Honeywell VR8204 Series Manual page 12

VR8204; VR4204
OPERATION
Opening is slowed because a flow restrictor in the
passage from the second automatic operator slows the rate
at which gas pressure is reduced under the second auto-
matic valve diaphragm after the second automatic operator
opens. Outlet pressure to the main burner increases gradu-
ally from 0 in. wc [0 kPa] to rated output pressure within 3-
6 seconds (for an 80,000 Btuh furnace at 7 in. wc [1.8 kPa]
inlet pressure and 3.5 in. wc [0.9 kPa] outlet pressure).
STEP-OPENING REGULATION
Step-opening gas controls actually combine two pres-
sure regulators, one for the low pressure and one for the
full-rate pressure. When the thermostat calls for heat, the
automatic operator valve disc opens. The low pressure
regulator maintains outlet pressure at the preset step rate for
several seconds. Then the regulator valve is forced fully
open by the timing diaphragm, which is operated by bleed
Fig. 12—Position of gas control components during thermostat off cycle.
GAS
CONTROL
INLET
NOTE: SECOND AUTOMATIC VALVE OPERATOR AND
SERVO PRESSURE REGULATOR SHOWN OUTSIDE
GAS CONTROL FOR EASE IN TRACING GAS FLOW.
68-0047—2
CONTROL
KNOB
FIRST
AUTOMATIC
VALVE
SOLENOID
FIRST AUTOMATIC VALVE
SLOW-OPENING GAS CONTROL HAS A GAS FLOW RESTRICTOR IN THIS PASSAGE.
1
gas. When the low pressure regulator is fully open, the high
pressure regulator maintains the desired full-rate outlet
pressure as described for the standard regulator.
The step model requires approximately 60 seconds to
reset once the main burner goes off. If it is re-energized
within 60 seconds, it may bypass or shorten the length of
the low pressure step. The burner may relight at the full
flow rate.
WHEN THE CALL FOR HEAT ENDS
When the call for heat ends, the first automatic valve and
the second automatic valve operator close, bypassing the
regulator(s) and shutting off the main burner and the pilot.
As pressure inside the gas control and underneath the
automatic valve diaphragm equalizes, spring pressure closes
the second automatic valve to provide a second barrier to
gas flow.
SECOND AUTOMATIC
VALVE OPERATOR
1
SECOND AUTOMATIC
VALVE DIAPHRAGM
12
SECOND
AUTOMATIC
OPERATOR
SOLENOID
SERVO PRESSURE
REGULATOR
SECOND
AUTOMATIC
OPERATOR
VALVE DISC
PILOT
GAS
OUTLET
GAS
CONTROL
OUTLET
M9126