Honeywell VR8204 Series Manual page 11

VALVE POSITION DURING THERMOSTAT OFF
CYCLE
The valve is positioned as shown in Fig. 13 when the:
• manual gas control knob is in the ON position.
• thermostat is not calling for heat.
The first automatic valve is closed. The second auto-
matic valve operator is de-energized, closing the channel to
the pressure regulator, and opening a channel to the under-
side of the second automatic valve diaphragm. The combi-
nation of spring pressure under the second automatic valve
diaphragm and lack of outlet pressure hold the diaphragm
firmly closed. Gas flow to the pilot burner is blocked by the
first automatic valve and gas flow to the main burner is
blocked by both valves.
WHEN THERMOSTAT CALLS FOR HEAT
When the thermostat calls for heat, the trial for pilot
ignition begins. The first automatic valve solenoid is ener-
gized by the module and opens, allowing gas to flow to the
pilot burner. Gas also flows to the second automatic valve
operator, but is mechanically blocked at the operator. See
Fig. 11.
After the pilot lights and the pilot flame is sensed by the
igniter-sensor, the second automatic valve solenoid is ener-
gized by the module, and the second automatic operator
valve disc is lifted from its seat. See Fig. 12. This diverts
gas flow from the second automatic valve diaphragm and
causes a reduction of pressure on the underside of this
diaphragm. The reduced pressure on the bottom of the
automatic valve diaphragm repositions the diaphragm down-
Fig. 11—Position of gas control components during the trial for pilot ignition.
GAS
CONTROL
INLET
FIRST AUTOMATIC VALVE
NOTE: SECOND AUTOMATIC VALVE OPERATOR AND
SERVO PRESSURE REGULATOR SHOWN OUTSIDE
GAS CONTROL FOR EASE IN TRACING GAS FLOW.
CONTROL
KNOB
FIRST
AUTOMATIC
VALVE
SOLENOID
SECOND AUTOMATIC
VALVE DIAPHRAGM
1 SLOW-OPENING GAS CONTROL HAS A GAS FLOW RESTRICTOR IN THIS PASSAGE.
ward, away from the valve seat, allowing gas to flow to the
main burner.
STANDARD REGULATION
During the ON cycle, the servo pressure regulator pro-
vides close control of outlet pressure, even if inlet pressure
and flow rate vary widely. Any outlet pressure change is
immediately reflected back to the pressure regulator dia-
phragm, which repositions to change the flow rate through
the regulator valve, and thus through the automatic valve.
If outlet pressure begins to rise, the pressure regulator
diaphragm moves slightly higher, allowing less gas flow to
the gas control outlet. This increases gas pressure under the
automatic valve diaphragm and repositions the valve disc
closer to the seat. Thus, flow of gas through the second
automatic valve is reduced, and outlet pressure falls to the
desired level.
If outlet pressure begins to fall, the pressure regulator
diaphragm moves slightly lower, allowing more gas flow to
the gas control outlet. This decreases gas pressure under the
second automatic valve diaphragm and repositions the
valve disc further from the seat. Thus, flow of gas through
the second automatic valve is increased, and outlet pressure
rises to the desired level.
SLOW-OPENING REGULATION
Slow-opening gas controls function the same as stan-
dard models except that when the thermostat calls for heat,
the second automatic valve opens gradually.
SECOND AUTOMATIC SECOND
VALVE OPERATOR AUTOMATIC
OPERATOR
SOLENOID
SECOND
AUTOMATIC
OPERATOR
VALVE DISC
1
11
VR8204; VR4204
OPERATION
SERVO PRESSURE
REGULATOR
PILOT
GAS
OUTLET
GAS
CONTROL
OUTLET
M9127
68-0047—2