Midco RS40 - Manual (Page 8)

DANGER: Be sure that the Main Manual Shut-Off Valve, Combination Valve and
Burner Power Switch are turned off before removing any parts for service.
WARNING: Do not attempt to FIRE the burner with the burner backplate removed
as air from the blower will not reach the combustion chamber and a dangerous level
of unburned gas could accumulate.
The nozzle and electrode assembly can be removed as a unit by disconnecting the field
installed union located between Combination Valve and Inlet piping and disconnecting
electrode leads. Withdraw nozzle assembly completely by removing the backplate.
?? Service will normally consist of inspection and cleaning. Check the electrodes for
deterioration and the insulators for cracks. The electrode assembly is adjustable, if
defective replace with a new one. Be sure to replace the rubber boot over the spark
electrode and treat electrode leads with care. Because of high voltage any damage to the
insulation is a potential leak path. When a new electrode is put in, be sure to set the spark
gap and flame sensor dimension, as shown in Figure 7.
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The blower assembly including the blower and motor, and motor mounting bracket can be
withdrawn as a unit after external wiring is disconnected.
?? Cleaning of the blower wheel is usually the only service required. Need for cleaning is
indicated if the air inlet of the burner housing show an accumulation of dust and lint, or if
the character of the flame—long, hazy and yellow (sooty)—indicates a deficiency of air.
Motor air cooling vents if present, should also be cleaned at this time.
?? If the motor must be replaced, remove the blower wheel first and remove the retainer
clips at the rubber motor grommets, pull the motor out of keyhole brackets. Remount in
reverse order, noting that brass flanges of rubber motor mounts are located against motor.
Do not omit the three clips. Position blower wheel on motor shaft to provide 1/8” inch
clearance between blower inlet opening and blower wheel ring.
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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 Combination Valve Gas Regulator has an outlet pressure setting range of 2.0" to
4.0" W.C. and is factory set for 2.0" W.C. Manifold Gas Pressure Tap is located on the
outlet end of the Combination Valve body.
?? If pressure adjustment is required for setting capacity, remove regulator cap for access
to slotted adjustment screw. Turning of adjustment screw counterclockwise reduces
pressure; clockwise increases pressure. Do not adjust past point where no change in
pressure is noted.
Note: Pressure setting can only be made with burner running and gas on.
CAUTION: If gas supply pressure is below its specified range during adjustment,
an overfire condition could result when 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.
XI Combination Gas Valve
8
X Blower Shelf Assembly
IX Nozzle and Electrodes
Figure 7: Nozzle Assembly and Electrode Assembly
Part 2 Service
Part 2 Service