The CD position (if I recall correctly from my delivery visit to Duluth last September) is that this particular engine-driven fuel pump is extremely reliable. Apparently, complete failures are not known t have occurred. Therefore, the boost pump is supposed to be adequate for the likely failure modes.
My memory may be faulty, but I think this is what I was told when I asked the same question.
George
N747SJ
As I understand it, FAR Part 23 (under which Cirrus planes are certified) has the requirement that an auxiliary fuel pump cannot flood a running engine. Therefore, the pressure from the electric fuel pump is limited. This is also one reason why you have to prime so long for a cold start.
-Mike
I was under the assumption that a fuel pump could not flood an engine. WIth a carb, the pump fills the fuel bowl and when full, the float shuts off the fuel flow via a valve. The electric pump has a shut off to limit the pressure in the system.
I’m not sure about fuel injectors, but I assume that is the injectors that control the fuel metering in the cylinders and not the fuel pump.
I could be wrong and would appreciate any comments from an expert.
Walt N224AZ
I’m far from an expert, but I remember hearing of some airplanes that could be flooded in flight with the electric fuel pump. Can’t cite any examples, though.
If you switch the Cirrus fuel pump to “BOOST” in flight, you will notice two things: The fuel flow increases and, if you’re flying rich of peak, the EGT decreases. Based on this, it would seem that an auxiliary fuel pump can affect the mixture going to the cylinders
Are there any genuine experts out there who know the whole story?
-Mike.
FWIW…I checked my old Warrior POH. It states “An auxiliary electric fuel pump is provided in case of failure of the engine drive pump.”
Yep, need a genuine expert to sort this out.
Take care,
Walt N224AZ
I’m not an “expert” in fuel systems but I know of several aircraft in which the boost pump can flood the engine and cause a significant power loss. The Continental IO 470 and 520 engines that power Barons come with a three position boost pump - off, low and high. High is to be used only for start and if the engine driven pump fails. Low is used for ground operation in hot (vapor lock) conditions, takeoff and climb. If High boost is used while the engine driven pump is operational it is quite possible to flood the engine.
I just caught G. Savage’s post about the reliability of the engine-driven pump and will double check with Cirrus when I pick up my plane in TWO WEEKS.
I realize you can’t have two of every thing, but it would be good to understand the rational.
Walt N224AZ
See page 37 of the SR22 Training Manual for more specifics about the fuel pump. (That was the page in the Wings Aloft version. Might be different now.)