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  #21  
Old 10-22-2014, 08:41 AM
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Snowflake Snowflake is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
With an EFI/ return type system, as soon as you turn the pump on without the engine running, 100% of the fuel is returned back to the tank at very high flow so fuel is immediately all mixed up with any water that might be in there.
If the gascolator is between the fuel tank and the point in your fuel system where the return line connects, then even if the fuel is running in bypass mode and looping back to the tank, it's getting circulated through the gascolator every time it goes through. Doesn't that remove water as it goes?

Bear with me, i'm just trying to understand...
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  #22  
Old 10-22-2014, 09:53 AM
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Quote:
Originally Posted by terrye View Post
For my system with Bendix fuel injection, I will have an Andair 70 micron gascolator in each wingroot to protect the pump, and a Falls Filtration 17 micron gascolator on the firewall to protect the injection servo.
Terry, might want to skip that 17 micron filter. A Bendix servo has a built-in 74 micron tubular screen accessible by removing the inlet fitting. That would suggest a 17 micron filter is unnecessarily restrictive, in particular if installed inline prior to the engine driven fuel pump.

Quote:
Originally Posted by rv6ejguy View Post
With an EFI/ return type system, as soon as you turn the pump on without the engine running, 100% of the fuel is returned back to the tank at very high flow
Quote:
Originally Posted by jrs14855 View Post
In even a minor fender bender these gascolators could be damaged and now you had fuel running all over.
Fuel release after damage is an additional risk factor for a system with a full-time electric pump (no engine driven pump). Fuel is pumped in high volume, and pumping does not cease when the prop stops. With a recirculating FI system, the high volume flow extends all the back through the return system plumbing, increasing the number of components exposed to damage. In cars, the problem of fuel flow after impact is sometimes addressed with a G-switch. In a forced landing, a good pilot will probably remember to kill the electrical supply prior to impact. I'm not sure how an auto-cutoff might be incorporated for an aircraft. People do forget things under pressure, and few accidents are planned.

Quote:
Originally Posted by Snowflake View Post
...even if the fuel is running in bypass mode and looping back to the tank, it's getting circulated through the gascolator every time it goes through. Doesn't that remove water as it goes?
The very high flow rate of a recirculating system would not allow water to settle in the cup.
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Last edited by DanH : 10-22-2014 at 09:57 AM.
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  #23  
Old 10-22-2014, 11:03 AM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by DanH View Post
Terry, might want to skip that 17 micron filter. A Bendix servo has a built-in 74 micron tubular screen accessible by removing the inlet fitting. That would suggest a 17 micron filter is unnecessarily restrictive, in particular if installed inline prior to the engine driven fuel pump.





Fuel release after damage is an additional risk factor for a system with a full-time electric pump (no engine driven pump). Fuel is pumped in high volume, and pumping does not cease when the prop stops. With a recirculating FI system, the high volume flow extends all the back through the return system plumbing, increasing the number of components exposed to damage. In cars, the problem of fuel flow after impact is sometimes addressed with a G-switch. In a forced landing, a good pilot will probably remember to kill the electrical supply prior to impact. I'm not sure how an auto-cutoff might be incorporated for an aircraft. People do forget things under pressure, and few accidents are planned.



The very high flow rate of a recirculating system would not allow water to settle in the cup.
I agree, 17 microns is smaller than you need here. We use a 35 micron sintered bronze filter on our dual pump module and these are well proven in tens of thousands of flight hours in aircraft.

For fuel pump cutoff in the event of a forced landing, our ECU will shut off the pump after 2.8 seconds of not detecting crank rotation.

Ditto the comment that on these systems, the high mixing and flow rates basically make collection of water in the gascolator cup improbable- therefore useless in that capacity.
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  #24  
Old 10-22-2014, 12:15 PM
Tom Martin Tom Martin is offline
 
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I have my sumpable filter (Andair gascolator) installed in the stick bay in the cabin. In this location it is just after the selector and before the boost pump. I have done this same mounting in numerous aircraft, including an RV10. It keeps this unit cool and isolated from vibration. It is easy to reach down under the cabin and get a sample before flight.
As I understand this thread, the only installation that perhaps should not use one of these units is a full automotive fuel type system. I will certainly take a look at the different options if I ever go that route, until then I will stay with what has safely worked for me.
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  #25  
Old 10-22-2014, 02:13 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
I agree, 17 microns is smaller than you need here. We use a 35 micron sintered bronze filter on our dual pump module....
I was suggesting the additional filter was unnecessary with an RSA-5.

