Midco Unipower G-Series - Manual (Page 12)

IX Pilot and Flame Sensor
X Blower and Motor
CAUTION: Be sure that the Main Manual Shut-off, Manual Pilot Valve and Disconnect
Burner Switch are off before removing any parts for service.
CAUTION: Cover plates, guards and enclosures must be in place at all times except during
maintenance and service.
■ ■ The Unipower burner head is of the nozzle mixing (non-premix) flame retention type. This design
accommodates a high capacity without flame lift off and a low capacity without flash back.
■ ■ The burner box serves as an air plenum chamber and a frame to which all other parts are assembled.
Blower air enters the box and passes around the outside of the gas manifold and through the retention
plate. Gas passes through ports in the manifold, then through the retention plate where it is mixed with
the blower air by turbulence caused by the retention plate and into the combustion chamber for
burning. The gas ports are not adjustable. Variation in capacity is accomplished by a variation in gas
p r e s s u r e .
■ ■ Maintenance of the burner box and firing head is minimal, due to the simplicity of the parts and
absence of small air or gas passages. An occasional inspection of the parts in contact with the flame will
suffice. The flame retention plate must show no loss of metal or severe warping. If the heads of the
retention plate mounting screws show loss of metal they must be replaced. Use only stainless steel
s c r e w s .
Stainless nozzle sleeve must extend at least
1 / 2 " beyond flame retention plate.
■ ■ If the burner mounting flange or adjacent furnace wall show signs of overheating, check the
tightness of the burner mounting. The burner is intended to be sealed into the boiler opening both at
the face and at the mounting flange as shown in Figure 4, to prevent blow-back of hot flue products
around the nozzle and flange.
■ ■ The pilot is of the premix, blast type. Blower air is diverted from the blower housing through an air
orifice into the pilot mixing tee mounted on the burner back plate, where the proper amount of gas is
added through the pilot orifice. Both orifices are located at the end of their own respective tubes in
brass fittings leading into the mixing tee. The gas/air mixture is then discharged through the heat
resistant alloy flame retention pilot tip.
The spark rod is located on the center line of the pilot and is arranged to arc to the inside of
the central port. Spark current is supplied by a spark generator to ignite pilot gas.
■ ■ The pilot regulator is factory set for an outlet pressure of about 3 1 / 2 " W.C. for NATURAL gas and
PROPANE, which will be suitable for average conditions. Pressure can be varied to suit particular job
conditions. Do not increase orifice sizes indiscriminately. Pilot troubles may be introduced by causing the
pilot to float and lose contact with the flamerod or flame grounding area. Adjust the pilot per
paragraph 7 of Section VII Initial Start-Up.
■ ■ Service of the pilot will generally consist only of inspection and cleaning. Check that the pilot tip
ports, air tube and mixing tee are free of lint and dirt and that the pilot tip is free of corrosion. Make
sure that the air tube is re-inserted
into the blower housing pilot air tube
hole. The spark insulator and cable
must be clean, dray and free from
cracks and abrasions. Make spark
gap settings per Figure 14.
■ ■ Proper operation of the flame
safeguard depends on a reliable
current flow through the flamerod,
pilot flame and the flame grounding
area. The flamerod must be free of
any contact with conductive burner
parts. The insulator must be clean,
dry and free of cracks. While the rod
is made of heat resistant alloy, it may eventually deteriorate at the point of flame contact and should be
replaced if it is seriously corroded. See Figure 14 for the proper alignment of the flamerod. DO NOT
BEND FLAMEROD TO REDUCE THE DISTANCE FROM THE PILOT TIP.
■ ■ The blower functions to supply a constant and positive supply of air for complete combustion. Air
volume is controlled by an adjustable shutter in the blower outlet. A small supply of air is diverted ahead
of the shutter for the pilot and for operation of the blower air proving switch.
■ ■ No routine service is necessary on the blower other than an occasional cleaning the blower wheel. If
the blower wheel must be replaced, be sure to check the replacement for proper rotation. The concave
sides of the blades must face the blower outlet, and rotation of the wheel must be toward the outlet.
See Section VII Initial Start-Up, page 8 paragraph 6. Motor sizes and specifications are given in Table 1.
The
3 / 4 HP single phase motor used on the G69 burner uses a motor switching relay to handle the
motor load. All motors contain integral motor overload protection, usually manual, occasionally
automatic reset.
Part 2 Service
VIII Burner Box
and Firing Head
Burner Air
Approx.
Capacity
G56
G57
G58
G69
#26
(.147)
#30
(.128)
#26
(.147)
#26
(.147)
3500
3500
5000
5000
Table 5: Pilot Specifications
Natural
Pilot
Orifice
#60
(.040)
#60
(.040)
#55
(.052)
#55
(.052)
Propane
Pilot
Orifice
#64
(.036)
#64
(.036)
#56
(.046)
#56
(.046)
Wire Drill Sizes