Honeywell VR8305 Quick Manual Download Page 11

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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 diaphragm, 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 Pressure Regulation (VR8305H)

Slow-opening gas controls function the same as standard

models except that when the thermostat calls for heat, the
second automatic valve opens gradually. 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 automatic valve diaphragm after
the second automatic operator opens. Outlet pressure to the

main burner increases gradually from 0 inches wc [0 kPa] to
rated output pressure within 3-6 seconds (for an 80,000 Btuh
furnace at 7 inches wc [1.8 kPa] inlet pressure and 3.5 inches
wc [0.9 kPa] outlet pressure).

Step-Opening Pressure Regulation (VR8305P)

Step-opening gas controls actually combine two pressure

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 main-
tains 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 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. As pressure
inside the gas control and beneath the automatic valve dia-
phragm equalizes, spring pressure closes the second auto-
matic valve to provide a second barrier to gas flow.

Fig. 10—Position of gas control components during thermostat off cycle.

VR8305

OPERATION

68-0109—3

FIRST
AUTOMATIC
VALVE
SOLENOID

CONTROL
KNOB

GAS
CONTROL
INLET

SECOND AUTOMATIC
VALVE OPERATOR

SECOND
AUTOMATIC
OPERATOR
SOLENOID

SECOND
AUTOMATIC
OPERATOR
VALVE DISC

SERVO PRESSURE
REGULATOR

GAS
CONTROL
OUTLET