750-96 (revised 2010)
Model CB Packaged Boiler Manual
5-17
5.9 — Low Gas Pressure Switch
Through the manual flame control switch, position the cam so that the adjusting screw adjacent to the end or high
fire screw contacts the cam follower. Make a combustion analysis at this point. If an adjustment is necessary, turn
the adjustment screw accordingly to increase or decrease fuel flow. Take a combustion reading to verify input.
Repeat as necessary until the desired flow is obtained.
Repeat this process, stopping at each adjusting screw until low fire position is reached. If all screws are properly
adjusted, none will deviate from the general overall contour of the cam face. It may be necessary to readjust the
setting of the low fire stop screw in order to obtain proper air fuel ratio at low fire burning rate. To insure that the
low fire position of the butterfly valve is always the same, allow one turn of the stop screw for over-travel.
5.9 — Low Gas Pressure Switch
Adjust the scale setting to slightly below the normal burning pressure. The control circuit will be broken when pres-
sure 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. Make sure
that a mercury switch equipped control is level.
5.10 — High Gas Pressure Switch
Adjust the scale setting to slightly above the normal burning pressure. The control circuit will be broken when pres-
sure exceeds this point. Unnecessary shutdowns may result if the setting is too close to normal, however, regula-
tions require that the setting may not be greater than 50% of the rated pressure.
Manual resetting is necessary after a pressure rise. Press the reset lever after pressure falls. Make sure that a
mercury switch equipped control is level.
5.11 — Fuel Oil Pressure and Temperature: General
Variations in burning characteristics of the fuel oil may require adjustments from time to time to assure highest
combustion efficiency. The handling and burning characteristics may vary from one delivery of oil to another. For
this reason it is recommended that the oil system be inspected from time to time to verify that pressures and vis-
cosity are at the proper operating levels.
Because of variation in oils including chemical content, source, blends, and viscosity characteristics, the tempera-
tures and pressures listed in Chapter 4 and mentioned in the adjusting of the controls in the following paragraphs
will vary and thus may be regarded as tentative and to be changed to provide best firing conditions. The Oil Viscos-
ity Chart (Figure 5-7) may be used as a guide, although your oil supplier will be able to give you more exacting
information based on an analysis of the oil.
NOTE: Do not use any lubricant on the adjusting setscrews. These have a nylon locking insert intended to provide lock-
ing torque and resistance to loosening.
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