OFTEC Oil Burner Types and Operation 3 — Questions and Answers
Question 1: What is the role of the pre-heater in an oil burner using gas oil (Class D fuel)?
- To warm the oil to reduce its viscosity for proper atomisation (Correct answer)
- To heat the combustion air
- To warm the boiler water before ignition
- To prevent the flue from cooling down
Correct answer: To warm the oil to reduce its viscosity for proper atomisation
Gas oil (35-second) is more viscous than kerosene. A pre-heater warms the oil before it reaches the nozzle, reducing viscosity so it can be properly atomised for clean combustion.
Question 2: What is the standard nozzle flow rate unit used for oil burner nozzles in the UK?
- US gallons per hour (USgph) (Correct answer)
- Litres per minute
- Cubic metres per hour
- Kilograms per second
Correct answer: US gallons per hour (USgph)
Oil burner nozzles are rated in US gallons per hour (USgph), even in the UK. Common domestic sizes range from 0.50 to 1.50 USgph. This rating is measured at a standard test pressure of 7 bar.
Question 3: What safety device prevents the oil pump from building excessive pressure?
- A pressure relief valve that returns excess oil to the suction side (Correct answer)
- The photocell
- The lockout switch
- The thermostat
Correct answer: A pressure relief valve that returns excess oil to the suction side
The pressure relief valve in the fuel pump prevents dangerous over-pressurisation by diverting excess oil back to the suction (return) side of the pump. This maintains safe, consistent operating pressure.
Question 4: In a two-pipe oil supply system, what is the purpose of the return pipe?
- To carry unused oil back to the tank, aiding in de-aeration (Correct answer)
- To supply a second burner
- To act as an overflow from the filter
- To provide ventilation to the oil tank
Correct answer: To carry unused oil back to the tank, aiding in de-aeration
In a two-pipe system, excess oil and any trapped air are returned to the tank via the return pipe. This helps remove air from the fuel line and ensures reliable priming, especially on longer pipe runs or where the tank is below the burner.
Question 5: What is the maximum recommended length for a single-pipe oil supply to a burner?
- 5 metres with a maximum lift of 3 metres (Correct answer)
- 20 metres with a maximum lift of 10 metres
- 50 metres with no lift restriction
- No limit as long as the pipe is copper
Correct answer: 5 metres with a maximum lift of 3 metres
Single-pipe systems are limited to approximately 5 metres total length with a maximum suction lift of about 3 metres. Beyond these limits, a two-pipe system should be installed to ensure reliable fuel delivery.
Question 6: What material is the oil supply line between the tank and burner typically made from?
- 10mm copper or steel (Correct answer)
- Plastic (PVC) pipe
- Rubber hose
- Cast iron
Correct answer: 10mm copper or steel
Oil supply lines are typically 10mm outside diameter copper tube or steel pipe. Copper is most common in domestic installations. Plastic pipe is not suitable for above-ground oil supply lines due to fire risk.
OFTEC Oil Burner Types and Operation 3
What is the role of the pre-heater in an oil burner using gas oil (Class D fuel)?