly installed boiler or
when .bringing an existing boiler into an
operat-
ing system, the boiler
or
boilers to
be
brought on
line
MUST
be
pressurized equal
to
the system
and/or other boilers prior
to
opening the header
valves.
It
is
advisable to have a thermometer installed
in
the return line to indicate return water tempera-
ture. With this determined and with the supply
water temperature
to
system known, the tempera-
ture
differential
will
be
established.
With
knowledge
of
the pumping rate, the operator
easily can detect any excessive load condition
and take appropriate corrective action (see Fig.
2-1).
Special
caution must be taken
to
guard against
any
conditio~
or combination
of
conditions,
which might
·lead to the transfer
of
cold water to
a hot boiler
or
hot water
to
a cold boiler. This
particularly
is true in the case
of
boilers that are
operated for purposes other than supplying hot
750-150
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