750-96 (revised 2010)
Model CB Packaged Boiler Manual
1-9
1.8 — Controls for Gas Firing
5. Gas Pilot Aspirator Improves flow of gas to the pilot.
6. Gas Pressure Gauge Indicates gas pressure to the pilot.
7. Gas Pressure Regulat-
ing Valve
Reduces incoming gas pressure to suit the pilot’s requirement 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 An assembly, consisting of a quadrant, a series of adjustable allen-head screws, and a
contour spring, provided for adjustment of gas input at any point in the modulating range.
10. Main Gas Cock For manually opening and closing the main fuel gas supply downstream of the main gas
line pressure regulator. A second shutoff 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.
11. Main Gas Valves An electrically actuated shutoff valve. when open, it admits main flame gas through the
butterfly (modulating) gas valve. The valve may be equipped with a “proof of closure”
switch connected into a pre-ignition interlock circuit. A second motorized shutoff gas
valve is often used. Item 12 is also used when required.
12. Main Gas Vent Valve A normally open solenoid valve installed between the two main gas valves to vent 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 actuated switch that is closed whenever main gas line pressure is above a pre-
selected 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 actuated switch that is closed whenever main gas line pressure is below a
preselected pressure. Should the pressure rise above the 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 whenever it is necessary or
desirous to conduct a test for possible leakage across the closed valve.
Control Description
Courtesy of: C3 Surplus LLC
Surplus Industrial Superstore
305-428-2777
https://www.c3surplus.com
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