Chapter 4 Fuel Units and Oil Valves 4-12 Fuel Units and Oil Valves Figure 4-17: Pressure test Figure 4-16: Pressure tester If a fuel unit operating pressure of at least 100 PSI cannot be obtained, the problem may be, in addition to the above items, one of the following: 1. Worn pump gears. 2. Nozzle capacity beyond pump capacity. 3. Motor not up to speed. 4. Loose shaft coupling. 5. Defective pressure regulating valve. Pressure check at cutoff Once you are finished with the operating pressure check, shut off the burner. Insert a pressure gauge directly into the pump pressure port, Figure 4-17, and run the burner until the pump reaches its pressure setting and then shut the burner off. (Note that cutoff pressure cannot be measured at the bleeder port as the pressure regulating valve has an internal bypass system which does not hold pressure at the bleeder port on shutdown.) As soon as the burner shuts off, the pressure should drop very quickly about 10 to 25%, and then hold that pressure. The pressure cutoff reading should hold for at least five minutes without change. check. These checks can be made on some pumps by inserting a pressure gauge into a nozzle port, with others a tester may have to be used, Figure 4-16. You will need a pressure gauge capable of reading at least 300 PSI. First operate the burner to determine fuel unit pressure, which should normally be adjusted to 100 PSI or more depending on the burner manufacturer’s recommendations. Turn the pressure regulator adjusting screw (normally clockwise) until the pressure increases 40 to 50 pounds (but not above 200). If the pump cannot achieve at least 150 pounds, the pump gears or regulating valve are worn out and you should replace the pump. Then back off the pressure adjusting screw (counterclockwise) to the desired operating pressure. Uneven or fluctuating pressure can cause severe flame pulsation. A pulsating pressure reading (gauge needle jumps about from high to low) may indicate: 1. A partially clogged filter or pump strainer. 2. Air may be present in the pump caused by: a. Loose strainer chamber cover or defective strainer chamber gasket. b. Air leak in the suction line. c. Excessive intake vacuum. 3. Slipping pump coupling. Note: Slight regular vibrations of the needle are considered normal as the resonance frequency of gauges is very close to gearset frequency. Liquid filled gauges can help dampen or eliminate frequency vibrations and are preferred.
NORA Oilheat Technicians Manual
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