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01-17-2019, 04:23 PM
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Join Date: Aug 2017
Location: Sebastopol,CA
Posts: 358
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Quote:
Originally Posted by lr172
If concerned about running on battery power (no alternator), I would study that chart a bit more. At 12 volts (assume you are using standard FI) the flow falls off really fast at 25 PSI. Your pattery will be going down from 11.8 to 11 volts during the bulk of it's draw off and I assume the fall off is even worse as the voltage drops. If your pump is 10% off their test data, you may not be able to deliver 10 GPH at 25 PSI at 12 volts. Given that you can't control the relief valve, it will keep trying to make that pressure, even down to 0 flow.
The specs at 13.5 volts are still not pretty. You are only delivering 10 GPH at 25 PSI. That is not a larger margin of safety.
Larry
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Larry- Your concern is well taken, but my “backup” battery will be a fully charged EarthX EXT900VNT rated at 16AH., and these maintain pretty flat Voltage at 13.3 V or so right to the end. Its twin is also likely to have a substantial charge as well if I notice the flashing light and low-voltage indications from my G3X touch before it discharges too much. The engine will cruise fine at 7GPM delivered as low as 20PSI(Airflow Performance FI). The essential loads will be one fuel pump and one lightspeed.
When everything is working, I will have the option of running both fuel pumps with impunity, and one will be adequate for all cruise conditions with my 180 lyc. so it is advantagous to have the individual fuel pumps be as small as possible for the very reason that it permits sustained battery power operation for the longest duration. Any surplus capacity would simply result in more flow through the relief valve, reducing range. I will routinely take off and climb with both pumps operating. Admitedly, if the engine were even increased to 200HP, I’d have no choice but to go up one size on the pump.
ALL of this is made possible by the vented EarthX, and the pair of them together weigh 5lb less than the one PC680 I have removed, but pack more than twice the capacity and four times the CCA of the 680.. The two batteries are absolutely symmetrical, and either, but never both, can serve as primary or backup at any given moment. Note that each pump has its own external relief valve, and presumably I’ could switch to the other if a sticky valve indicated high pressure..- Otis
__________________
Otis Holt-
RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2019 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"
Last edited by Hartstoc : 01-17-2019 at 04:30 PM.
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01-17-2019, 05:12 PM
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Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,333
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Quote:
Originally Posted by Hartstoc
A big thank you to Ross- after reading Ross? post, I found this on the WalbroGSL395
It is a much better match to a180HP Lyc than the pumps shown in my first entry above, and draws 3A instead of 4.5A, so less heat to worry over, a much lower bypass ratio, and 50% greater range on battery power.
I?m holding my installation to a high standard of redundancy, so really intent upon the two pumps having separate electrical, switching, relief valves , and check valves external to the pump. I?m looking at keeping all of that hardware and adapting this pump to it instead.
Ya? gotta love VAF!- Otis
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This pump shows only about 22psi at 16 gph - why does that work for an O-360?
Also can someone explain why the 12 vs 13.5 volt graphs cross over in the 20 gph range? Either I'm missing something or that data is wrong.
__________________
Alex Peterson
RV6A N66AP 1700+ hours
KADC, Wadena, MN
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01-18-2019, 10:26 AM
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Join Date: Aug 2017
Location: Sebastopol,CA
Posts: 358
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Quote:
Originally Posted by AlexPeterson
This pump shows only about 22psi at 16 gph - why does that work for an O-360?
Also can someone explain why the 12 vs 13.5 volt graphs cross over in the 20 gph range? Either I'm missing something or that data is wrong.
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Alex- A couple of points about why this setup should work for my particular installation. First, note that these pumps are not expensive and there are higher- output Walbros that could easily be swapped out if experience proves me wrong. I?ll be setting up a good stoddard-solvent bench test for it and will do that swap-out before flying if the results are not satisfactory. I?ll also be in a position to answer your second question after this bench-testing(I?ve been wondering about that too! It also seems like 12V Amps should be higher than 13.5V Amps for a given output.).
The objective here is to end up with the most efficient single-pump operation in cruise so as to maximize range after an alternator failure, and to have an abundance of surplus when both pumps are operating. Efficiency is maximized partly by minimizing the rate of flow through the relief valve and back to the tank, as all energy used for that purpose is wasted.
