68-0046—4
14
VR8200, VR4200
OPERATION
Fig. 15—Position of gas control components during the thermostat on cycle.
SAFETY SHUTOFF OPERATION
In the safety shutoff position, pilot and main burner gas
flow is permitted.
Safety shutoff occurs:
• When the gas control knob is manually turned to OFF.
• When the pilot goes out or becomes too small to
sus-tain normal ignition.
Gas Control Knob Turned to OFF
When the gas control knob is turned to OFF, it pulls up
and locks the reset button and closes the first automatic
valve. The small valve seat attached to the reset button
closes and shuts off pilot gas flow. When the pilot goes out,
thermocouple current drops and the power unit drops out,
closing the safety shutoff valve. This shuts off pilot and
main burner gas flow. With the loss of outlet pressure, the
second automatic valve closes and is held closed by spring
pressure on the diaphrahm.
When Pilot Flame Goes Out
When pilot flame goes out or is too small to reliably light
the main burner, thermocouple output drops below the
power unit hold-in valve. The power unit drops out, closing
the safety valve and stopping all gas flow through the con-
trol. With the loss of outlet pressure, the second automatic
valve closes and is held closed by spring pressure on the
diaphragm.
FIRST
AUTOMATIC
VALVE
SOLENOID
GAS
CONTROL KNOB
GAS
CONTROL
INLET
SAFETY
SHUTOFF VALVE
RESET BUTTON
VALVE DISC
POWER UNIT
SECOND
AUTOMATIC VALVE
OPERATOR
SECOND
AUTOMATIC
OPERATOR
SOLENOID
SECOND
AUTOMATIC
OPERATOR
VALVE DISC
SERVO
PRESSURE
REGULATOR
GAS
CONTROL
OUTLET
SECOND AUTOMATIC
VALVE DIAPHRAGM
FIRST
AUTOMATIC
VALVE
M6919
1
1
PILOT
GAS
OUTLET
NOTE: SECOND AUTOMATIC VALVE OPERATOR AND
SERVO PRESSURE REGULATOR SHOWN OUTSIDE OF
GAS CONTROL FOR EASE IN TRACING GAS FLOW.
SLOW-OPENING GAS CONTROL HAS A GAS
FLOW RESTRICTOR IN THIS PASSAGE.
RED RESET
BUTTON