The V800 combination gas control family provides
position (OFF-PILOT-ON) manual control of gas flow. In
Fig. 14, the gas control knob is in the ON position, the
pilot is proven by the thermocouple/generator, and the
thermostat is calling for heat.
GAS CONTROL KNOB AT OFF
The manual safety shutoff valve and main valve are
closed. No gas flows into the control.
GAS CONTROL KNOB AT PILOT
The manual safety shutoff valve and main valve are
closed until the gas control knob is manually depressed,
When depressed, the manual safety shutoff valve is
opened, allowing pilot gas flow so the pilot can be lit. After
about one minute, the thermocouple/generator current is
enough so the power unit and holds the manual shutoff
valve open. The main valve remains closed and prevents
main burner gas flow until the thermostat calls for heat.
GAS CONTROL KNOB AT ON;
NO CALL FOR HEAT
This is the standby position. The safety shutoff valve is
open, but the main valve is closed. Gas flow is restricted
to the pilot only.
GAS CONTROL KNOB AT ON;
THERMOSTAT CALLS FOR HEAT
On a call for heat, the valve operator opens the
hand port and closes the right-hand port. Gas flows
through the working gas channel, increasing the working
gas pressure. The increased pressure pushes against
the main valve diaphragm, opening the main valve and
permitting gas flow through the control to the main burner.
The servo pressure regulator controls outlet gas pressure
to the main burner.
GAS CONTROL KNOB AT OFF;
THERMOSTAT ENDS CALL FOR HEAT
When a call for heat ends, the valve operator closes
the left-hand port and opens the right-hand port, Gas flow
through the working gas channel is reversed, decreasing
the working gas pressure. The decreased pressure al-
lows the main valve diaphragm to retract and close the
main valve. The working gas flows through the evacu-
ation channel to the gas outlet to the main burner. The
safety valve remains open, allowing pilot gas flow.
LOSS OF PILOT FLAME
The
safety shutoff mechanism shuts down
the combination gas control if the pilot flame becomes
extinguished or too small for satisfactory burner ignition.
As the pilot burns, it constantly heats the thermo-
couple or Powerpile generator, providing current for the
Pilotstat power unit in the gas control. A properly burning
pilot supplies the power unit with enough current to keep
the safety valve open and allow pilot gas flow. If the pilot
goes out or decreases current to the power unit, the
power unit will “drop out,” closing the safety valve and
preventing pilot gas flow and main burner gas flow. To
restart the system, the pilot flame must be manually relit
and the Pilotstat must be manually reset.
The VS820 and VS821 Powerpile models generate
current independent of the line voltage and continue
regulating pilot and main burner gas flow. Therefore, in a
power outage, the gas control continues operating.
SERVO PRESSURE REGULATORS
When the pilot flame is burning properly and the th-
ermostat calls for heat, the servo pressure regulator
senses and varies the outlet pressure to the main burner.
When the thermostat calls for heat, the valve operator
ON-OFF lever opens the left-hand gas supply port, lifting
the servo regulator valve off it’s seat and allowing gas
flow into the working gas channel and evacuation chan-
nel. The working gas channel gas flow increases the
pressure in the working gas pressure chamber which
raises the main valve diaphragm and lifts the main valve
off it’s seat, allowing main burner gas flow.
Outlet gas pressure variations are instantly reflected
through the evacuation channel to reposition the servo
regulator diaphragm. Repositioning the diaphragm ad-
justs the
pressure by altering the flow rate through
the servo regulator valve.
When the outlet pressure rises, the servo regulator
valve opens and allows more evacuation channel gas
flow. This decreases the pressure in the working gas
pressure chamber and lowers the main valve toward its
seat, lowering the outlet pressure.
The opposite occurs when the outlet pressure falls.
The servo regulator valve closes and allows less evacu-
ation gas channel gas flow. This increases the pressure
in the working gas pressure chamber and raises the main
valve from its seat, raising outlet pressure.
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