Chapter 1 — Basics of Firetube Operation
Part No. 750-184 1-7
D. STEAM CONTROLS (ALL FUELS)
1. Operating Limit Pressure Control (Figure 1-3): Breaks a circuit to
stop burner operation on a rise of boiler pressure at a selected
setting. It is adjusted to stop or start the burner at a preselected
pressure setting.
2. High Limit Pressure Control (Figure 1-3): Breaks a circuit to stop
burner operation on a rise of pressure above a selected setting. It
is adjusted to stop the burner at a preselected pressure above the
operating limit control setting. The high limit pressure control is
normally equipped with a manual reset.
3. Modulating Pressure Control (Figure 1-3): Senses changing boiler
pressures and transmits the information to the modulating motor
to change the burner firing rate when the manual-automatic
switch is set on “automatic.”
4. Low-Water Cutoff and Pump Control (Figure 1-4. 1-5): 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; also causes 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.
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.
5. Water Column Assembly: Houses the low-water cutoff and pump
control and includes the water gauge glass, gauge glass shutoff
cocks.
6. Water Column Drain Valve: Provided so that the water column
and its piping can be flushed regularly to assist in maintaining
cross-connecting piping and in keeping the float bowl clean and
free of sediment. A similar drain valve is furnished with auxiliary
low-water cutoff for the same purpose.
Figure 1-3 Steam Controls
Figure 1-4 CB Level Master (CB-LE
high pressure steam)
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