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Test Data!!!- Anatomy of a fuel pump, part 3-

Hartstoc

Well Known Member
Now that we are getting comfortable flying “electron-dependent” aircraft and have powerful, lightweight lithium batteries at our disposal, I’ve been thinking it is time to find a way to SAFELY eliminate one of the last vestiges of the magneto era- the engine driven mechanical fuel pump. There are a lot of really good reasons for doing this that I won’t go into here, but the challenge in making it possible is to find a reliable electric fuel pump properly matched to the task. This thread documents my successful search supported by real data, and I’ve generated accurate performance charts under real-world conditions for three pumps.

Thousands of airplanes already sport electric boost pumps that seem to work well, but on close examination few of them make any sense at all in this context.Two problems with most pumps currently in use is that they generate flow and consume power FAR IN EXCESS of our needs, and many feature continuous short-loop recirculation of the vast majority of their output back to the pump inlet. This is no big deal for backup pumps used intermittently, but wholly ill-suited to continuous operation in a twin-pump setup with no engine driven pump. Some are also quite heavy, bad news with two installed. For continuous operation, return lines to the tank in use become mandatory, and the pump must operate efficiently to minimize electrical demand in normal operation and maximize range on battery power should the alternator fail.

A plethora of choices exist in the 500-1,000 HP range for auto racing applications, but precious few really make sense in the context of typical RV’s. Also, I’ve discovered that published performance data for pumps is often not detailed, accurate, and reliable enough to allow intelligent selection, and these do not take into account system-wide resistance that must be subtracted from the performance of the unrestricted pump.

I decided to build this test rig, shown here collecting data for one of the Walbro pumps. It incorporates pre- and post-pump filters and enough lift, bends, turns, and manifold reversals to roughly mimic the aft-of-firewall dynamic flow restrictions of a typical RV installation. Here, the return line is closed off, and “engine” output, dialed-in at 30PSI resistance, is being shunted to the flow-measuring vessel.

2v2EpmY6TxBELK5.jpg


Here you can see the right side valve shunting output to the measuring vessel. The black marks were established using a precision flask, and the flow would be fully stabilized by the time the stopwatch was started at the bottom mark.

2v2EpmYsLxBELK5.jpg


I did thorough dynamic testing of three pumps and used the raw data to generate the three Excel performance charts below, testing each pump at 10PSI intervals from 0-60PSI(increased to 5PSI intervals within my operating range of 20-40PSI). The rig allows precise stopwatch timing of exactly one gallon of fluid at each pressure point. It features 3-way valves to shunt the output return line flow and/or “engine” flow into a measuring vessel or back to the source tank. The return line output was blocked completely for GPH vs. Pressure testing, but I also measured pressure and return-line GPH for each pump with the “engine” flow blocked completely to mimic pre-start operation of the pump.

My system will be Bendix-type FI from Airflow Performance, tolerant of wide swings in system pressure, so each pump on my RV will be equipped with simple external pressure-relief valves outputting to return lines(instead of a more sophisticated pressure regulators needed for EFI) and large external check valves, so the rig features those as well. I’ll say more about my experience with the very interesting dynamic behavior of these relief valves in a later post in this thread. Stoddard solvent, a form of mineral sprits, is generally used as a safer alternative to gasoline for these tests, but I went a step further and found an even safer soy-based solvent substitute. After Collecting complete data for all three pumps using this solvent, which has a similar viscosity to diesel fuel, did a carefully grounded calibration run with gasoline on the winning pump at 30PSI to validate my results. Somewhat shocked by the increased flows with gasoline, I ended up repeating the entire test series for the winning pump using gasoline(while constantly purging the airspace in both vessels with Argon!). You will see two output curves for each pump, the lower for the solvent tests, and the upper for gasoline. For the top chart, every data point on all curves was collected directly. For the bottom pump, I did three data points with Gasoline and saw the same relationship as with the first, and was able to derive correction criteria for the remaining points on the gasoline curve. For the middle chart, the entire gasoline curve was generated using correction criteria.

