CHAPTER I GENERAL DESCRIPTION AND PRINCIPLES OF OPERATION
(3)
High
Limit
Pressure
Control (Fig. 1-1 ):
Breaks a circuit to stop the burner operation
on
a
rise
of
pressure above a selected setting. It is
adjusted
to
stop the burner at a preselected pres-
sure above the operating limit control setting.
This control
is
normally equipped with a manual
reset.
(4) Modulating Pressure Control (Fig. 1-1):
Sen-
ses the changing boiler pressures and transmits
this information to the
modulating
motor to
change the
burner's
firing rate
when
the manual-
automatic switch is
set
on
automatic.
(5)
Low
Water
Cutoff
and Pump Control (Fig.
1-1): This float-operated control responds to the
water level in the boiler. It performs two distinct
functions:
(a)
Stops the
fuing
of
the burner
if
the
water level drops below a safe operating
level and energizes the low water light in
the control panel; it also causes the low
water alarm bell
(optiOI~al
equipment) to
ring. Code requirements
of
some
models
require a manual reset. type.
of
low water
cutoff. This type requires manual
re8et-·
ting to start the burner after a low water
shutdown.
·
(b) Starts and stops the feed water pump
(if
used) to maintain water at the proper
operating level.
CAUTION!
Determine
that
·the
main
and
auxiliary
low
water
cutoffs
and
pump
control
are level
after
in-
stallation
and
throughout
the
equipment's
operating
life
to
avoid
damage
to
the
equipment.
(6) Auxiliary Low Water
Cutoff
(Not Shown)
(Optional Equipment): This control breaks the
circuit to stop the burner operation in the event
the boiler water drops below the master low
750-150
water
cutoff
point. Manual reset type (optional
equipment) requires manual resetting in order
to
start the burner after a
low
water condition.
(7)
Low
Water Pump Control Instruction Plate
(Fig. 7-1): Gives instructions and information for
operation
of
low water devices.
(8) Water Column (Fig. 1-1): This assembly
houses the low water
cutoff
and pump control
and includes the water gauge glass, gauge
gl~
shutoff
cocks, and trycocks.
(9) Water Column Drain Valve (Fig. 1-1): The
water column drain valve is provided so that the
water
column
and its
piping
can
be flushed
regularly
to assist in maintaining cross-connect-
ing piping and
to keep the float bowl clean and
free
of
sediment. A similar drain valve is fur-
nished with the auxiliary low water cutoff (
op-
tional equipment) for the
same
purpose.
(10) Water Gauge Glass Drain Valve (Fig. 1-1):
This valve
is
provided to flush the gauge glass.
(11) Test Valve (Fig. 1-1): This valve allows the
boiler
to be vented during filling, and facilitates
routine boiler inspection.
(12) Safety Valve (Fig. 1-1):
The
purpose
of
the
valve(s)
is to prevent pressure buildup
over
the
design pressure
of
the pressure vessel.
The
size
rating and number
of
valves
on
a boiler is deter-
mined by the
ASME
Boiler Code.
The
safety
valves and their escape piping
shown
in (Fig.
1-9) are to
be installed to conform to the
ASME
code requirements.
The
installation
of
a valve
is
of
primary importance to its service life. A valve
must
be
mounted in a vertical position
so
that
discharge piping and code-required drains can be
properly piped
to prevent build up
of
back
pres-
sure an accumulation
of
foreign material around
the
valve
seat
area.
Apply
only
a moderate
amount
of
pipe compound to male threads and
avoid overtightening as this
can
dis
toft
the seats.
Use
only
flatwjawed
wrenches
on
the flats
provided.
When
installing a flange-connected
valve use a new gasket and draw the mounting
bolts
down
evenly. Do not install
or
remove side
outlet valves by using a pipe
or
wrench
in
the
outlet
CHAPTER 1·7
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