Basics of Firetube Operation
1-6
750-91 (revised 2009)
Model CB-LE Packaged Boiler Manual
1.4.3 — Modulating Pressure Control
Senses changing boiler pressures and transmits the information to the modulating motor to change the burner fir-
ing rate when the manual-automatic switch is set on “automatic.”
FIGURE 1-3. Boiler Controls
1.4.4 — Low Water Cutoff and Pump Control
Float-operated control responds to the water level in the boiler. It performs two distinct functions:
• Stops firing of the burner if water level lowers below the safe operating point. Energizes the low-water light in
the control panel, and it also causes the low-water alarm bell (optional equipment) to ring. Code requirements of
some models require a manual reset type of low-water cutoff.
• Starts and stops the feedwater pump (if used) to maintain water at the proper operating level.
The CB Level Master is the standard low water cutoff on high pressure steam boilers. See CB manual 750-281 for
complete operation, maintenance, and parts information.
1.4.5 — Water Column Assembly
Houses the low-water cutoff and pump control and includes the water gauge glass and gauge glass shutoff cock.
Determine that the main and auxiliary low water cutoffs and pump control are level after installation and throughout
the equipment’s operating life. Failure to follow these instructions could result in equipment damage.
!
Caution
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