STARTUP AND CHECKOUT • MAINTENANCE • OPERATION
TABLE 4B—PRESSURE REGULATOR SPECIFICATION PRESSURES (kPa).
Regular preventive maintenance is important in applica-
tions that place a heavy load on system controls, such as in
the commercial cooking and agricultural and industrial
• In many such applications, particularly commercial
cooking, the equipment operates 100,000-200,000
cycles per year. Such heavy cycling can wear out the
gas control in one to two years.
• Exposure to water, dirt, chemicals and heat can dam-
age the gas control and shut down the control system.
The maintenance program should include regular check-
out of the control; see Startup and Checkout section, and
regular checkout of the control system; see the appliance
Maintenance frequency must be determined individu-
ally for each application. Some considerations are:
• Cycling frequency. Appliances that may cycle 20,000
times annually should be checked monthly.
• Intermittent use. Appliances that are used seasonally
should be checked before shutdown and again before
the next use.
The VR8204/VR4204 gas controls provide ON-OFF
manual control of gas flow. In the OFF position, gas flow to
both pilot and main burners is mechanically blocked. In the
ON position, gas flows to the pilot burner and the main
burner under control of the thermostat, the intermittent
pilot (IP) module, and the two automatic main valves.
SYSTEM OPERATION WITH MODULE
When the thermostat calls for heat, the IP module is
energized. The IP module, in turn, activates the first auto-
matic valve of the gas control. Pilot gas is allowed to flow
through the control to the pilot burner. Simultaneously, the
IP module generates a spark at the igniter-sensor and lights
the pilot. The pilot flame is sensed by the igniter-sensor,
and spark generation ends.
After the pilot is lit, the IP module energizes the solenoid
for the second automatic valve operator and gas flows to the
main burner (the first automatic valve remains energized).
The second automatic valve diaphragm, controlled by the
1.2 - 1.7
2.9 - 3.9
1.2 - 1.7
2.9 - 3.9
Nominal Outlet Pressure
• Consequence of unexpected shutdown. Where the
cost of an unexpected shutdown would be high, the
system should be checked more often.
• Dusty, wet, or corrosive environment. Since these
environments can cause the gas control to deteriorate
more rapidly, the system should be checked more
Gas valves exposed to high ammonia conditions; i.e.,
those used in greenhouses or animal barns, may fail in one
or two years. Contact your Honeywell sales representative
to request a gas valve with corrosion resistant construction.
The system should be replaced if:
• It does not perform properly on checkout or trouble-
• The gas control knob is hard to turn.
• The gas control is likely to have operated for more
than 200,000 cycles.
servo pressure regulator, opens and adjusts gas flow as long
as the system is powered and the pilot is burning. The servo
pressure regulator monitors outlet pressure to provide an
even flow of gas to the main burner. Loss of power (ther-
mostat satisfied) de-energizes the IP module and closes
both automatic valves. The system is ready to return to
normal service when power is restored through the thermo-
Loss of pilot flame, or flame too small to reliably light
main burner, closes the second automatic valve operator.
The IP module then attempts to restart pilot. On IP modules
with lockout timers, the first automatic valve closes after
the lockout period. On IP modules without lockout timers,
the trial for ignition continues indefinitely and the first
automatic valve remains open.
If pilot flame is restarted successfully, main burner is
reopened, and gas flows to main burner as described above.
Gas control operation is described in more detail below.
0.7 - 1.2
2.0 - 3.0
0.7 - 1.2
2.0 - 3.0