750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
6-21
6.18 — Low-Gas-Pressure Switch
The second cam adjusting screw may need to be adjusted in order to maintain a smooth cam profile. If all screws
are properly adjusted, none will deviate from the general overall contour of the cam face.
6.18 — Low-Gas-Pressure Switch
Adjust the scale setting to slightly below the normal burning pressure. The control circuit will be broken when
pressure falls below this point. Since gas line distribution pressure may decrease under some conditions, shutdowns
may result if the setting is too close to normal. However, regulations require that the setting may not be less than
50% of the rated pressure downstream of the regulator. Manual resetting is necessary after a pressure drop. Press
the reset lever after pressure is restored. Be sure that the mercury switch equipped control is level.
FIGURE 6-16. Gas Train Pressure Switches
6.19 — High-Gas-Pressure Switch
Adjust the scale setting to slightly above the normal burning pressure. The control circuit will be broken when
pressure exceeds the normal operating pressure. Unnecessary shutdowns may result if the setting is too close to
normal, however, regulations require that the setting may not be greater than 150% of rated pressure.
Manual resetting is necessary after a pressure rise. Press the reset lever after pressure falls. Be sure that the mercury
switch equipped control is level.
6.20 — Fuel Oil Pressure and Temperature: General
Variations in burning characteristics of the fuel oil may occasionally require adjustments to assure highest combus-
tion efficiency. The handling and burning characteristics may vary from one delivery of oil to another. Therefore, it
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