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Purpose of a turbine fuel pressurizing valve

Aviation Mechanic Powerplant (AMP) practice question 19 of 20 on Engine Fuel and Fuel Metering Systems. ACS element AM.III.I.K14 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONOn a turbine engine that uses duplex fuel nozzles, what is the purpose of the fuel pressurizing valve?

  1. ATo bypass fuel back to the pump inlet
  2. BTo divide flow into primary and secondary
  3. CTo hold fuel temperature above freezing point
Show the answer and explanation

Correct answer: B. To divide flow into primary and secondary

  • A — incorrect Bypassing excess fuel back to the inlet is the job of the pump pressure relief valve, which handles the excess capacity of the gear-type main stage.
  • B — correct A pressurizing valve is usually required on engines with duplex nozzles to divide the flow into the primary and secondary manifolds as fuel demand increases.
  • C — incorrect Keeping fuel above freezing to prevent filter icing is the function of the fuel heater, not of a valve in the nozzle manifold circuit.

BACKGROUND

A fuel pressurizing valve is usually required on engines incorporating duplex fuel nozzles in order to divide the flow into primary and secondary manifolds. The fuel needed for starting and altitude idling passes through the primary line, and as fuel flow increases the valve begins to open the main line until at maximum flow the secondary line is passing approximately 90 percent of the fuel. Pressurizing valves usually trap fuel forward of the manifold, giving a positive cutoff. That cutoff prevents fuel from dribbling into the manifold and through the nozzles, which limits afterfires and carbonization of the nozzles. A flow divider performs essentially the same function; identical functions often carry different names between engine manufacturers.

STUDY TIP

Remember that the pressurizing valve does two jobs: it splits primary from secondary flow and it gives a positive cutoff that stops nozzle dribble. Treat flow divider and pressurizing valve as interchangeable names for the same function.

KEY POINTS

  • A pressurizing valve divides fuel between the primary and secondary manifolds of duplex nozzles.
  • At maximum flow the secondary line carries about 90 percent of the fuel.
  • Trapping fuel forward of the manifold gives a positive cutoff that limits afterfires and carbonization.

SOURCES

  • amp-powerplant/ch02.txt "Fuel Pressurizing & Dump Valves"
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MORE ON ENGINE FUEL AND FUEL METERING SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.