Answers - Engine Fuel Systems


1. b
When an aircraft's boost pump pressure exceeds that of the primary fuel pressure pump, a bypass valve in the pressure pump opens and allows fuel to flow directly to the engine. This occurs during start, when the pressure pump is not operating, and any time the engine driven fuel pump becomes clogged or fails.

2. c
A positive displacement pump provides a fixed quantity of fuel per pump revolution. With a centrifugal-type fuel boost pump, once the pressure builds to a predetermined pressure, fuel bypasses the impeller and remains in the fuel tank. Therefore, the pump does not continually displace fuel and is not a positive displacement pump.

3. a
According to the 14 CFR 23.995, the engine fuel shutoff valve may not be located on the engine side of the firewall.

4. c
The primary purpose of a fuel boost pump is to provide a positive flow of fuel to the engine driven pump.

5. b
A fuel transfer ejector helps transfer fuel from the main tank to the boost pump sump by creating a low pressure area at the fuel pick-up point. By pumping fuel past the venturi in the injector, a low pressure area is created that drains fuel into the line that feeds the boost pump sump.

6. b
When an aircraft's boost pump pressure is greater than that of the main pressure pump, a bypass valve in the pressure pump opens and allows fuel to flow directly to the engine. This prevents a damaged or inoperative pump from blocking fuel flow to the engine.

7. a
The purpose of the engine-driven fuel pump is to deliver a continuous supply of fuel at the proper pressure at all times during engine operation. Therefore, a positive displacement pump must be used. One type of positive displacement pump that is widely used is the rotary-vane-type fuel pump.

8. c
One of the many purposes of a boost pump is to supply fuel under pressure for priming prior to starting an engine.

9. b
Engine-driven fuel pumps typically discharge more fuel than an engine requires. Therefore, fuel systems must incorporate a relief valve to prevent the build up of excessive fuel pressures at the carburetor. A typical fuel pump relief valve is spring-loaded and, when opened, allows excess fuel to flow back to the inlet side of the fuel pump.

10. c
The purpose of the engine-driven fuel pump is to deliver a continuous supply of fuel at the proper pressure at all times during engine operation. Therefore, a positive displacement pump must be used. One type of positive displacement pump that is widely used is the rotary-vane-type fuel.

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