750-91 (revised 2009)
Model CB-LE Packaged Boiler Manual
2-5
2.4 — Controls for Gas Firing
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.
Main Gas Cock For manually opening and closing the main fuel gas supply down-
stream of the main gas line pressure regulator. A second shutoff
cock, downstream of the main gas valve(s), is installed to provide a
means of shutting off the gas line whenever a test is made for leak-
age across the main gas valve.
Butterfly Gas Valve The pivoted disc in the valve is actuated by connecting linkage from
the gas modulating cam to regulate the rate of gas flow to the
burner.
Main Gas Valves Electrically actuated shutoff 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.
Low Gas Pressure Switch A pressure actuated switch that is closed whenever main gas line
pressure is above a preselected pressure. Should the pressure drop
below the setting, the switch contacts open a circuit causing the
main gas valve(s) to close, or prevent the burner from starting. The
switch is usually equipped with a device that must be manually reset
after being tripped.
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. The
switch is usually equipped with a device that must be manually reset
after being tripped.
Leakage Connection The body of the gas valve has a plugged opening that is used when-
ever it is necessary to conduct a test for possible leakage across the
closed valve.
Component Description
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