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Businessjet93
12-30-2018, 06:37 AM
What is the Difference between Fuel Primer pump and Fuel boost pump?

I saw the Cherokee 180 has Fuel Primer pump and Fuel boost pump either. If they do same thing, why there are two switch?

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PerfInit
12-30-2018, 01:45 PM
The Primer is used during cold engine starts only. The primer manually Injects a small amount of fuel directly into the cylinder head of a carburated engine. Think of the primer as a small “syringe” with a tube that goes directly to one cylinder. The electric fuel pump is for when the engine is running. It is a backup to the mechanical fuel pump and also provides more positive fuel flow during takeoff, landing and switching fuel tanks.

Businessjet93
12-31-2018, 08:50 PM
The Primer is used during cold engine starts only. The primer manually Injects a small amount of fuel directly into the cylinder head of a carburated engine. Think of the primer as a small “syringe” with a tube that goes directly to one cylinder. The electric fuel pump is for when the engine is running. It is a backup to the mechanical fuel pump and also provides more positive fuel flow during takeoff, landing and switching fuel tanks.

There is mechanical fuel pump but also electronic fuel pump? Why? I searched Jeppesen PPL but it doesn't have enough information about it.


Twin Wasp
01-01-2019, 12:53 AM
There is mechanical fuel pump but also electronic fuel pump? Why?


PerfInit said why - "It is a backup to the mechanical fuel pump and also provides more positive fuel flow during takeoff, landing and switching fuel tanks." I would add for starting too.

Fuel in low wing airplanes isn't going to move to the engine on its own. An electric pump provides redundancy and fuel under pressure when the mechanical pump isn't working. High wing airplanes use gravity to move fuel to the engine. The odds of gravity failing on any given flight is low enough there is no need for backup.

Businessjet93
01-01-2019, 02:42 AM
PerfInit said why - "It is a backup to the mechanical fuel pump and also provides more positive fuel flow during takeoff, landing and switching fuel tanks." I would add for starting too.

Fuel in low wing airplanes isn't going to move to the engine on its own. An electric pump provides redundancy and fuel under pressure when the mechanical pump isn't working. High wing airplanes use gravity to move fuel to the engine. The odds of gravity failing on any given flight is low enough there is no need for backup.


thanks for the answer.

But I mean, most of modern automobile have only Electronic fuel pump, not the mechanical fuel pump. I heard that mechanical fuel pump is used for only classic models.

So I wonder why there are mechanical fuel pump even there is electronic fuel pump?

PT6 Flyer
01-01-2019, 05:28 AM
why there are mechanical fuel pump even there is electronic fuel pump?

The mechanical fuel pump is the main pump. The electrical fuel pump is only a backup, in case the mechanical fuel pump fails. Many airplanes require the electrical fuel pump to be turned on for takeoff and landing, because these phases of flight are very critical. For this reason, both the main and backup fuel pumps are used during these phases of flight.

Be aware that "electronic" does not equal "electrical". There are no transistors in an electrical fuel pump.

Twin Wasp
01-01-2019, 06:48 AM
But I mean, most of modern automobile have only Electronic fuel pump, not the mechanical fuel pump. I heard that mechanical fuel pump is used for only classic models.

So I wonder why there are mechanical fuel pump even there is electronic fuel pump?

If the electric pump fails in your car (and if it is the only pump) you're stuck on the side of the road. If all you had in an airplane was an electric pump and it failed, where would you be?

rickair7777
01-01-2019, 06:56 AM
If the electric pump fails in your car (and if it is the only pump) you're stuck on the side of the road. If all you had in an airplane was an electric pump and it failed, where would you be?

Yes, this. Need a primary and a backup for safety-critical systems in aviation. Except for a few very reliable things like wing spars and engine blocks.

High wing: Primary = gravity, backup typically electric (just like two ignition systems).

Low wing: Primary typically mechanical, backup typically electric.

Jets: Lots of fuel pumps.

Same reason some gyro instruments are vacuum, others electric in older planes.

PerfInit
01-01-2019, 06:56 AM
^^^ Glider practice! Happy New Year to all. Great discussion! Auto motive design standards significantly differ from aviation.



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