750-392
CBEX-DE
1-5
Component Locations
1.2.3 — Main gas train
Depending upon the requirements of the insurance carrier or other governing agencies, the gas train may consist
of some or all of the following items.
1. Shutoff Cocks: 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), is installed to provide a
means of shutting off the gas line whenever a test is made for leakage across the main gas valve.
2. Main Gas Valve: Double body safety shutoff valve. Electrically actuated valves open simultaneously to admit
gas to the burner. The downstream valve is equipped with a with a regulating actuator and a proof of closure
switch that is connected to the pre-ignition interlock circuit.
3. Main Gas Vent Valve (if required): 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 deener-
gized. The vent valve closes when the gas valves are energized.
4. Low Gas Pressure Switch: A pressure-actuated switch; closed whenever main gas line pressure is above a pre-
selected 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.
5. High Gas Pressure Switch: A pressure actuated switch; 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 caus-
ing 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.
6. Test Cocks: The body of the gas valve has 1/4-inch NPT fittings for pressure test connection.
7. Butterfly Gas Valve (not shown): The pivoted disc in the valve is directly driven by a servo motor actuator to
regulate the rate of gas flow to the burner. In optional 700-800 HP single point systems, the valve is driven by
the modulating motor through connecting linkage.
FIGURE 1-6. Main gas train
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