CHAPTER!
GENERAL
DESCRIPTION
AND
PRINCIPLES
OF
OPERATION
(1) Gas Pilot Valve: A solenoid valve that opens
during the ignition period
to
admit fuel
to
the
pilot.
It
closes after main flame
is
established.
The sequence
of
energizing and de-energizing
is
controlled by the programming relay. A second
gas pilot valve may be required by insurance
regulations.
(2) Gas
Pilot Vent Valve: When a secorid gas
pilot valve
is
required, a normally open vent
valve
is
installed between them. Its purpose
is
to
vent gas to the atmosphere, should any be present
in
the pilot line when the pilot valves are closed.
The valve closes when the pilot valves are ener-
gized.
(3) Gas
Pilot Shut
...off
Cock: For manually open-
ing
or
closing the gas supply to the gas pilot
valve.
(4) Gas
Pilot Adjusting Cock (Fig. 5-10):
Provided
to
regulate the size
of
the gas pilot
flame.
(5) Gas
Pilot Aspirator (Fig. 5-10): Improves the
flow
of
gas to the pilot.
(6) Gas Pressure Gauge: Indicates gas pressure
to the pilot.
(7) Gas Pressure Regulating Valve: Reduces in-
coming gas pressure
to
suit the pilot's require-
ment
of
between
5"
to
10" W
..
C.
(8) Butterfly Gas Valve: The pivoted disc
in
this
valve
is actuated by connecting linkage from the
gas modulating cam
to regulate the rate
of
gas
flow to the burner.
(9) Gas Modulating Cam (Fig. 5-6):
An
assembly
of
a series
of
adjustable allen-head screws and a
contour spring, providing for adjustment
of
gas
input at any poirit in the modulating range.
(10) Main Gas Cock: For
m~nually
opening and
closing the main fuel gas supply downstream
of
the main gas line pressure regulator. A second
shut-off cock, downstream
of
the main gas
valve(s), may be installed
to provide a means
of
shutting
off
the gas line whenever a test
is
made
for leakage across the main gas valve.
CHAPTER
1-10
(11) Main Gas Valves: Electrically actuated shut-
off
valves that open simultaneously to admit gas
to the burner. The downstream valve
is
equipped
with a "proof
of
closure" switch that
is
connected
into the pre-ignition interlock circuit.
(12) Main Gas
Vent Valve: A normally open
solenoid valve installed between the two main
gas valves
to
vent the gas to the atmosphere
should any be present
in
the main gas line when
the gas valves are de-energized. The vent valve
closes when the gas valves are energized.
(13) Low Gas
Pressure Switch: A pressure ac-
tuated switch that
is
closed whenever main gas
line pressure
is
above a preselected pressure.
Should the pressure drop below this setting, the
switch contacts will open a circuit causing the
main gas valve(s)
to
close,
or
prevent the burner
from starting. This switch
is
usually equipped
with a device that must be manually reset after
being tripped.
(14) High Gas Pressure Switch: A pressure
ac-
tuated switch that
is
closed whenever the main
gas
line pressure
is
below a preselected pressure.
Should the pressure
riSe
above this setting, the
switch contacts will open a circuit causing the
main
gas
valve(s)
to
close or prevent the burner
from
starting~
This switch
is
usually equipped
with a device that must be manually reset after
being tripped.
(15) Leakage Connection: The body
of
the gas
valve has a plugged opening that
is
used when-
ever it
is
necessary or desirous to conduct a test
for possible leakage across the closed valve.
H.
CONTROLS
COMMON
TO
OIL
FIRED
BOILERS
QNCLUDING
COMBINATION)
The following items are applicable
to
all oil fired
or gas and oil fired boilers. Additional controls
for No. 6 oil are listed in Section
I.
75()..150
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