Quote:
For fuel pump cutoff in the event of a forced landing, our ECU will shut off the pump after 2.8 seconds of not detecting crank rotation.
Yes, with the fuel pump relay control option installed in an SDS EM-5. Probably have that on your own RV-6.

However, the OP is thinking about installing a Protec EFii system. It drives the pump relay from the optional Bus Manager (not the ECU), in order to incorporate automatic pump switching. Pump #1 is always powered from the essential bus or emergency bus; the pump is wired to the NC relay terminal. And anyway, the Protek ECU harness doesn't seem to include a pump relay control wire. Have the systems been revised?

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  #26  
Old 10-22-2014, 02:42 PM
Bevan Bevan is offline
 
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[quote=DanH;927074]Terry, might want to skip that 17 micron filter. A Bendix servo has a built-in 74 micron tubular screen accessible by removing the inlet fitting. That would suggest a 17 micron filter is unnecessarily restrictive, in particular if installed inline prior to the engine driven fuel pump.QUOTE]

Agreed 17 micron may be overly restrictive. Not sure about the Bendix but my Precision FI system (which I understand is the experimental version of the Bendix) requires a filter (stated as 32 micron in the literature) either immediately before or after the mechanical fuel pump. This is to protect from larger volume of debris (conceivably fuel pump rubber diaphram debris) obstructing the smaller fine filter within the servo itself.

I was not able to find a 32 micron filter other than paper element type which I did not want. I was able to find a 40 micron cleanable mesh filter that fit inside the AP filter housing I had on hand now relocated downstream of the mechanical fuel pump. This was acceptable to the tech at Precision I was working with.

Bevan
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  #27  
Old 10-22-2014, 02:43 PM
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Mike S Mike S is offline
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Quote:
Originally Posted by DanH View Post
In cars, the problem of fuel flow after impact is sometimes addressed with a G-switch. In a forced landing, a good pilot will probably remember to kill the electrical supply prior to impact. I'm not sure how an auto-cutoff might be incorporated for an aircraft. People do forget things under pressure, and few accidents are planned.

This was a subject that got a lot of attention after Kyle Franklin's crash, that killed his wife------although it was smoke oil, not gasoline. But either one will fuel a fire.............

As I recall, Kahuna developed a G switch to cut off smoke oil-------perhaps it could be used in this situation also???
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  #28  
Old 10-22-2014, 03:57 PM
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rv6ejguy rv6ejguy is offline
 
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35 microns is about .0015 inches- much smaller than any orifice in an EFI injector. 17 micron is just overkill IMO with any FI system and unless it has a larger filtering area, perhaps restrictive in some cases.

Cars usually have both G switches, roll over switches and the ECU which can cut off the fuel pump in the event of an accident- food for thought in aircraft with electric pumps of any kind.

I couldn't comment on the recommended EFII fuel pump control layout. Robert will probably pipe up here.

I'd say about 1/3rd of our SDS aviation customers use the standard ECU controlled fuel pump relay, the rest, like me, use separate switches directly controlling the pumps. Preference really.
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  #29  
Old 10-22-2014, 07:37 PM
terrye terrye is offline
 
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Default Gascolator

My fuel filter selection was driven by the “Installation and Detail Specifications for the Silver Hawk EX-5VA1 Servo Kit” manufactured by Precision Airmotive.

Section 4.0 Fuel Filtration
The fuel supplied to the servo shall be filtered to 32 micron nominal. This filtration may occur prior to the engine driven pump, but all other pumps and valves shall be upstream of the filter.

I corresponded with Precision Airmotive when I was having trouble finding such a filter and was advised as follows:

We recommend a nominal 32 micron filter because the finger screen in the inlet of the servo is 70 micron and is not meant to be a primary filter. We agree that most certified aircraft should have a similar filter installed but we have no way of knowing what they use as they are separated from us by the engine manufacturer, which gives engine installation specs. Also, from our experience, many do not use a sufficiently fine filter.

I selected an Air Maze brand fuel filter from Falls Filtration with a filtration rating of 20 micron nominal (17 microns in my earlier post was in error) as this was as close to the 32 micron requirement that they could provide. Nominal describes the ability of the filter media to retain the majority of particulate (at 60%-98%) the rated pore size.
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  #30  
Old 10-22-2014, 07:48 PM
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rcpaisley rcpaisley is offline
 
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Default EFII pump control

EFII fuel pump management is handled automatically by the Bus Manager (if so equipped). Otherwise it is controlled by a builder supplied switch.
It is not part of the EFII wiring.

Robert
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