My requirements in cruise range between 5.5 and 9 GPH at a target 24PSI, depending upon altitude, and my AP Bendix-type IO 360 is ok with as little as 20PSI. 7.5GPH at lower altitudes would be a lean, throttled-back economy cruise but still pretty fast and very doable. At higher altitudes I?m a big fan of LOP operation. In short, either of these pumps working alone should easily cover all of these reqirements, and significant but minimal fuel will still be flowing back to the tank.
Thanks to the fuel return lines I will be installing, either or both pumps can be operated with complete impunity any time the charging system is operating normally, and as needed to get out of a pinch even after an alternator failure. I?m pretty sure I have one of the most reliable alternator installations possible, but I should have 16-30AH of reserve battery capacity to work with if/when that happens. My minimum current draw with one pump and one Plasma III lightspeed operating will be under 6A, translating to a duration of between 2.7 and 5 hours with the G5 on integral backup minus a bit for occasional use of the remote com2 on the G3X. That will open up a big circle of real estate to choose from.
Clearly, this pump would not cut it as a good choice for this engine as a stand-alone, nor would it satisfy the needs of a higher pressure EFI system, but I?m betting it will be just right for my installation. I?ll be doing all TO/climb ops with both pumps operating, and the unlikely failure of one pump during such ops would be an event similar to the loss of one engine for a twin, but much easier to manage. Runnup will include veryfying fuel pressure at high power for each pump.
I?ll report back after I?ve done some bench testing on one, and if I reject it I?ll cut it up and show you the innards of that one!- Otis
__________________
Otis Holt-
RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2019 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"
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01-18-2019, 10:44 AM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,420
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Quote:
Originally Posted by Hartstoc
The objective here is to end up with the most efficient single-pump operation in cruise so as to maximize range after an alternator failure,
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Methinks you just described an engine driven mechanical pump.
__________________
Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011 
Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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01-18-2019, 11:04 AM
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Join Date: Nov 2005
Location: Davis, CA
Posts: 1,156
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max fuel flow
For what it's worth, I routinely see takeoff fuel flow numbers above 16 gph departing sea level airports (Sacramento Valley) even in hot weather. In cooler weather, above 17 gph. As measured with an EI red cube. My fuel flow numbers are unaffected by electric fuel pump operation. This has been consistent since the engine was new, currently at 740 hours. 180HP IO-360, P/A Silverhawk mechanical injection, constant speed prop.
__________________
Lars Pedersen
Davis, CA
RV-7 Flying as of June 24, 2012
960+ hours as of June 30, 2020. Where did the time go?
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01-18-2019, 11:14 AM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,297
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Quote:
Originally Posted by AlexPeterson
This pump shows only about 22psi at 16 gph - why does that work for an O-360?
Also can someone explain why the 12 vs 13.5 volt graphs cross over in the 20 gph range? Either I'm missing something or that data is wrong.
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The way these work is that they strive to achieve the the Pressure commanded by the regulator. You read the chart by looking at the PSI set by the regulator
then observe the flow rate at that PSI (e.g. x GPH @ y PSI). The pump will keep trying to deliver the PSI set by the regulator, all the way down to a 0 flow.
Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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01-18-2019, 11:38 AM
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Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
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Mike,
The only two things the stock pump has going for it are no-electrics-needed, and self-regulation. Downsides are multiple leak modes (some of which can effectively take out the boost pump with them) and vapor lock issues due to sucking on long supply lines in a hot environment.
Otis,
If you switch to the Walbro, most of the stuff in your original pic could be removed. No need for check valves; the pumps will not pass fuel in either direction when off. I don't see the need for more than one regulator, either, but if it makes you more comfortable, go for it.
And since you're already so far outside the box, a transfer pump & feeding the engine from one tank would mean you could eliminate the selector valve, too (again, the Walbro won't pass fuel unless it's running).
Ain't dominoes fun?
Charlie
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01-18-2019, 11:39 AM
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Join Date: Aug 2017
Location: Sebastopol,CA
Posts: 358
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Quote:
Originally Posted by Mike S
Methinks you just described an engine driven mechanical pump.
