750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
2-7
2.5 — Controls for Gas Firing
FIGURE 2-7. Burner Drawer Face and Gas Modulating Cam
8. 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.
9. 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 con-
tacts 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.
10. 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.
11. Gas Pilot Aspirator Provides complete mixing of gas and air to the pilot.
12. Gas Pilot Adjusting Cock Regulates the size of the gas pilot flame.
13. Gas Modulating Cam As 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.
14. Butterfly Gas Valve The pivoted disc in the valve is actuated by connecting linkage from the gas modu-
lating cam to regulate the rate of gas flow to the burner.
15. Leakage Connection The body of the gas valve has a plugged opening that is used whenever it is neces-
sary to conduct a test for possible leakage across the closed valve.
Component/Control Description
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