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  #1  
Old 04-14-2021, 02:00 PM
Av8torTom's Avatar
Av8torTom Av8torTom is offline
 
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Default Fuel Pumps

Question. Vans calls for the electric fuel pump and the engine driven fuel pump to be in series (carbureted engine). That is, fuel flows from the tanks, to the fuel selector to the electric fuel pump thru the gascolator to the engine driven pump to the carburetor.

Does anyone utilize parallel pump systems where both electric and engine driven pumps can deliver fuel to the carb independently of each other?

Is there ever a time when you have a engine driven pump failure that results in restricted fuel flow through the pump?

Thanks,

Tom
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  #2  
Old 04-14-2021, 02:50 PM
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Quote:
Originally Posted by Av8torTom View Post
Question. Vans calls for the electric fuel pump and the engine driven fuel pump to be in series (carbureted engine). That is, fuel flows from the tanks, to the fuel selector to the electric fuel pump thru the gascolator to the engine driven pump to the carburetor.

Does anyone utilize parallel pump systems where both electric and engine driven pumps can deliver fuel to the carb independently of each other?

Is there ever a time when you have a engine driven pump failure that results in restricted fuel flow through the pump?

Thanks,

Tom
They'd only be independent if you had a valve between them to select either one or the other (but not both).

Why? Are you considering doing this?
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  #3  
Old 04-14-2021, 02:55 PM
Avanza Avanza is offline
 
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Location: Vastervik Sweden
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Talking Fuel pumps

Most if not all low wing certified aircraft like the Piper PA28 have an electric and
a engine driven fuel pump in series.
The engine driven pump has membranes driven by a push rod from the camshaft. If this pump fails it will not block fuel flow.
The electric fuel pump can be a gear pump as well as a membrane pump.
I know of one company that sells electronic fuel injection that has two electric pumps with non return valves in parallel. But then there is no engine driven pump at all. They have separate power supply.
I would build according to the manual.
If you have two separate tanks, you could have one filter for each tank.
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  #4  
Old 04-14-2021, 02:56 PM
KayS KayS is online now
 
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Maybe no restriction, but if the second diaphragm fails the fuel should be transfered into the crankcase. Where fuel is not so helpful.
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  #5  
Old 04-14-2021, 03:21 PM
Avanza Avanza is offline
 
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Default pump failure

I think if the first membrane crack it will produce fuel in the over flow hose.
And yes if the second membrane fails this will transfer fuel to the crankcase.
The failure mode is usually a small crack in the membrane. It will leak but
in most cases the electric pump will provide required pressure to run the engine. A small amount of fuel in the crankcase will evaporate quickly.
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  #6  
Old 04-14-2021, 03:40 PM
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Quote:
Originally Posted by KayS View Post
Maybe no restriction, but if the second diaphragm fails the fuel should be transfered into the crankcase. Where fuel is not so helpful.
So are you suggesting a parallel arrangement?
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  #7  
Old 04-14-2021, 03:42 PM
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Quote:
Originally Posted by RV7A Flyer View Post
They'd only be independent if you had a valve between them to select either one or the other (but not both).

Why? Are you considering doing this?
I just want to be sure that if the mechanical pump fails, that the Facet electric pump will keep the fan spinning.
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  #8  
Old 04-14-2021, 03:48 PM
Freemasm Freemasm is online now
 
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Quote:
Originally Posted by RV7A Flyer View Post
They'd only be independent if you had a valve between them to select either one or the other (but not both).

Why? Are you considering doing this?
They are positive displacement devices with their own independent bypass regs/internal valving. No other valving would be reasonably needed.

The original system designs truly were/are examples of simple design elegance. Without the push for more efficiency and more horsepower from the existing power plants (slightly better hydro carbon missions is a side effect), the need/desire to replace these legacy systems with more complex EFI and related system changes would be very doubtful. My opinion of course but would love to hear any contrary thoughts. Back-up power sources and related gets very complex, very quickly. All that said, I'm planning both EFI and EI in my build.

Last edited by Freemasm : 04-14-2021 at 04:34 PM.
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  #9  
Old 04-14-2021, 05:01 PM
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There is nothing wrong with thinking through what you are installing in the airplane as you build, but as has been mentioned many times previously, fuel system design (or should we say “incorrect fuel system design”) is a leading cause of accidents in amateur built aircraft.

Add to that the fact that literally tens of thousands of low wing light aircraft (Certified and experimental) have been flying for decades With a fuel system that has an electric pump in series to an engine driven diaphragm pump. If there was a safer / better design it would have been incorporated long ago.
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  #10  
Old 04-14-2021, 06:47 PM
David Z David Z is online now
 
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Add to Scott's post, fuel injected high wing aircraft as well. I have never heard of parallel mechanical/electric fuel pumps used in aircraft. This is a case of "if it ain't broke, don't fix it" or "trying to invent a better wheel".

I have heard of parallel electric fuel pumps and no engine driven pump. The EFI system from SDS does this and there are the odd copies of that. But again, that's parallel electric pumps, and no mechanical pump.
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