Sheet 6843-1

air pressure drop across the burner in osi











540  780  1100 1590 

2450 3340  4570  230  8 



 920 1250 1830 



5600 7700* 230 8

Air rates are for burners operating on natural gas on ratio. Cold air capacity when not burning will be approximately 
7% greater.

6843-25 Hot Spot Burners are off ered in -3 and -4 sizes. 
These burners produce short, intense fl ames when operating 
on either natural gas or distillate oil. During oil fi ring, 8 psi of 
compressed air is required at the burner for atomization. During 
gas operation, 2 psi of compressed air is required to protect the 
atomizer, but 8 psi can be used if it is necessary to maintain the 
same burner capacity as during oil operation.

The 60% Alumina burner tiles withstand furnace temperatures to 
2800°F, and are grooved to provide a tight seal when mounted 
in either the furnace roof or wall. The tiles are reinforced with 
stainless steel needles, and require suitable hand protection be 
used during handling.

For natural gas operation, the pressure required at the gas 
connection is approximately one half the main air pressure at the 
air connection.

For oil operation, each burner must be equipped with an air/
oil Ratiotrol™ regulator and Sensitrol™ oil valve. This Sensitrol 
oil valve is not included with the burner assembly and must 
be ordered separately. As the atomizer nozzles are precision 
machined, a 100 mesh strainer must be installed in the oil line 
supplying the burners. In addition, to prevent damage, handling 
of the atomizers should be kept to a minimum. When shutting 
down the burners or switching over to gas operation, completely 
purge the oil atomizers of oil to prevent coking.

Standard burners are supplied with a fl angeless mounting plate 
for installation in a furnace roof. Optional fl anged mounting is 
available (at additional cost) for installation in a furnace wall. Add 
the letter "C" at the end of the burner designation when ordering 
the fl ange, i.e. 6843-3-25-C.

A 4011-12 pilot set is recommended for individual burner ignition. 
When multiple burners share a single pilot pre-mix header, a 
4021-12 pilot tip per burner with an appropriately sized air/gas 
mixer is recommended. A UV Detector should be used for fl ame 
supervision. While it is strongly recommended that the burners 
be lit at low fi re, the maximum main air pressure for lighting 
when fi ring oil is 8 osi.

The Dual-Fuel™ hot spot burners will perform well when coupled 
with an air/fuel ratio control system that is capable of controlling 
within the stability range of the burners. The extremely fast 
mixing characteristics of this burner limit excess air, and excess 
fuel should be limited to less than 10% Caution must be taken 
when calculating burner inputs. Due to expansion changes in the 
burner at diff erent fi ring rates, air fl ow dœ s not follow the square 
root law. In addition, burner air fl ow decreases as the furnace 
temperature increases, resulting in a change in air/fuel ratio. As 
a result, the fi nal burner air/fuel ratio settings must be made with 
the furnace at operating temperature. This results in the burners 
fi rings lightly lean during a cold start-up and reaching ratio as 
the furnace reaches temperature.


(for Btu/h HHV, multiply by 100)


 Gas only. 16 osi is maximum air rate for oil on 6843-4-25


North American Dual-Fuel


Hot Spot Burners


Situations dangerous to personnel and property may exist with the operation and maintenance of any combustion equipment. The presence of fuels, oxidants, hot and cold combustion products, hot 

surfaces, electrical power in control and ignition circuits, etc., are inherent with any combustion application. Components in combustion systems may exceed 160°F (71°C) surface temperatures and present hot 
surface contact hazard. Fives North American Combustion, Inc. suggests the use of combustion systems that are in compliance with all Safety Codes, Standards, Regulations and Directives; and care in operation.


Y | C


Catalog Combustion 2021 - Page 0827

Fives Group

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Fives Group Part Numbers on this Catalog Page
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1 6843-3-25 Fives Group Request Quote
2 6843-4-25 Fives Group Request Quote