Finally, I decided to dismantle each pump tested to compare design and construction- some photos and discussion will follow in a later post in this thread.(edit note 2-17-19: I tried to add this info here but exceeded the allowable post word-count. Please see the post on page three of this thread where I’ve added photos and commentary- O.H.)

Happily, a very clear winner emerged for RV’s between 125 and 300HP, the Walbro GSL414, with results shown in the first graph. Note that it generates a reliable flow of more than 35GPH at all pressures below 40PSI, and consumes less than [email protected] through the 25-35PSI range that my RV will operate within. Even this output is far in excess of our needs up to about 300HP, but power required is so low that ONE of my twin EarthX ETX900-VNT’s will operate one of these pumps and a LightSpeed PlasmaIII through an entire 40-gallon fuel load!

Compare that with the absurdly high output and consumption of the Delphi from AP depicted in the third graph. All that surplus output pumped back through the return lines is wasted energy. At 795grams, the all-steel Deplhi also weighs nearly twice as much as the 454gram aluminum-body Walbro GSL’s.

I already feel well rewarded for the effort and dollars invested in this study, and I hope some of you find it useful as well.- Otis
And the winner is!: the Walbro GSL414
This pump pushes [email protected] through the return lines drawing [email protected] sitting idle at pre-start!

2v2EpmYk4xBELK5.jpg


The Walbro GSL395 was also tested, but proved less efficient.

2v2EpmYDTxBELK5.jpg


Here are results from the Delphi pump obtained from AP:
Pushes fully 62GPH@33 PSI drawing 4.2Amps @13.2V sitting idle pre-start. The flow from this pump was actually frightening to witness with gasoline.

2v2EpmYCWxBELK5.jpg


This is getting long, so I’ll save photos and discussion of the disassembled pumps for a later post in this thread.

Notes: the ammeter used was placed in series with my trusty Flukemeter, and reported parallel to #but 1/0th of an Amp lower than the Fluke across a 1-6Amp range. Voltage agrees perfectly.

Here iare links to parts one and two of this series:
http://www.vansairforce.com/community/showthread.php?t=167848&highlight=Anatomy
http://www.vansairforce.com/community/showthread.php?t=167848&highlight=Anatomy

Finally, I want to thank Ross Farnham at SDS for suggesting the GSL414 and for serving as my sounding board in many emails during this work-
 
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Otis, this is valuable work! Thank you.

Have you looked at reverse flow possibility in Walboro pumps? I am not familiar with their design. Is reverse flow a possible failure mode? Should an external check valve be installed or not needed?
 
Otis, this is valuable work! Thank you.

Have you looked at reverse flow possibility in Walboro pumps? I am not familiar with their design. Is reverse flow a possible failure mode? Should an external check valve be installed or not needed?

Nota problem, each pump has a tiny check valve at the outlet. My installation will include a big external check valve for each pump like the one just to the left of the pressure guage on my rig. My concern is that a pump failure could generate enough debris to block the tiny valve ooen, so this will be prevented by the external industrial duty check valve.
 
Thank you for your efforts. I'll confess to having been a bit skeptical about whether your efforts would be worth the trouble; clearly they were, to the benefit of many of us. I'm thinking about eventually dumping my mechanical pump as well, and though I have plenty of electrons available I might as well select for the most efficiency.

Question: where did you obtain the GSL414? A quick search makes it appear that they are somewhat rare. Amazon's site claims to have them but for some reason they claim that "this item cannot be shipped to your selected location." Also couldn't find anything on TI Automotive's website. I would be a little concerned about developing a fuel system around a part, or parts, that prove to be unicorns. Having been bitten by that in the best.
 
Thank you for your efforts. I'll confess to having been a bit skeptical about whether your efforts would be worth the trouble; clearly they were, to the benefit of many of us. I'm thinking about eventually dumping my mechanical pump as well, and though I have plenty of electrons available I might as well select for the most efficiency.

