Midco F400-33 - Manual (Page 7)

After the initial start-up procedure, the following steps
can be followed for routine start-up and shut-down on a
seasonal or extended basis.
BURNER START UP
1. Make sure burner power switch is off.
2. Set controller to call for heat.
3. Open firing door.
4. Open Main and Pilot Manual Shut-Off Valves.
5. Reset flame safeguard.
6. Turn on burner power switch.
7. Close firing door after main flame ignites.
8. Reset controller to desired setting.
BURNER SHUT DOWN
1. Turn off burner power switch.
2. Close Main Manual Shut-Off Valves.
3. Close pilot manual Shut-Off Valves.
PART 2 SERVICE
DANGER: Do not tamper with the unit or con-
trols. If trouble occurs contact the installing con-
tractor, service agency, or fuel supplier. See front
cover.
WARNING: Be sure that the main and pilot
manual Shut-Off Valves are closed and the burner
power supply is turned off before removing any
parts for service.
CAUTION: Cover plates, guards, and enclosures
must be maintained in place at all times except dur-
ing maintenance and service.
IX PILOT
The pilot is of the premix, blast type. The full force of
blower air is brought into the mixing tube where the prop-
er amount of gas is added through the pilot orifice. This
mixture is discharged through the pilot which contains a
perforated flame retention plate. The outer holes di-
verge to spray the mixture against the side wall of the pi-
lot tip to provide flame retention. The mixture through
the center port provides the flame that contacts the
flame detection rod and also ignites the main gas.
■ Surrounding the base of the pilot flame is a conical
shroud which protects the flame against extraneous air
currents and inhibits "blow-off" from an overly rich flame.
TABLE 4: Pilot Specifications
CAUTION: Do not indiscriminately increase pilot
orifice size. Pilot troubles are rarely cured in this
manner and new troubles may be created.
■ The pilot gas orifice is the same size for both natural
and propane gas, consequently the gas pressure re-
quired for propane is lower than that required for natural
gas. Under normal conditions, with a slight negative
pressure in the combustion chamber, pilot operating
MODEL
400-33
F400-33
-7-
ORIFICE
DIAMETER
DRILL #68
.031 DIA.
DRILL #55
.052 DIA.
NOMINAL BTU/Cu. Ft. Hr.
NATURAL 1000ÑPROPANE 2500
APPROX.
CAPACITY
BTU/Hr.
2500
7000
PILOT GAS PRESSURE
NATURAL
2.5"-4.0"W.C.
PROPANE
2.25"-3.5"W.C
pressures are 3.5"W.C. NATURAL gas and 2.25"W.C.
PROPANE.
■ Some conditions which may require a change from
the normal setting include: extremely long tubing con-
nections between the regulator and pilot solenoid, high
negative or positive combustion chamber pressure, actu-
al air shutter setting and altitude extremes.
■ Do not subject the pilot to an inlet pressure over
14.0"W.C. See section VI PIPING for high pressure gas.
Note that the standard pilot pressure regulator is not a
tight shut-off and, during standby, the outlet pressure will
build up to the full inlet pressure.
■ The spark rod is located on the center line of the pilot
and is positioned so the high tension voltage will arc to
the inside of the center port of the retention plate (see
Figure 7).
■ The flame rod must be positioned as shown in Figure
7 so that the flame safeguard will detect a proper flame.
Note that it is slightly above the centerline of the pilot.
■ Both the spark and flame rods are currently carrying
conductors and, along with their connecting wires, must
be kept free of contact with conductive metal parts of the
burner. Rod insulators and wire insulator should be
clean, dry and free of cracks.
■ Rods are made from heat resistant alloys and can be
expected to have a long service life. They should be rou-
tinely inspected, however, for corrosion or loss of metal.
■ The pilot air tube must be kept free of kinks or inside
obstructions and its inlet end must be positioned per Fig-
ure 7, otherwise air flow could be reduced and adverse-
ly affect the pilot flame.
X MOTOR, BLOWER INTERLOCK &
CENTRIFUGAL ACTUATOR
CAUTION: BEFORE SERVICING, mark with a
scribe line or measure position of combustion air
controlling shutter, so that it can be reset to its origi-
nal position following servicing.
The blower, which is driven by the motor, functions to
supply a constant and dependable source of combustion
air. A centrifugal actuator is mounted on the blower
wheel and, through the interlock switch, proves blower
operation on every run.
■ Cleaning of the blower wheel is usually the only ser-
vice required. Need for cleaning is indicated if the air
cage assembly shows an accumulation of dust and lint,
or if the character of the flame indicates a deficiency of
air. Motor cooling air vents if present should also be
cleaned at this time.
■ The blower side plate, motor and wheel are removed
as an assembly. Disconnect the motor wires, and con-
duit then remove the side plate screws.
■ Unless the blower wheel location has been disturbed,
a replacement switch and bracket assembly will assume
the correct position when mounted. Confirmation of the
correct assembly can be made by measurement and
test.
■ A) With the switch assembly unmounted, insert a
probe through the blower opening and push actuator
disk inward as far as it will go. Mark the depth of inser-
tion on the probe and measure. Measure the portion of
the switch plunger (unrestrained) protruding past the
bracket arms. The probe insertion measurement should
exceed the switch stem protrusion by at least
1 Ъ 16 ".