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  #1  
Old 07-18-2022, 04:18 PM
RV10Farmer RV10Farmer is offline
 
Join Date: Feb 2022
Location: Livermore, CA
Posts: 10
Default SDS EFI with dual fuel pumps

The folowing is a photo taken from http://www.sdsefi.com/lycoming6.htm, that shows two fuel pumps connected in parallel.



When one of the pumps fails, does it close off the fuel path, or does it leave it open so fuel can still flow in both directions? If a failed pump still allows fuel to flow, would that allow the output fuel from the other good pump to flow back toward the fuel tank, essentially not able to feed the full fuel flow to the engine ?

The SDS website's "Engine component deletion when ordering new engine" section says the fuel pump and pushrod are not needed anymore. I assume it meant only the engine driven fuel pump. The booster pump (not part of the engine order ?) is still needed ?

It is not clear if one still wants a booster pump, and if the booster pump can push fuel through the failed Walbro pumps. This is assuming the extremely unlucky case when both SDS EFI pumps failed.

RV10Farmer

RV10 builder number 42822

Last edited by RV10Farmer : 07-18-2022 at 04:21 PM. Reason: Typo and add signature
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  #2  
Old 07-18-2022, 04:59 PM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
 
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Location: Mojave
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These are two identical high pressure fuel pumps. Only one is needed to run to serve all the fuel needs of the engine. The other one is a backup. There is no mechanical pump in this scheme, and there is no "boost pump".

Each pump has a built in check valve at the outlet so if one is not producing pressure, the valve closes and the other pump continues to push fuel into the outlet manifold, against the closed check valve, and ultimately to the engine.

Fuel does not "flow in both directions" with this module. There is an inlet side and an outlet side. It just so happens that each (or both) pumps can move fuel from the inlet manifold to the outlet manifold.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI
1940 Taylorcraft BL-65
1984 L39C - SOLD
RV-8 - SDS CPI - SOLD

Last edited by Toobuilder : 07-18-2022 at 05:02 PM.
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  #3  
Old 07-18-2022, 05:10 PM
Ralph Inkster Ralph Inkster is offline
 
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Location: Calgary, Alberta
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If you are installing the SDS EFI/EI systems in your project, you would delete the mechanical fuel pump (& push rod) from your engine order. You would also have no need for a 'boost' pump.

I use both pumps in the SDS fuel pump module only during take off & landing so I would have continuous pressure if there were a failure in either during those critical stages of flight.
During normal cruise I normally have only one pump running & keep the second one as redundancy.
The electric fuel pumps have internal check valves to stop the fuel back flowing if one pump is turned off.
Some SDS builders setup their systems with low pressure or low power sensing switching that automatically turn on the redundant pump if it senses a problem in the primary pump. Personally, I just use a separate switch for each pump, I get an alarm of low pressure & manually switch to the redundant pump.
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Last edited by Ralph Inkster : 07-18-2022 at 05:12 PM.
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  #4  
Old 07-18-2022, 05:17 PM
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Toobuilder Toobuilder is offline
 
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Indeed. I have my second pump wired to a separate switch that is used as a "boost pump" just so I dont have to unlearn all that training. Takeoff and landing or "oh $hit" has me going for the "boost" switch, just like a Cherokee.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI
1940 Taylorcraft BL-65
1984 L39C - SOLD
RV-8 - SDS CPI - SOLD
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  #5  
Old 07-18-2022, 10:05 PM
RV10Farmer RV10Farmer is offline
 
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Location: Livermore, CA
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Default Clued in

Makes sense. I may go with the "boost" switch option too, because I don't want to introduce a pressure sensor, another potential point of failure.

Hope the SDS folks can see this and update the description for other builders.

RV10Farmer

Builder number 42822
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  #6  
Old 07-19-2022, 06:57 AM
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rv6ejguy rv6ejguy is offline
 
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The fuel system schematic on Page 2 of the main installation manual gives a good view of the pump connections. We'll add further descriptions on the check valves and operation on the next manual revision.
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 457.6 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ


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  #7  
Old 07-19-2022, 10:24 AM
agent4573 agent4573 is offline
 
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Quote:
Originally Posted by RV10Farmer View Post
Makes sense. I may go with the "boost" switch option too, because I don't want to introduce a pressure sensor, another potential point of failure.
No one can force you to do anything, but I would rethink not having a fuel pressure sensor. I don't think I've flown a low wing that didn't have fuel pressure feedback, and it seems even more important in a fully electric system. If you're not installing an O2 sensor, fuel pressure will directly affect your mixture ratio. If you're not monitoring that, a clogged filter or a partially failed pump can put you in a severe lean condition and you won't know about it until you blow the engine up.
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  #8  
Old 07-19-2022, 10:56 AM
Ralph Inkster Ralph Inkster is offline
 
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Quote:
Originally Posted by agent4573 View Post
No one can force you to do anything, but I would rethink not having a fuel pressure sensor. I don't think I've flown a low wing that didn't have fuel pressure feedback, and it seems even more important in a fully electric system. If you're not installing an O2 sensor, fuel pressure will directly affect your mixture ratio. If you're not monitoring that, a clogged filter or a partially failed pump can put you in a severe lean condition and you won't know about it until you blow the engine up.
In my post I was more referring to a power switching system that would activate the redundant fuel pump automatically if there was a pressure loss on the delivery system (as mentioned, I don't have this type setup - I use a separate switch to control each pump)
It would be a no brainer to have fuel pressure monitoring as normal instrumentation either to a gauge or engine monitor (with some sort of alarm).
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  #9  
Old 07-19-2022, 12:03 PM
RV10Farmer RV10Farmer is offline
 
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Location: Livermore, CA
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I was also referring to the sensor needed to automatically activate the "backup" pump. I can imagine a mal-functioning sensor causing thrashing among the two pumps. I do recognize the importance of having a fuel pressure sensor for the engine.

I'm clueless on O2 sensor still. Where is it installed ? Does it simply test the inflow air pressure ? Any pointers/links that I can follow to learn a bit more, if it can't be explained in less than a few sentences ?

RV10Farmer

Builder #42822

Last edited by RV10Farmer : 07-19-2022 at 12:17 PM.
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  #10  
Old 07-19-2022, 12:56 PM
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Mike S Mike S is offline
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Quote:
Originally Posted by RV10Farmer View Post

I'm clueless on O2 sensor still. Where is it installed ? Does it simply test the inflow air pressure ? Any pointers/links that I can follow to learn a bit more, if it can't be explained in less than a few sentences ?

RV10Farmer

Builder #42822
O2 sensor goes in the exhaust. It reads residual O2 and presents the reading as air/fuel ratio.

My SDS system has this option and it did require a stand alone box that actually reads the O2 sensor info and sends it out as a digitized signal to the SDS brain box. The actual readout of the AFR is shown on the SDS panel mounted controller for the hidden brain.

Until there is a wide spread availability of unleaded fuel for aircraft, the O2 sensor does not control the actual feedback to automatically lean the engine, but I believe the SDS brain is capable of doing in the future. Option that is not yet activated.

Ross needs to jump in here and give you the straight scoop in case I got some of this wrong........working off old memories from 3 or 4 years back.
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Flying as of 12/4/2010

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