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NORA Oilheat Technicians Manual

Chapter 5—Nozzles and Combustion Chambers 5-7 firing over 2 GPH. An interesting characteristic of solid cone patterns is that they become more and more hollow as flow rates increase, particularly above 8 GPH. In addition, increased pump pressure tends to make both hollow and solid patterns more hollow. Semi-solid: Many burners perform well with solid or hollow spray patterns. To accommodate these designs, nozzle manufacturers have developed patterns that are a compromise between solid and Figure 5-5: Manufacturers use different designations for their spray patterns hollow. We call these semi-solid patterns. Your job as a technician is to select the nozzle that puts the oil spray where the air velocity delivered by the burner is greatest. In most modern equipment, the appliance manufacturer designates the nozzle to use. Figure 5-5 describes the manufacturers’ different designations for their spray patterns. Spray angle Spray angle refers to the angle of the cone of spray from the nozzle. Spray angles are available from a 30-degree angle to a 90-degree angle to meet the wide variety of burner air patterns and chamber shapes. Generally, round or square chambers are fired with 70 to 90-degree nozzles. Short wide chambers need a short fat flame. Long narrow chambers usually require 30-degree to 70-degree solid cone nozzles. The spray pattern and angle must be such that all the droplets burn completely in suspension in the combustion area. Unburned oil must not strike (impinge) on any cold surface such as the chamber walls or floor, the crown sheet of the heat exchanger, or the burner end cone. Impingement of unburned drops will cause high smoke and will lead to future service calls. The correct spray pattern and angle depends on the air-oil mixing design of the burner and the shape of the combustion chamber. See Figures 5-6 and 5-7. Figure 5-6: Spray angles Figure 5-7: Spray angles based on chamber design Chapter 5 Nozzles and Chambers


NORA Oilheat Technicians Manual
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