CleaverBrooks 4WI - 4.3 - Sequence of Operation: Gas or Oil; 4.3.1 - Pre-Purge Cycle

750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
4-3
4.3 — Sequence of Operation: Gas or Oil
To comply with requirements of insurance underwriters such as Factory Mutual (FM), GE GAP, or others, addi-
tional interlock devices may be used in addition to the circuits identified in section 4.2.
4.3 — Sequence of Operation: Gas or Oil
On a combination fuel unit, the gas/oil switch must be set for the proper fuel.
The following sequence occurs with power present at the program relay (PR) input terminals and with all other
operating conditions satisfied.
4.3.1 — Pre-Purge Cycle
When the burner switch (BS) is turned “on,” and controls in the “limit” and “fuel valve interlock” circuits are
closed and no flame signal is present, the “blower motor start circuit” is powered energizing the blower motor
starter (BMS). The load demand light (LDL) turns on. When firing oil, the air compressor motor starter (ACMS) (if
provided) is also powered. The air purge valve (APV) (Nos. 5 and 6 oil only) remains de-energized.
At the same time, the program relay signals the modulating damper motor (MDM) to open the air damper. The
damper begins to open and drives to its full open or high fire position. Opening the damper motor allows a flow of
purging air through the boiler prior to the ignition cycle.
On certain boilers the circuitry will include a high fire switch (HFS). The purpose of the switch is to prove that the
modulating damper motor (MDM) has driven the damper to the open position during the pre-purge cycle. In this
instance, the “high fire proving circuit” is utilized.
The controls wired into the “running interlock circuit” must be closed within 10 seconds after the start sequence.
In the event any of the controls are not closed at this time, or if they subsequently open, the program relay will go
into a safety shutdown.
Flame Detector Circuit
• Flame detector (FD)
• Main fuel valve circuit
• Man gas valve (MGV)
• Man gas vent valve (MGVV) - if provided
• Oil valve (OV)
• Main fuel valve light FVL)
Firing Rate Circuit
• Damper motor transformer (DMT)
• Modulating damper motor (MDM)
• Manual-automatic switch (MAS)
• Manual flame control (MFC)
• Modulating control (MC)
High Fire Proving Circuit
• High fire switch (HFS)
Circuit Components/Controls