Unit 13 Oil-Burning Equipment

1. Unit 13 Oil-Burning Equipment

2. OBJECTIVES After studying this Unit, the reader should be able to • List and describe the products of combustion • List and describe the parts of a high pressure oil burner • Interpret oil burner wiring diagrams

3. PRIMARY CONTROL UNIT • Controls burner operation and safety functions • Utilizes a low-voltage control circuit • Can use a cad cell to detect flame in the chamber • Resistance of the cad cell decreases when flame is detected in the chamber • Cad cell controls the safety functions of the primary control

4. CAD CELL SAFETY CONTROL • The resistance of the device drops as it senses more light • The safety switch can shut down the burner • A cad cell that senses no light will have very high resistance • A cad cell that senses light should have a resistance of 600 - 1000 ohms

5. STACK SWITCH or STACK RELAY • Utilizes a bimetal actuated switch • Located in the stack and used as a safety switch • Will shut the burner down if heat is not sensed in the stack after a predetermined time period • Has hot contacts and cold contacts • Hot contacts are closed when the stack is hot • Cold contacts are closed when the stack is cold

6. OIL FURNACE WIRING DIAGRAMS • Includes wiring for the fan, the oil burner primary, and 24-volt control circuits • The limit switch is a safety that passes power to the primary control • On a call for heat, power is passed to the ignition transformer, burner motor, and fuel valve • The safety device will shut the burner down in case of a problem

7. STACK SWITCH SAFETY CONTROL • Positioned in the flue pipe • Bimetal gets heated by the combustion flue gases • Hot contacts allow the burner motor to continue to operate • Cold contacts allow current to flow through the safety switch heater

8. FUEL OIL SUPPLY SYSTEM • Fuel systems are either one-pipe or two-pipe systems • Fuel filter should be installed on oil supply line to burner pump • Viscosity is the thickness of the oil • Oil viscosity will change as the temperature changes • Viscosity affects the oil flow rate • Filter should be located between tank and the pump

9. COMBUSTION CHAMBER • Atomized oil is burned in suspension in the combustion chamber • Oil not ignited in suspension will hit the chamber walls and condense • Oil vapor hitting chamber walls and condensing will lower combustion efficiency • The burner must be matched to the chamber

10. HEAT EXCHANGER • Exchangers transfer the heat from combustion to the air that is circulated to heat the structure • Heat exchangers also separate flue gases from the air circulated to heat the structure • Heat exchangers should be inspected during normal service for cracks • Some states allow cracked heat exchangers to be welded, but most do not • Correct airflow is important across the heat exchanger

11. CONDENSING OIL FURNACES • More efficient than conventional furnaces • Combustion system includes: burner and related components, combustion chamber, as many as three heat exchangers, and vent fan and pipes • Heated air circulation system includes: blower fan, housing, motor, plenum and duct system • Third heat exchanger is a coil type where the temperatures are reduced below dew point • At the dew point temperature, a change of state occurs • Water vapor in flue gases condenses

12. Unit Summary • Ignition transformers and electronic igniters provide the high voltage needed for spark ignition • The primary control controls burner operation and safety functions of the system • Primary controls can use cad cells or stack relays • The resistance of a cad cell decreases as the amount of light sensed increases • The stack relay responds to the stack temperature