Question: where did you obtain the GSL414? A quick search makes it appear that they are somewhat rare. Amazon's site claims to have them but for some reason they claim that "this item cannot be shipped to your selected location." Also couldn't find anything on TI Automotive's website. I would be a little concerned about developing a fuel system around a part, or parts, that prove to be unicorns. Having been bitten by that in the best.

Thanks for the compliment! True the 414 is a bit rarer and a bit more expensive than the others($100-130) but they are out there. I believe you can obtain one from SDS
 
Bravo,

Yes, Bravo, Otis. First for your time and $ investment in understanding what you need, and second for validation of what the pumps will really do.

This kind of work when going off plan is needed to ensure the safety of the final product. Sharing it for others leverages the work for others to use.

Keep up the good work!
 
Thanks Otis, what is the part number/ manufacturer of that check valve?

I beieve they are made in house by Airflow Performance, ditto for the return valves and the nifty banjo-fitting manifold to which the relief valve in the photos is attached. Talk to Don Rivera there, everything they to is to the highest standard, yet generally light in weight. For full redundancy in a dual-pump system, each pump should ideally have its own external relief valve or regulator and its own external check valve. You don’t want the failure of one pump to be able to impact operation of the other one.- O
 
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A couple of notes-

1-Beware of counterfiet Walbro pumps- they are copied right down to the labels in China. Cyberspace Automotive Performance, one dealer offering them online has actually published an offer from a Chinese company to offer the fake pumps to their company! They supplied the Walbro’s I used for my testing, and are associated with TI Automotive.

You can also count on pumps offered by Ross Farnham at SDS being genuine products.

2- I’ll be keeping this test rig for a while, so if anyone has a pump that can be set up with an an-6 flaired inlet and a 12mm male banjo outlet is welcome to send it to me for flow testing- no charge just pay two-way shipping. I’d love to do the Walbro GSL392 and GSL393.- Otis
 
I might be completely off topic... but if I recall correctly, the Rotax 912iS uses dual electric fuel pump without a mechanical backup.

They seem to run very reliably...

Anyone know if they could be run on something else than a Rotax?
 
I might be completely off topic... but if I recall correctly, the Rotax 912iS uses dual electric fuel pump without a mechanical backup.

They seem to run very reliably...

Anyone know if they could be run on something else than a Rotax?

There are several RV's flying now with dual electric pumps and no mechanical backup, mine included.
 
There are several RV's flying now with dual electric pumps and no mechanical backup, mine included.

Understood- I assume that most running EFI rely on electric pumps(and how long has it been since ANY cars were built with mechanical pumps?!) My objective here is to encourage matching the pump to the job in a smart way, and to make the point that most installed pumps now amount to absurd overkill-wasting way too many electrons needlessly pumping fuel around in circles. Even the GSL414 has nearly a 2X output margin for a 180HP Lyc., and I?ll have two of them that could be operated simultaneously with impunity! With one operating, I will be drawing 2Amps in cruise instead of 4-5, and that is a big deal if you find yourself operating on battery power alone. With the right pump, that number could probably be brought down to 1.5 Amps, but I?m fine with 2A!-Otis
 
Yup, but according to your signature, you should drop dead any minute now ;)

I got told that so many times while building my airplane, I finally just owned it and put it in my signature. So far I'm stubbornly disappointing a lot of people.
 
There are several RV's flying now with dual electric pumps and no mechanical backup, mine included.

Hundreds in fact...

EFI is a bit different beast since we run 45-50 psi so delivery drops off a bit. We do want to move fuel through the pumps to keep the motor cool at all times too. Finally, with all associated plumbing/ fittings in the system, don't expect to have the full rated flow. One thing more important than saving current is to have enough fuel pressure at full power so the engine doesn't lean out. A little extra pump capacity is better than shaving the margins too close.

For Bendix/ AFP FI with the much lower pressure, the 414 pumps makes good sense on under 200 hp engines.
 
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Hundreds in fact...

