Question regarding Electric Fuel Pump

[Nirbm01]

Hello,

I am trying to find the reason why in the checklist when starting the engine the fuel pump needs to be on (after I am done with priming) - if the fuel pump is still on - don't I risk of flooding the engine?

What is the life span of the fuel pump? And how do I know that it needs to be replaced ?

Thanks.

[Chris]

I'm pretty sure I've never left the fuel pump on while starting the engine, but apparently it can be done without flooding it. I try to run it as little as possible since they have such a poor reputation.

What is the life span of the fuel pump? And how do I know that it needs to be replaced ?

You might want to check out this thread for more discussion on the lifespan of the aux fuel pump.

[smoss]

I've always questioned the order of the pump in the POH. My standard start is:
Throttle 1 inch
Mix full rich
Pump 3-5 sec on
Pump off
Mix off/cutoff
Throttle 1/2 inch
Start

This minimizes pump time but seems to accomplish the same thing, starts right up always. Made no sense to me why you should turn on the pump before opening the mixture, and leave it on while mix off. While this won't flood the engine (no fuel flow to engine with mix at cutoff, just flows in a circle) it seems like a waste of pump time.

[Nirbm01]

Thanks,

What about using it while change tanks? It seems that it is a hard to get part and it is failing after very little use.
Nir

[Chris]

What about using it while change tanks? It seems that it is a hard to get part and it is failing after very little use.

I don't use it for switching tanks. I only use it in three situations:

• priming before a cold start
• before landing
• if the fuel flow alarm sounds

[Rich]

What about using it while change tanks? It seems that it is a hard to get part and it is failing after very little use.

I don't use it for switching tanks. I only use it in three situations:

• priming before a cold start
• before landing
• if the fuel flow alarm sounds

I use it the same way but also use it during takeoff, for the same reason as on approach to landing.

[Chris]

I don't use it for switching tanks. I only use it in three situations:

• priming before a cold start
• before landing
• if the fuel flow alarm sounds

I use it the same way but also use it during takeoff, for the same reason as on approach to landing.

I stand corrected. I also use it during takeoff as well.

[David B]

Aside from how unreliable the Duke's pump has proven to be, I too only use my pump on cold starts, and take off. I have learned to monitor my fuel pressure constantly throughout a flight and unless I'm coming into a short runway, I don't even use it landing.

The interesting part about all of this is that we even need to use it for these phases of flight. I'd like to know why Diamond decided the mechanical pump was not reliable enough without the additional boost pump in critical stages of flight? I have yet to hear of a single DA40 that has had a mechanical pump failure and it makes me wonder why the POH requires so much use of the boost pump? Can anyone elighten me on this issue?

Thank you in advance...

[carym]

Aside from how unreliable the Duke's pump has proven to be, I too only use my pump on cold starts, and take off. I have learned to monitor my fuel pressure constantly throughout a flight and unless I'm coming into a short runway, I don't even use it landing.

The interesting part about all of this is that we even need to use it for these phases of flight. I'd like to know why Diamond decided the mechanical pump was not reliable enough without the additional boost pump in critical stages of flight? I have yet to hear of a single DA40 that has had a mechanical pump failure and it makes me wonder why the POH requires so much use of the boost pump? Can anyone elighten me on this issue?

Thank you in advance...

I know of one instance in a DA42 (which does NOT have boost pumps in the fuel tanks) where the pilot was slipping the plane on final. The slip caused some unporting of the fuel which led to a little engine missing. Luckily, there was no damage to the engine fuel pump (which I am told can be severely damaged if running without fuel going thru) although he did have ECUA&B failure appear that had to be repaired. The concept is that a fuel tank associated boost pump will keep fuel flow to the engine fuel pump if such a condition occurs and protect the engine and its fuel pump from having a problem.

[Rich]

Aside from how unreliable the Duke's pump has proven to be, I too only use my pump on cold starts, and take off. I have learned to monitor my fuel pressure constantly throughout a flight and unless I'm coming into a short runway, I don't even use it landing.

The interesting part about all of this is that we even need to use it for these phases of flight. I'd like to know why Diamond decided the mechanical pump was not reliable enough without the additional boost pump in critical stages of flight? I have yet to hear of a single DA40 that has had a mechanical pump failure and it makes me wonder why the POH requires so much use of the boost pump? Can anyone elighten me on this issue?

Thank you in advance...

There are various things that can theoretically occur at any time and cause an interruption in fuel flow. It might be momentary, but momentary at just the wrong time can have significant consequences. Failure of the mechanical pump is one, vapor lock in the low-pressure part of the system is another. The placement of the electric pump pressurizes the entire feed system and provides a backup for the mechanical pump. The DA40 is hardly unique in having the electric pump on for certain phases of flight.

I once had a Chevy S10 Blazer. I lived in Colorado at the time. It had an aftermarket electric fuel pump added, back near the fuel tank. Without it working, in summer, climbing up a grade (even the moderate Mt. Vernon I-70 grade), vapor lock would reduce the fuel flow where it would barely move.

The Cessna Cardinals, even though they had gravity-fed fuel from the wing tanks, also had a "fuel pump on" as normal takeoff procedure, as in climb mode the elevation difference between the fuel tanks and the engine could result in too low a fuel pressure at the fuel delivery point to the engine.