TM 5-3895-374-24-2Figure 24Typical Oil Burner with Low-High-Off or Low-High-Low Fuel/Air Control Mode Using a Two-Step Oil Pump. (Model C-0)MECHANICAL OPERATION: This Low-High-Off system uses aTwo-Step Oil Pump with a simplex Oil Nozzle (14) in conjunctionwith movable Air Dampers (4) to provide a low fire start and a highfire run sequence. A direct spark oil ignition system will normallybe supplied, but certain insurance company codes could require aspark ignited gas pilot to provide ignition for the main oil flame.Nozzle flow rate pressure is taken at the 118” Plugged PumpPressure Gauge Port (6). The low fire oil rate is set by adjustingthe Oil Pump Low Pressure Regulator (8). The high fire oil flowrate is set by adjusting the Oil Pump High Pressure Regulator (3).For both high and low fires turn the adjustment screws clockwiseto increase the pressure and counterclockwise to decrease thepressure to the Nozzle. Approximate low fire oil pressures are 100to 125 psig and high fire, 200 to 300 psig. Both settings will varydepending upon the specific nozzle size selected and jobconditions. See pages 30-31, Tables 8 & 9 for specific nozzlepressures and flow rates. At light off the Main Oil Solenoid Valve(1) is energized, allowing fuel to the Nozzle. A normally openpump mounted Oil Solenoid Valve (7) allows a controlled flow of oilto the Nozzle in accordance with the pressure setting of the pumplow fire adjustment. When the low fire flame is proven by theflame detector*, the pump mounted, normally open Solenoid Valveis energized (closes), putting full high fire pump pressure on thenozzle. Simultaneously, the Three-WaySolenoid Valve (10) is energized, allowing oil into the Hydraulic OilCylinder (9) which mechanically drives the Air Damper Arm (13) tothe high fire open position. The burner operates at full high fireuntil the system demand is satisfied. This depiction shows the AirDampers and the Hydraulic Cylinder at the low fire light offposition.The Low-High-Low systems are identical to the Low-High-Offsystem, except that an additional temperature or pressurecontroller is added to the system. At a selected preset point, it willelectrically switch the Oil Valves and Air Damper components toplace the firing rate either in the low or the high fire run position.When the burner is running at high fire and the controller calls forlow fire, the normally open pump mounted Solenoid Valve (7)(which is closed at high fire) is de-energized (opens), reducingnozzle pressure to the low fire rate. Simultaneously, the Three-Way Solenoid Valve (10) is de-energized, allowing oil to flow out ofthe Hydraulic Cylinder back to the Pump (2) and driving the AirDampers (4) to the low fire position. Depending on loadconditions, the burner can alternate indefinitely between the lowand the high fire positions, without shutting down. When systemdemand is satisfied all fuel valves are de-energized and the AirDampers are placed in the light off position for the next start up.The Air Damper position for low fire run and light off position areone and the same in this system. The opening distance of(page 3-970)
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