Chapter 4—Fuel Units and Oil Valves 4-21 siphoning as well protect the pump from excess head pressure. When the burner comes on the pump creates a vacuum that pulls the valve stem down and opens the valve. When the burner shuts off, if there are no leaks the valve stem will stay down and remain in this position. If there is a leak between the PRV and the burner, the siphon created by the leak will close the valve, shutting off the oil supply to the line. If the red stem sticks out of the top of the valve, you know a loss of vacuum (siphon) has occurred. If the top of the oil supply source is more than 8 feet above the fuel unit you need to install a PRV. The NFPA rating for the head pressure on a fuel unit is only 3 PSI, about 8 feet. If the tank head (height of oil supply above the unit) is greater than 8 feet, the supply oil pressure may exceed 3 PSI and thereby shorten shaft seal life. If it is necessary to locate the tank at a greater height, a pressure reducing valve or an oil safety valve should be used in the oil supply line. Thermal safety valve A thermal safety shut off (Firomatic) valve should be installed in the suction line at the tank. The shut off valve should be UL listed and should be equipped with a fusible type handle that melts at 165°F. Also install a shut off valve before the filter and at the fuel pump for ease of service. If the tank is outside of the building, there should be a shutoff valve at the wall where the suction line enters the building. Foot valves Foot valves are check valves installed on the end of the suction line in underground tanks. They are no longer needed and not recommended; however, they were common on older installations and some are still in the field. It is not unusual for them to get stuck closed and not allow oil to flow. There are two options in this case: 1. Run new oil lines from the tank to the burner. 2. If the return line extends to the bottom of the oil tank, you can convert the system to a one-pipe system by capping the suction line and using the original return line as the new suction line. (Remember to remove the bypass plug in the fuel pump). Chapter 4 Fuel Units and Oil Valves Suntec has provided a very helpful Technical Bulletin and System Trouble Shooting Flow Chart which reviews the service procedures for both old and new style pumps, shown on pages 4-23 thru 4-25.
NORA Oilheat Technicians Manual
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