EFI is a bit different beast since we run 45-50 psi so delivery drops off a bit. We do want to move fuel through the pumps to keep the motor cool at all times too. Finally, with all associated plumbing/ fittings in the system, don't expect to have the full rated flow. One thing more important than saving current is to have enough fuel pressure at full power so the engine doesn't lean out. A little extra pump capacity is better than shaving the margins too close.

For Bendix/ AFP FI with the much lower pressure, the 414 pumps makes good sense on under 200 hp engines.

Ross- You bring up a good point, it is important to verify that fuel delivery meets real-world need, with a comfortable margin, AT the injector. These Walbro pumps are customized internally for various pressure and flow profiles by altering gerotor thickness, port design, armature windings, and other factors.

I do think my limted investigation documented here indicates that the GSL414 could handle more HP in applications up to 50 PSI than you are suggesting, as it can push 34GPH of gasoline into 50PSI of resistance, and that is on my ttest rig that incorprates much of the resistance inherent in an RV installation(that is why the lowest data point is 1.5PSI instead of zero), but this should be verified on the ground for each installation.

The most imortant point I want to make is that properly matching the pump to each installation will reward the builder with minimal continuous power draw that will make life easier for the alternator, and maximal range on battery power that can save your butt in a pinch. Just throwing a monster pump on the plane and letting it pump vast quantities of fuel back to the tank is not smart design. Working pressure needs to be within the pump’s design “sweet-spot”, but excessive flow is nothing more than a waste of electrons.

Another important thing to consider is that, with a well designed, fully redundant dual-pump system, both pumps can be operated simultaneously with impunity. A single pump should be able to provide for high-power operations should one pump fail, but the margin of surplus need not be large. - Otis
 
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Reading this thread gave me an idea: some (most?) modern cars use variable speed pumps instead of bypass regulators to regulate fuel pressure. In the spirit of 'education/recreation', it would be pretty easy to make an Arduino-based fuel pump controller. Would use PID code driving a motor controller and a vane-type pump which is friendly to being PWM-driven.

Running a pump this way does away with all the bypass plumbing.

Oh, wait, they already make these things.
 
My objective here is to encourage matching the pump to the job in a smart way, and to make the point that most installed pumps now amount to absurd overkill-wasting way too many electrons needlessly pumping fuel around in circles.

Did a first class job of it too. Nice work.
 
Reading this thread gave me an idea: some (most?) modern cars use variable speed pumps instead of bypass regulators to regulate fuel pressure. In the spirit of 'education/recreation', it would be pretty easy to make an Arduino-based fuel pump controller. Would use PID code driving a motor controller and a vane-type pump which is friendly to being PWM-driven.

Running a pump this way does away with all the bypass plumbing.

Oh, wait, they already make these things.

Very do-able, if you're willing to use in-tank pumps. But for inline use, it'll be a problem. All the turbine pumps I've seen have two significant issues for inline use. They will not self-prime (no 'lift' ability), and their physical structure (specifically, the inlet) won't allow a direct hookup in an inline application.
 
Reading this thread gave me an idea: some (most?) modern cars use variable speed pumps instead of bypass regulators to regulate fuel pressure. In the spirit of 'education/recreation', it would be pretty easy to make an Arduino-based fuel pump controller. Would use PID code driving a motor controller and a vane-type pump which is friendly to being PWM-driven.

Running a pump this way does away with all the bypass plumbing.

Oh, wait, they already make these things.

Unfortunately if the pump dies, you lose the ability to get fuel from that tank.
 
The promised internals-

(2-17-19 edit) I promised to add photos and commentary on the internals of these pumps. Sorry for the delay- I’m putting this here for a “bump” , and also will try to edit it into the primary post of this thread.

Of the three pumps tested, I cut up the Walbro GSL395 and the Delphi, which are quite different internally. A Walbro tech told me that all of the GSL-series pumps would be very similar inside, with the differences being in gerotor thickness, motor windings, etc., so I decided to keep the GSL414 intact as a spare and for demo-ing my test rig at the next EAA chapter 124 meeting here in Santa Rosa, CA.

