Page 62 of BGT (Difficult)

Question 1

Describe the dual manifold duplex fuel nozzle? (3)

Answer 1

• Pressuring valve may be employed to distribute the fuel to the manifolds.
• As fuel flow and pressure increases, the pressurising valve moves to gradually admit fuel to the main manifold and orifices.
• This gives a combined flow down both manifolds.

Question 2

What are the advantages of a duplex fuel nozzle compared to a simplex fuel nozzle?

Answer 2

• Are able to give effective atomisation over a wider flow range than the Simplex type for the same maximum fuel pressure.
• Efficient atomisation is obtained at the low flows that may be required at high altitude and startup.

Question 3

What is the valve in the duplex nozzle known as? Why?

Answer 3

• Fuel pressurising and Dump Valve.
• Dump is used at engine shut down, when all residual fuel in the manifold is dumped from the system to prevent vaporising within the system, leading to blockages.
• Also ensures a definite cutting off at shut down.