Sequence Of Operation - Weil-McLain 2 Series Supplemental Instructions

Operation, Wiring Diagrams, Trouble Shooting
HE (Series 2) and VHE (Series 2) With White-Rodgers Cycle-Pilot®
For Natural Gas Firing
BOILER EQUIPMENT COMPONENTS
BLOWER MOTOR
120/60/1,3450 RPM permanent split capacitor motor with ca¬
pacitor start and internal overload protection provides rota¬
tion of induced draft fan.
FAN (BLOWER WHEEL)
Develops induced draft to supply combustion air to boiler.
PRE-PURGE TIMER
Provides 30 second pre-purge prior to pilot ignition.
HIGH TEMPERATURE LIMIT CONTROL
In the event of high boiler water temperature, shuts down fan
and burners but allows circulator to run as long as there is a
call for heat from thermostat.
PRESSURE SWITCH
Detects pressure differential across fixed metering orifice to
prove air flow through boiler.
COMBINATION PRESSURE AND
TEMPERATURE GAUGE
Provides readings of boiler water pressure and temperature.
COMBINATION RELAY RECEPTACLE,
JUNCTION BOX AND TRANSFORMER
120/24 VOLT 40 VA transformer provides low voltage for con¬
trol circuit. Relay receptacle for plug-in circulator relay. Ter¬
minal strip for control circuit wiring.
PLUG-IN CIRCULATOR RELAY
Provides contact to energize circulator and fan and contact to
prove operation of pressure switch.
ASME SAFETY PRESSURE RELIEF VALVE
Provides safety discharge in the event boiler water pressure
exceeds 30 PSIG.
FILL-TROL SYSTEM (TYPES P-HE AND P-VHE ONLY)
Includes compression tank with permanent air cushion and
combination manual shut-off valve, check valve, pressure re¬
ducing valve and strainer for automatic filling and
maintain,
ing minimum system pressure.
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AUTOMATIC AIR VENT (TYPES P-HE AND P-VHE ONLY)
Vents air from boiler built-in air
eliminator
tapping.
GAS VALVE
Incorporates a pilot/redundant solenoid valve, integral pres¬
sure switch to sense incoming gas pressure, pressure regula¬
tor, main valve operator and socket to accept plug-in Mercury
Flame Sensor.
MERCURY FLAME SENSOR
Consists of sensing bulb, capillary tube and diaphragm filled
with mercury and connected to SPDT switch. Heat from pilot
vaporizes mercury causing diaphragm to snap switch.
RELITE CONTROL
Provides spark to light pilot.
PILOT BURNER ASSEMBLY
Includes spark ignition pilot with mercury flame sensing
probe.
THERMAL FUSE ELEMENT (TFE)
Provides safety shutdown of burners and pilot if flame is not
contained in firebox.
DRAIN VALVE
Used to drain boiler if necessary.
CIRCULATOR
Provides forced water circulation to hot water heating system.
SEQUENCE OF OPERATION
Referring to Ladder Diagram, Page 5.
1. Thermostat closes, activating relay CR (through pressure
switch). Contacts CR1 and CR2 close:
a) CR2 activates circulator.
b) Blower is activated through limit switch.
c) CRl provides a bypass around pressure switch to prove
its operation.
2. When adequate draft is proven by pressure switch, the 30
second pre-purge timer starts.
3. After a 30 second delay, 24 VAC is provided to terminals:
a) T2 on relite control which starts spark.
b) L on gas valve which opens pilot valve.
4. Pilot ignites:
a) Flame conduction stops spark from relite.
b) Mercury flame sensor opens main gas valve and pres¬
sure switch in gas valve holds pilot open.
5. After thermostat is satisfied, CR is deactivated:
a) CR2 opens turning off blower and pump.
b) CRl opens turning off gas flow.
6. As air flow from blower reduces pressure, switch changes to
normally closed position.
7. Boiler is now in "off" cycle.
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