Major differences between the Walbro and the Delphi, which is OEM on several autos, include an all-steel outer body on the Delphi that is more than 1/10” thick to allow machining in stop-recesses at both ends. It also has plastic inlet and outlet bodies as compared with an integral aluminum inlet and housing and a precision machined cast aluminum outlet on the Walbro. The steel shell contributes to the huge difference in weight (795GM vs. 454GM).

The most significant differences lie within the pump section itself. The first two photos here are from the Delphi pump, which is a screwed -together sub assembly as seen in the top photo. With the cover removed you can see the roller vanes captured within a wheel directly driven off a set of five plastic fingers mounted to the end of the motor armature. Centrifugal force keeps the rollers in contact with the fixed, eccentric outer ring, so volume of the cavities between rollers grows and diminshes with each revolution.

2v2EpmY8hxBELK5.jpg

2v2EpmYNTxBELK5.jpg


The following shots show the Walbro GSL395 outer aluminum housing and thin-walled steel inner housing that carries two permanent magnets inside. The white plastic body to the left houses a fine, full cross-section filter screen and a relief valve for internally recirculating pump output back to the pump inlet in the event that output is locked. The Delphi is absent both of these features.This relief valve should never operate in normal operation of a proper installation. The screen is NOT serviceable, suggesting that a low-resistance, large-section, screened pre-filter should be used(Walbro recommends 40 microns). Note the beautiffuly machined outlet interior housing a tiny check valve. Both pumps feature check valves at the outlet, but I’d be concerned that this could be blocked open by debris during a failure, possibly robbing output from pump #2, so Iwill install big external check valves isolating each pump.

The second photo details the gerotor, a marvel of simplicity that has a very reassuring feel when rotated manually. The inner and outer gear profiles are ingenuously ground so that each lobe maintains precise contact with its mate at all times, creating sealed cavities that grow and shrink in volume when rotated. With this design, the inner gear is concentric and also directly driven by four plastic fingers at the end of the armature. The outer ring is driven by the inner gear to rotate within an offset bushing, made of a black composite material. Note that the inner gear has eight teeth and the outer gear nine, and the geimetry is such that with each revolution of the inner gear, the teeth progress by one tooth on the outer gear- brilliant!

2v2EpmYGVxBELK5.jpg


2v2EpmYFLxBELK5.jpg


Photos of the Chinese-made Airtex pump that I disassembled for an earlier thread, similar in design to the Delphi, can be seen here:
https://public.fotki.com/Hartstoc/anatomy-of-a-fuel-pump/
 
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Reading this thread gave me an idea: some (most?) modern cars use variable speed pumps instead of bypass regulators to regulate fuel pressure. In the spirit of 'education/recreation', it would be pretty easy to make an Arduino-based fuel pump controller. Would use PID code driving a motor controller and a vane-type pump which is friendly to being PWM-driven.

Running a pump this way does away with all the bypass plumbing.

Oh, wait, they already make these things.

I think you may have hit on an idea that could truely optimize power consumption! There IS a concern that throughput be adequate for pump cooling, but of course heat is proportional to current, so???. In deference to the KISS principle, I?ll leave that project to others and stick with the return lines and accept the full 2-2.5Amp current flow!- Otis
 
Hi All
I'm curious if anyone has actually directly plumbed the output of the GSL414 into a traditional mechanical fuel injection controller/servo. Because, it looks to me like this pump would easily over-pressure the controller/servo at a low flow rate and full 12v power. It looks like you'd still need a pressure regulator set to ~25 psi.

That said, I have a full arduino-based smart pump control reading Dynon data that runs the engine just fine (GLS395 and 0.022 nozzles) nearly full-range without any other fuel control hardware in the mix. It's a hobbyist project right now, but I'm looking to change out that pump.

