Midco 400B-33 - Manual (Page 8)

FIGURE 7 General Assembly
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XI REDUNDANT COMBINATION GAS
VALVE
The 24 volt Combination Valve serves three functions:
1.) Manual Gas Shut-Off, 2.) Manifold gas pressure
regulation, 3.) Automatic electric redundant (double
seated) gas valve.
■ ■ For manual control the Manual Gas Cock Knob is
turned full ON or full OFF. The dial has to be depressed
to be turned in one direction, but it depends on the make
of the valve whether it is to the ON or OFF position.
■ ■ The Main Gas Pressure Regulator, which has an outlet
pressure setting range of approximately 2.0" to 4.0"
W.C., is factory set for a manifold gas pressure of 3.5"
W.C. for NATURAL. If pressure adjustment is required
for setting capacity, remove regulator cap for access to
slotted adjustment screw. Turning of adjustment screw
counter-clockwise reduces pressure; clockwise
increases pressure.Do not adjust past the point where no
change in pressure is noted.
NOTE: Pressure setting must be made with burner
running and main gas ON.
CAUTION: When adjusting the regulator, if gas
supply pressure is below its specified range, an
overfire condition could result as pressure returns to
normal, particularly if the regulator adjustment
screw is bottomed out.
ALWAYS confirm that at least the minimum rated gas
pressure is being supplied to the burner during regulator
adjustments, and NEVER bottom out regulator screw.
■ ■ To set to low outlet pressure for initial start-up, turn the
adjusting screw counter-clockwise 2.5 turns to raise it to
about 1/4" below the top.
■ ■ The tap for manifold gas pressure measurement is
located in the burner spud holder (see Figure 7).
Remove plug for access.
■ ■ If the Main Gas Pressure Regulator fails to maintain a
constant manifold gas pressure within ±0.1" W.C., and it
is confirmed that the inlet gas pressure to the
combination valve is 14.0" W.C. maximum during
standby, and 5.0" W.C. minimum for NATURAL gas
(11.0" W.C. for PROPANE gas), with the main flame on,
the regulator portion of the valve is defective and the
entire valve must be replaced.
■ ■ If, on a call for heat, flame ignition does not occur, refer
to the TROUBLE CHART for further information.
■ ■ If leakage through the valve occurs, as evidenced by
the presence of flame on standby, the entire valve must
be replaced.
■ ■ If the Combination Valve has been moved or replaced,
soap bubble test for leaks with the burner running.
XII S8680J ELECTRONIC CONTROL
■ ■ For operation characteristics refer to Honeywell
Control literature provided with burner.
XIII SPECIAL EQUIPMENT (OEM
VERSIONS)
Special equipment, either factory or contractor
installed, may cause variation in the procedures and
descriptions given in this manual.
Consult the OEM's manual to identify the differences in
the information.