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NORA Oilheat Technicians Manual

Chapter 4 Fuel Units and Oil Valves Chapter 4—Fuel Units and Oil Valves 4-13 Any decrease from the cutoff pressure indicates a defective or dirty pressure regulating valve (piston or piston seat) that will result in oil dribbling from the nozzle and an after fire. The fuel pump should be replaced in this case. Field vacuum check While there are many reasons for the following problems, one of the leading possibilities is a leaking suction line, fittings or gaskets. If there is no other obvious cause for these problems, you should take an operating vacuum test to determine if you have a leak. 1. Pulsating pump pressure 2. Oil pump noise 3. Hard starting (ignition) 4. Poor flame retention 5. Noisy fire 6. Loss of flame during running cycle 7. Burner flame will not establish after long shutdown 8. After fire Checking system vacuum The first step is calculate what the vacuum should be, then test to see what it actually is and compare the two. To calculate the vacuum, figure about 1" of vacuum for each foot of oil lift, 1" of vacuum for each 10 feet of horizontal run, and ½" for a clean oil filter. If the actual operating vacuum is significantly less than the calculated vacuum, you probably have a leak either in the pump or somewhere in the line. To do this test, a vacuum gauge capable of reading 30" of vacuum should be screwed into the unused intake port. It is important that the vacuum gauge be securely tightened so that vacuum leaks will not develop around the threaded fittings. If the unit to be tested is set up for a one-pipe system, a return oil line from the unit nozzle port should be provided to catch the oil removed from the strainer chamber during the vacuum check. Then run the burner, bleed the pump, and read the vacuum. The vacuum reading should approximate the calculated vacuum. If the gauge reading is substantially above the calculated vacuum, there is a restriction in the oil supply that may be caused by of one of the following: 1. Plugged fuel filter 2. Kinked oil supply line 3. Partially closed oil supply valve 4. Check or foot valve inoperative or sticking Note: The excess vacuum caused by a partially clogged pump strainer cannot be read on the gauge. Be sure to look at the strainer through the inlet port before installing the gauge. If it appears dirty, remove the strainer and clean or replace it. If vacuum reading is below the calculated operating vacuum, the probable causes are: 1. Clogged pump strainer 2. Air leak in the suction line or suction line fittings 3. A suction leak around strainer chamber cover plate and gasket 4. Worn pump gears


NORA Oilheat Technicians Manual
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