The apparent advantage of the GLS395 is that the internal relief is set low enough to allow zero flow at modest pressure.
Bob
 
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Hi All
I'm curious if anyone has actually directly plumbed the output of the GSL414 into a traditional mechanical fuel injection controller/servo. Because, it looks to me like this pump would easily over-pressure the controller/servo at a low flow rate and full 12v power. It looks like you'd still need a pressure regulator set to ~25 psi.

That said, I have a full arduino-based smart pump control reading Dynon data that runs the engine just fine (GLS395 and 0.022 nozzles) nearly full-range without any other fuel control hardware in the mix. It's a hobbyist project right now, but I'm looking to change out that pump.



The apparent advantage of the GLS395 is that the internal relief is set low enough to allow zero flow at modest pressure.
Bob

Bob- all of these electric pumps are constant displacement, pumping between 35 and 80 GPH into a 30 psi load, so they require either a spring loaded relief valve or a regulator to maintain pressure. Bendix-type servos tolerate a fairly wide range of pressures so the spring type relief valves work fine, ideally set up to maintain about 30 psi at the servo. The vast majority of the fuel will always pass through the relief valve, and it is highly recommended that this fuel is directed back to the tank from which it came. Unfortunately, most aircraft are set up to re-circulate this fuel back to the pump inlet, which is a really BAD idea. The photos below are top and side views of the dual GSL414 system I built for my RV, which now has about 50 hours of flawless operation. I completely removed the engine driven fuel pump, and these new pumps are a fully redundant, mutually independent, parallel system, each with access to two independent power sources. Note the dual Andair fuel selector valve, the top level of which receives fuel from the relief valves and returns it to the selected tank. Also note that the fuel flow and pressure reducers, as well as two large inline filters are part of this package, which resides at the bottom of my center console. Finally, note the industrial-duty check valves on where the pressurized fuel feeds into the manifold feeding fuel to the engine. The pumps themselves have built-in check valves to prevent reverse flow, but they are tiny. The concern is that debris from a failed pump could block them in the open position, allowing the backup pump to reverse-flow fuel through the failed pump. The big check valves prevent this possibility. I’ll be expanding on all of this in future posts.- Otis

2v2aBjJ3gxBELK5.jpg


2v2aBjuGnxBELK5.jpg
 
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Wow, that's a lot of gear and thoughtfully, if rigidly, assembled. Glad you were at least able to remove the mechanical pump.

re: internal relief.. You're right that high-powered (above 100W) pumps shouldn't just circulate to the pump inlet. The GSL395 at a regulated 10v will only dissipate about 25 W, and even a flow rate of just 2 GPH will only result in a 5 F temperature rise of the fuel. At lowest cruise power like 6 GPH, temp rise is negligible. That's the beauty of these low-power (high resistance wound) pumps. Even at likely full voltage, the power is only 48 W, still just a 10 F rise minus heat dissipated externally.

I'd be plenty comfortable with the built-in check valves for simplicity, since the pump also has a screen, but to each their own. A hard piece of debris causes a larger leak in a larger valve that doesn't close, versus a smaller one.

Anyway, glad that complex assembly is working for you. Thanks for sharing all the information!
 
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Wow, that's a lot of gear and thoughtfully, if rigidly, assembled. Glad you were at least able to remove the mechanical pump.

re: internal relief.. You're right that high-powered (above 100W) pumps shouldn't just circulate to the pump inlet. The GSL395 at a regulated 10v will only dissipate about 25 W, and even a flow rate of just 2 GPH will only result in a 5 F temperature rise of the fuel. At lowest cruise power like 6 GPH, temp rise is negligible. That's the beauty of these low-power (high resistance wound) pumps. Even at likely full voltage, the power is only 48 W, still just a 10 F rise minus heat dissipated externally.

I'd be plenty comfortable with the built-in check valves for simplicity, since the pump also has a screen, but to each their own. A hard piece of debris causes a larger leak in a larger valve that doesn't close, versus a smaller one.

Anyway, glad that complex assembly is working for you. Thanks for sharing all the information!

