Midco A50G Service Manual

Installation and Service Instructions

Midco International Inc.

4140 West Victoria Street Chicago, Illinois 60646
tel [phone] fax [phone] web www.midco-intl.com

199

8449-11

Printed in U.S.A.

In the United States, installation must conform with local codes or

in the absence of local codes, with the National Fuel Gas
Code, ANSI Z223.1-latest edition available from American
National Standard Institute. Further reference should be made to
the recommendation of your fuel supplier.

In Canada, installation must conform with local codes or in the

absence of local codes, with Installation Codes for Gas

Burning Appliances and Equipment, CGA Standard
CAN/CGA 1-B-149.1 or 2. When the conversion burner is used

on a Forced Air Central Furnace, the two yellow and black
warning labels in the literature envelope shall be attached in
accordance with Installation Code, CGA Standard CAN/CGA
1-B149, Clause 5.4.4.4. Further reference should be made to
the recommendation of your fuel supplier.

WARNING: Additions, changes, conversions and service
must be performed by an authorized Midco
representative, service agency or the fuel supplier. Use
only MIDCO specified and approved parts.

INSTALLER:

Inform and demonstrate to the user the
correct operation and maintenance of the gas
utilization equipment. Inform the user of the hazards
of storing flammable liquids and vapors in the
vicinity of this gas utilization equipment and remove
such hazards. Affix this manual and associated
literature to the conversion burner.

CODE COMPLIANCE IS THE SOLE RESPONSIBILITY OF THE
INSTALLER.

USER:

Retain this manual for future reference. If other
than routine service or maintenance as described in this
manual and associated literature is required, contact a
qualified service agency. DO NOT ATTEMPT REPAIRS.
An inadvertent service error could result in a
dangerous condition.

Unipower A-Series

Gas Burners

BURNER
MODEL

BILL OF MAT'L
NUMBER

DATE CODE

WIRING DIAGRAM

PIPING DIAGRAM

START-UP INSTRUCTIONS

FOR SERVICE CONTACT:

name

address

phone

SSAAFFEETTYY IINNFFOORRMMAATTIIOONN TTEERRMMSS:: The following terms are used to identify hazards, safety precautions or special notations

and have standard meanings throughout this manual. When you see the safety alert symbol and one of the safety
information terms as shown below, be aware of the hazard potential.

WARNING: Signifies a hazard that could result in personal injury or death.
CAUTION: Identifies unsafe practices which would result in minor personal injury or product and property damage.

Warning: If the information in these instructions
is not followed exactly, a fire or explosion may result,
causing property damage, personal injury or death.

Do not store or use gasoline or other
flammable vapors and liquids in the

vicinity of this or any other appliance.

WHAT TO DO IF YOU SMELL GAS

• Do not try to light any appliance.

• Do not touch any electrical switch;
do not use any phone in the building.

• Immediately call your gas supplier from
another building's phone. Follow the gas
supplier's instructions.

• If you cannot reach your gas supplier,
call the fire department.

Part 1 Installation

I Specifications

Burner Style Power Type
Flame Safeguard Instantaneous electronic type

with flamerod detection (flame rectification).

• Provides pre-purge and intermittent pilot operation on UL listed models up to 2500 MBH
maximum input.

• Provides pre-purge and interrupted pilot operation on UL listed models over 2500 MBH
max.

Pilot Spark Ignited
Fuel Natural or Propane Gas to 14" W.C. Pressure
Controls 120 Volt, 60 Hz., 1-Phase
Burner Capacity Chart page 12
In U.S.A.: UL Listed, In Canada: ULC (A5 Series only)

Burner

Model

Minimum***

Maximum H.P. PhaseVolts

Burner Input Capacity*

Natural or Propane Gas MBH**

Motors

3450 RPM. 60 Hz.

A50G
A52G
A53G
A55G
A73G
A75G
A77G

1
1
1
1
3
3
3

1

/

3

1

/

2

3

/

4

3

/

4

11/

2

2

2

115

115
115/230
115/230
230/460
230/460
230/460

420
840
840

840
1,680
1,680
1,680

1,500
2,000
2,500
3,000
4,200
5,000
6,000

Table 1: Burner Specifications

* Values given based on -0.1" W.C. to +0.1" W.C. firebox pressure, altitudes to

2,000 feet. Derate burner for altitudes over 2,000 feet by 4% for each 1,000

feet over sea level. (One gallon fuel oil=140 MBH).
** Refer to Burner Spec Plate for Inlet and Manifold gas pressure required.
*** Modulating and High-Low-Off burners are limited to a 3 to 1 turndown

ratio.

All models are capable of full input start. However, in some cases, (i.e. restricted draft or induced
draft) optional low fire start may be necessary. Specify On-Off, Hi-Lo-Off or Full Mod as required.

