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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.

rv10pump1.jpg


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
 
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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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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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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.
 
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
 
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.
 
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.
 
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).
 
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
 
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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.
 
O2 sensor system (AFR air fuel ratio monitor systems) are a highly recommended accessory for tuning your EFI system.
In the automotive world, they are the prime tool that regulates your car engines fuel metering.
They would be more popular on GA engines if it weren't for our leaded gas clogging them up prematurely compared to automotive usage (maybe someday when unleaded fuel rules, this will change), some sensors last as few as 50hrs, some last much longer into the hundreds of hours.
The O2 sensor mounts in one of your exhaust tail pipes, it registers the engine AFR and displays it on the SDS controller, or you could optionally have a separate gauge to show it's output. This would assist you in setting you fuel map in the SDS controller so you can program the appropriate AFR for every phase of engine operation - be it cold start - idle - taxi - run up - climb - cruise - decent - etc. You can also use it to set LOP.

Someday, when we have easy access to unleaded fuels, we could actually turn on the CLOSED LOOP function in our SDS modules and rely on the O2 sensor to properly regulate AFR parameters and not have to worry about it again - but for now we are stuck running OPEN LOOP and rely on our individually programmed fuel mapping (greatly assisted in programming using our fragile AFR monitors output values) to run our engines on... till that someday comes...
 
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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).

There is a way to tie the backup pump power to the programmable "low fuel pressure" warning in your EFIS. That way you only need the single fuel pressure sender and it comes on automatically when you lose pressure on the first pump. But I agree with you, I just use 2 switches and turn the 2nd one on during critical phases of flight.
 
The most common power switching system for fuel pumps is much more simple, but relies on a "meat servo" to activate the switch. You have two of them coming out each shoulder :D.

An automatic pump switching system gets pretty complex when you want to turn off the engine. Engine problems in flight. Basically any time you would WANT no fuel pressure has to have the logic engineered into the system. Much easier to do what we have all been doing for years and turn it on yourself.
 
Use both pumps during critical phases of flight then alternate between pumps depending on the day, even or odd days. That way pumps get more equal time in service.
 
A previous post got me to thinking... I'm used to a manual mixture knob, that when you're ready to shut down you pull it to full lean, and let the engine die that way.

With this system, with no mixture knob, do you kill your engine by just turning off both pumps, and letting the pressure drop to a point of no longer providing sufficient fuel for shut down?

Thanks,
Lance
 
A previous post got me to thinking... I'm used to a manual mixture knob, that when you're ready to shut down you pull it to full lean, and let the engine die that way.

With this system, with no mixture knob, do you kill your engine by just turning off both pumps, and letting the pressure drop to a point of no longer providing sufficient fuel for shut down?

Thanks,
Lance

There is a mixture knob in this system so you can kill it that way if you wish. Most are just turning off the pumps but you can kill with ECU, or coil power too.
 
A previous post got me to thinking... I'm used to a manual mixture knob, that when you're ready to shut down you pull it to full lean, and let the engine die that way.

With this system, with no mixture knob, do you kill your engine by just turning off both pumps, and letting the pressure drop to a point of no longer providing sufficient fuel for shut down?

Thanks,
Lance

I kill the engine by shutting down the fuel pumps.

I arranged the ECU, coils, and fuel pump switches in line, starting is turn on left to right, shutting down is turning off right to left. Easy to remember and simple to do.
 
I did exactly what Mike did on my switch setup and love it. I also use both for critical phases and alternate pumps on each flight to keep both working (somewhat) equal amounts. It's a great system and once we have unleaded fuel, I can't wait to start using the O2 sensor even more!
 
Lots of complication in switches here...

Is there any need to kill ignition in flight but leave the ECU and pump powered?

How about no pump but ECU and ignition?

How about no ECU, but pump and ignition.

Any of the above results in immediate shutdown.

Why be different than the billions of cars with trillions of hours in service?
 
Lots of complication in switches here...

Is there any need to kill ignition in flight but leave the ECU and pump powered?

How about no pump but ECU and ignition?

How about no ECU, but pump and ignition.

Any of the above results in immediate shutdown.

Why be different than the billions of cars with trillions of hours in service?

Simple answer is---run up check, I get to turn off each coil, and each fuel pump.
 
Why would you need to turn off a pump? If the engine is running, the pump is on. Turning on the second "boost pump" is obvious in a slight jump in fuel pressure and big jump in amperage. fuel pump ops check check complete.

In my airplane the coils are killed by the CBs.

CPU function is with the standard "pri/both/sec" switch.

But powering it all is a single "Engine On/Off" switch that controls the engine buss.
 
Why would you need to turn off a pump? If the engine is running, the pump is on. Turning on the second "boost pump" is obvious in a slight jump in fuel pressure and big jump in amperage. fuel pump ops check check complete.

In my airplane the coils are killed by the CBs.

CPU function is with the standard "pri/both/sec" switch.

But powering it all is a single "Engine On/Off" switch that controls the engine buss.

Yes, there is merit in operating the pumps as you describe, but one advantage in having both pumps on separate switches is you could rotate the 'primary' function between the two pumps, potentially extending the life of them. This is what I do.

As I check the coils before each flight, I'd rather do it with a switch rather than a CB heeding the (probably arguable) old advise stating that breakers should not be used for switching functions. I marked my coil switches with 'IGN' so other pilots might better relate to the mag check mindset.

The pri/both/sec switch (6 cyl) & pri/sec (4 banger) selects which module FI mapping program the engine is running on at the moment. As the primary has the full sensor inputs & most reactive fuel mapping functions, I leave the 'sec' FI module for redundant purposes only. I check it once on run up.

I treat the main power input to the engine buss same as you, but put it on a OFF/ON/(Start) key switch. I have only ever turned the SDS off in flight to test & that was right over an airport (actually not advisable you do this).

I believe it's best to separate & guard critical switches.
 

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Fuel pump life is certainly a concern, but I address that issue by simply switching the power leads at the pumps every CI. Kind of like rotating spark plugs.

And yes, after 35 years in military aviation where CB's are used as switches all the time, I am making the informed choice to ignore the "old advice".
 
Lots of complication in switches here...

Is there any need to kill ignition in flight but leave the ECU and pump powered?

How about no pump but ECU and ignition?

How about no ECU, but pump and ignition.

Any of the above results in immediate shutdown.



One more thing, in the installation instructions Ross says to have two ign, and two fuel pump switches, and an optional ECU switch.

Why be different than the billions of cars with trillions of hours in service?

Cars dont fall out of the sky?
 
First off - to each their own.

I run the dual pump module from SDS, with two switches. Every time I switch tanks, I also switch pumps. Left for left, right for right. It makes zero difference in how the fuel flows, but it keeps both pumps in service without long periods of downtime, and if one of them is dying I'll know it very quickly. The switches are also closer in my field of view than the tank selector for knowing which tank you are burning from. I've had a fuel pump failure (AFP, not SDS) so my personal viewpoint is that I want to exercise them both looking for weakness.

Yeah, I know - I'm wearing out my switches. I'm also wearing out my fuel pumps. And my engine. And my prop. And everything else along with it. One day I'm gonna die, and all my babies are probably gonna be born naked. I'll get over it.
 
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