spring located behind the piston. When the fuel pump gears develop sufficient pressure to overcome the spring tension, the piston is forced back, allowing oil to flow through the nozzle discharge port. The pressure adjusting screw regulates the spring tension controlling the pressure of the oil discharged to the nozzle. • The strainer screen, see Figure 4-3, within the fuel unit reservoir, filters the incoming oil and helps to prevent any contamination from entering the nozzle. • A solid shaft extending through the pump housing seal drives the gear pump. The end of this shaft is connected to the burner motor by a flexible coupling. (Note that the Pressure Gauge Port Nozzle Port 4-4 Fuel Units and Oil Valves R.P.M. rating of the gear pump must be the same as the burner motor.) • A shaft seal is provided to prevent oil from leaking out of the fuel pump housing around the rotating shaft. Lubrication is provided to this seal through internal porting. Operation of the single stage fuel unit The single stage fuel pump, Figure 4-4, produces both pressure and vacuum. Pressure is the force created by the meshing of the pump gears, and is expressed in pounds per square inch (PSI). Pressure moves the oil away from the pump. Vacuum is expressed in inches of mercury, and is abbreviated as in. Hg. Normally we simply show the numerical value of the Figure 4-3: Strainer screen and gasket. Figure 4-4: Suntec Industries; Cutaway example single stage fuel unit Diaphragm Valve Optional Return To Seal Chamber From Seal Chamber Easy Flow Bleed Valve Return Port Return To Inlet Inlet Port Cone Valve Chapter 4 Fuel Units and Oil Valves Caution: This valve must be set at the factory or authorized service station. Do not tamper with this in the field. Note: Do not try to adjust nozzle pressure with gauge in this port.
NORA Oilheat Technicians Manual
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