■■

■■ A permanent means must be provided to supply an ample volume of fresh air for combustion

and boiler room ventilation. A direct opening to the outside air for combustion and boiler room
ventilation. A direct opening to the outside air should be provided sized on the basis of

1

/2square

foot of free opening for each 1,000 MBH of burner input when the flue pipe is equipped with a
barometric draft control, as is commonly used on burners of this size. If the ventilation opening is

screened, it should be of 1

1

/4" mesh. The opening should be located at least six feet over ground

level to prevent accidental obstruction. If a direct opening to the outside air is not available, an
amply sized air duct can be run to the nearest outside air source.

■■

■■ While the Unipower A Series burner will perform successfully under moderate or momentary

back draft conditions, it is not intended for operation under sustained reverse draft, as might be
encountered in building with large ventilating fans but with insufficient make-up air. Even if
burner operation is successful under these conditions, they must be corrected to prevent the
hazard of drawing flue gases into the building.

■■

■■ The entire heating system should be inspected, cleaned and repaired as necessary to provide

proper heating.

■■

■■ Remove all grates and obstructions from the firebox, clean thoroughly, and seal all joints and

cracks. Complete sealing of the firebox is required where the combustion chamber pressure will
be positive during burner operation. It is also beneficial where the pressure is negative as it
promotes combustion efficiency.

■■

■■ Firing door catches should be filed off or otherwise arranged so that the door will open easily

to relieve excess pressure. No positive catches should be used. The use of a spring-type door
holder is recommended.

■■

■■ If the appliance has been designed for automatic firing and contains no firing doors, an

observation port should be provided that will allow inspection of the main flame and pilot.

II Ventilation

III Preparation of the

Heating Appliance

2

III Preparation of the

Heating Appliance

Continued

IV Combustion Chamber

■■

■■ Make sure that the boiler gauge glass is clean so that water level can be easily ascertained. The

pop safety valve should be checked to see that it is in good operating condition. If an existing low
water cut-off is to be used, make sure it is clean and functioning properly.

■■

■■ The Unipower gas burner is designed for "in-shot" firing. It can be fired into the ashpit of a

boiler designed for solid fuels, or it can be fired into the primary heat exchanger of a boiler or
warm-air furnace designed for liquid or gaseous fuels. The ashpit installation requires a refractory
lining.

■■

■■ For conventional firebox boilers refer to Table 2 and Figure 1 for recommended combustion

chamber dimension and typical floor and wall construction. If the recommended dimensions
cannot be provided, make length as long as possible and increase the width to maintain the floor
area. Where the floor are must be reduced, use the optional construction shown in Figures 2 or 3.

Figure 1: Typical Floor and Wall Construction

Standard Size Combustion Chamber up to 225 MBH per square foot

Figure 2: Typical Floor and Wall Construction

Alternate Size Combustion Chamber up to 275 MBH per square foot

Figure 3: Typical Floor and Wall Construction

Alternate Size Combustion Chamber up to 350 MBH per square foot (Maximum)

3

■■

■■ For warm-air furnaces or Scotch Marine boilers with tubular combustion chambers, the

combustion chamber length must be great enough to exceed the lengths given in Table 2 by at
least 20%.

■■

■■ Combustion chamber proportions may be changed if necessary to avoid flame impingement on

critical parts such as drop sections in cast iron boilers or the heat exchanger surfaces of a warm­air furnace. If sustained flame contact cannot be avoided, protect the surfaces with 2

1

/2" or

firebrick.

■■

■■ The burner nozzle must not extend into the combustion chamber. It should be sealed into the

opening as shown in Figure 4. The burner mounting to the appliance front must be rigid and
sealed with

1

/4" soft refractory sheet or rope. See Figure 5 for mounting flange dimensions.

■■

■■ Allow a space of about 1" between the edges of the floor brickwork and the appliance base to

allow for expansion and creep. Where wall construction is such that both ends butt against rigid
appliance parts such as the base of a water leg, allow

1

/4" space between bricks every four feet

or so for expansion joints, particularly when reduced size combustion chambers are used.

Firing Door Installations

■■

■■ Greater care in planning will be required for firing door applications since flame impingement

on heat exchange surfaces is more probable. Do not fire a boiler containing a drop section
directly in the path of the flame, or over the water grate in a smokeless type boiler. The firebox
length must be great enough to exceed the combustion chamber lengths given in Table 2 by at
least 20%.

■■

■■ When raising the floor, maintain sufficient firebox volume to limit the heat release per cubic

foot to 50 MBH or less. Use the entire floor as a combustion chamber and cover any water leg
base to 6" from the bottom to avoid firing areas filled with sediment. Floor construction should
conform to Figures 1, 2 or 3.

■■

■■ The burner mounting in the door must be rigid and refractory lined as shown in Figure 9. The

burner nozzle must not protrude directly into the combustion chamber. The refractory liner must
be flush with or extend beyond the burner face as shown in Figure 4. A sheet metal rim should
encase the refractory up to the inside of the boiler wall. It should be intermittently bent inward to
retain the refractory or other means of anchoring should be provided. A refractory felt blanket
can be used in lieu of castable refractory, which will simplify construction at the burner entry.

IV Combustion Chamber

Continued

Figure 4: Construction at Burner Entrance

4

C
L