burners atomize the oil by fuel-oil pressure. The fuel-oil system of a pressure-atomizing burner consists of a strainer, pump, pressure-regulating valve, shutoff valve, and atomizing nozzle (fig. 4-39). The nozzle and electrode assembly includes the oil pipe, nozzle holder, nozzle, strainer, electrode insulators, electrodes, supporting clamp for all parts, and static disk. The oil pipe is a steel rod with a fine hole drilled through it. This hole reduces oil storage in the nozzle to a minimum that prevents squirting at the nozzle when the burner shuts off.

The air system consists of a power-driven blower with means to throttle the air inlet, an air tube that surrounds the nozzle and electrode assembly, and vanes or other means to provide turbulence for proper mixing of the air and oil. The blower and oil pump are generally connected by a flexible coupling to the burner motor. Atomizing nozzles can be furnished to suit both the angle of spray and the oil rate of a particular installation. Flame shape can also be varied by changing the design of the air exit at the end of the air tubes. Oil pressures are usually about 100 psi, but pressures considerably greater are sometimes used.

Electric ignition is almost exclusively used. Electrodes are located near the nozzle but must not be in the path of the fuel oil spray. The step-up tran sform er provides the high voltage (usually 10,000 the electrode tips. volts) necessary to make an intense spark jump across

Figure 4-37. - Cutaway view of a typical oil-fired furnace.

Figure 4-38. - Oil-fired floor furnace.