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Well, however reliable the engine driven pump may be, I think getting rid of it is a noble goal, and my abundance of battery power, initially triggered by the dual lightspeeds, makes that possible. In addition to the nasty set of potential failure modes described a few posts back, the engine driven pump adds a lot of flammable plumbing and fittings ahead of the firewall, and it could equally well be described as a brialliantly designed fuel heater, especially after shutdown on a hot day when all fuel within it and the nearby lines can vaporrize completely.
Consider the simplicity my firewall forward package. There will be one short firesleeved flexible #6 teflon lined hose connecting a stainless steel bulkhead fitting to the AP fuel metering valve, One longer teflon lined firesleeved #4 hose routed along a low-heat pathway to the flow divider, and the four solid stainless spider lines to the injectors. Four flair fittings total. Vaporization of fuel in these two flexible lines after will probably never happen, and their total internal volume is small, so hot starts should be very begnign. The pressure transducer, the fuel flow transducer, and the pumps themelves will all reside in the cool, low-vibration environment along the cabin floor? Sweet!!- Otis
__________________
Otis Holt-
RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2019 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"
Last edited by Hartstoc : 01-18-2019 at 11:44 AM.
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01-18-2019, 12:10 PM
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Join Date: Aug 2017
Location: Sebastopol,CA
Posts: 358
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Quote:
Originally Posted by rv7charlie
Mike,
The only two things the stock pump has going for it are no-electrics-needed, and self-regulation. Downsides are multiple leak modes (some of which can effectively take out the boost pump with them) and vapor lock issues due to sucking on long supply lines in a hot environment.
Otis,
If you switch to the Walbro, most of the stuff in your original pic could be removed. No need for check valves; the pumps will not pass fuel in either direction when off. I don't see the need for more than one regulator, either, but if it makes you more comfortable, go for it.
And since you're already so far outside the box, a transfer pump & feeding the engine from one tank would mean you could eliminate the selector valve, too (again, the Walbro won't pass fuel unless it's running).
Ain't dominoes fun?
Charlie
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Charlie, what you say is true, but in order to meet my very high standard of redundancy, I will use most of the hardware shown. I think it is too likely that the tiny checkvalves integral to these pumps could become lodged open by debris resulting from a pump failure, allowing reverse flow when pump #2 is engaged, so I’ll be using the big industrial duty external ones shown, which also serve as debris-dams from a failed pump. I do not need a regulator as such because the Bendix type metering valve is happy anywhere between 20 and 90 PSI, so each pump will have its own ground-adjustible relief valve dialed to 24PSI. A stuck relief valve, as someone brought up here, would by overridden by simply switching to the other pump. Btw there is a lot of built-in resistance to flow in these pumps, but some fuel can be forced through them in the absence of a check valve, possibly a lot depending upon the nature of the failure.
As you say, I’m going out of the traditional box, but I’m also quite conservative in my choices. For example, I’m big into technology, but I’ve got a personal rule against relying upon software and firmware for essential systems. So, I forego the advantages of EFI, programmable ignition systems, and software based control of essential electrical supply. Thus the lightspeeds, the Bendix type FI, and the use of old fashioned breakers and switches for essential loads.
I’m really loving all of the input and discussion here- thank you all! The advent of good, reliable lithium batteries has opened up a new world of possibilities for us, and it is a pleasure to be in on the ground floor of finding ways to discover and take advantage of them.- Otis
__________________
Otis Holt-
RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2019 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"
Last edited by Hartstoc : 01-18-2019 at 12:31 PM.
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01-18-2019, 12:15 PM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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Quote:
Originally Posted by lr172
The way these work is that they strive to achieve the the Pressure commanded by the regulator. You read the chart by looking at the PSI set by the regulator
then observe the flow rate at that PSI (e.g. x GPH @ y PSI). The pump will keep trying to deliver the PSI set by the regulator, all the way down to a 0 flow.
Larry
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These are positive displacement pumps and they put out the same volume of fuel all the time at a constant voltage. The regulator only modulates return flow to maintain the set fuel pressure which in most EFI systems is determined by MAP vs spring pressure and the volume of fuel the engine is consuming.
The pump isn't striving to do anything. It just runs. When return flow reaches zero, the regulator can do no more to maintain fuel pressure as the engine is burning 100% of the fuel the pump can deliver. Any more flow demand from the engine will result in lower fuel pressure and the AFR will start leaning out.
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