Unit 13 Oil-Burning Equipment

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

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

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

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

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

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

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

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

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

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

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