750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
1-5
1.4 — Steam Controls (All Fuels)
1.4 — Steam Controls (All Fuels)
1.4.1 — Controls
1.
Operating Limit Pressure Control
: Breaks a circuit to stop
burner operation on a rise of boiler pressure at a selected set-
ting. It is adjusted to stop or start the burner at a preselected
pressure setting.
2.
High Limit Pressure Control
: 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 con-
trol is normally equipped with a manual reset.
FIGURE 1-5.
Steam Controls
3.
Modulating Pressure Control
: Senses changing boiler pressures and transmits the information to the modu-
lating motor to change the burner firing rate when the manual-automatic switch is set on “automatic.”
1.4.2 — Low Water Cutoff
The style of Low Water Cutoff is determined by the design pressure of the vessel or by cus-
tomer preference. The Level Master (for operation and maintenance information, consult
the Level Master manual that accompanied the boiler) is used on all steam boilers 150 psig
to 250 psig. The McDonnell-Millar (MM) LWCO is available on low pressure steam boilers
to 15 psig and hot water boilers to 250º F and to 125 psi. For additional information on the
Level Master, refer to the Level Master Operation and Maintenance manual, manual number
750-192.
FIGURE 1-6.
Level Master Low Water Cutoff (LWCO)
1.
Low Water Cutoff and Pump Control
: Float-operated control responds to the water level in the boiler. It per-
forms 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.
Summary of Contents for 4WI
Page 46: ...Burner Operation and Control 2 22 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
Page 62: ...Waterside Care and Requirements 3 16 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
Page 70: ...Sequence of Operation 4 8 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
Page 114: ...Adjustment Procedures 6 28 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