Thanks for your insights- A couple of comments in response:
-The concern about short loop re-circulation back to the pump inlet is more serious than you suggest. While you are correct about heat added being proportional to pump wattage, temperature rise is a function of fuel throughput. When throughput is low, heat is added with each cycle, and temperature can very easily rise to the boiling point. The classic scenario is forgetting to turn off the boost pump, and executing a long descent to destination at very low power, with throughput of just a couple of gallons per hour. If the pump is displacing 60 GPH, imagine the cycle rate through a 6” return to inlet loop! These pumps don’t pump vapor, so you could be in for a nasty surprise if you find yourself in need of power for a go-around or glide slope adjustment on final. My system is actually fuel-cooled, as all surplus flow is injected back into the tank it came from right at the wing leading edge, and the pump inlet receives only super-cool fuel directly from the tank.
- any debris ejected during a pump failure is far more likely to make it past the large check valve than the miniscule one built into the pump outlet, where it would be harmlessly captured by the gigantic 40 micron filter ahead of the fuel flow transducer in my system. Nothing making it past the tiny one is likely to end up blocking the big one open.- Otis
 
GSL414 decreasing performance

After running the engine for perhaps 70 hours and flying 40 hours of that I found that the GSL414 dropped in performance.

The reason I picked the GSL414 was the much lesser current draw (3 amps) compared to the GSL393 (about10 amps). Seemed a waste to pump most of the fuel back to the tank through the fuel regulator with the bigger GSL393 pump. Important if alternator fails -- will get you further on the battery before engine quits.

However it now seems that the Walbro GSL pumps loose efficiency (pressure/flow) over time (also have reports of the GSL391/2/3) "going bad" -- increased amperage and decreased flow.

So keep this in mind when choosing your EFI pump and keep an eye on fuel pressure. Kind of unnerving when applying throttle and engine stumbles, checking mixture (if you have an oxygen sensor) finding it way lean and finally seeing low fuel pressure.

Note that I have a GSL393 as my backup pump.

Finn
 
After running the engine for perhaps 70 hours and flying 40 hours of that I found that the GSL414 dropped in performance.

The reason I picked the GSL414 was the much lesser current draw (3 amps) compared to the GSL393 (about10 amps). Seemed a waste to pump most of the fuel back to the tank through the fuel regulator with the bigger GSL393 pump. Important if alternator fails -- will get you further on the battery before engine quits.

However it now seems that the Walbro GSL pumps loose efficiency (pressure/flow) over time (also have reports of the GSL391/2/3) "going bad" -- increased amperage and decreased flow.

So keep this in mind when choosing your EFI pump and keep an eye on fuel pressure. Kind of unnerving when applying throttle and engine stumbles, checking mixture (if you have an oxygen sensor) finding it way lean and finally seeing low fuel pressure.

Note that I have a GSL393 as my backup pump.

Finn

Interesting. That type of pump has very linear characteristics. The only real scenario that makes sense for what you describe is a mechanical failure where the pump's internal friction has drastically increased.

I'd check your BPR while you're at it. This may be the result of not bypassing enough fuel through it. If you can determine the BPR' min and max flow requirements, we could verify proper sizing. What is the required fuel system pressure for this engine?
 
Interesting. That type of pump has very linear characteristics. The only real scenario that makes sense for what you describe is a mechanical failure where the pump's internal friction has drastically increased.

I'd check your BPR while you're at it. This may be the result of not bypassing enough fuel through it. If you can determine the BPR' min and max flow requirements, we could verify proper sizing. What is the required fuel system pressure for this engine?

Yes, the fuel pressure regulator was a suspect. However, after replacing the GSL414 with a new one, the pressure stayed up during this mornings test flight. I should mention that the pressure would gradually drop during flights and also over the hours of use. On the ground with engine not running, the pressure was OK. I set the regulator to about 37 psi. I can compensate for pressure changes with the engine controller's mixture control. In previous recent flights, seeing as low as 24 psi, I turned on the GSL393 and off the (bad?) GSL414 and pressure was back to normal.

With the new GSL414 I see 42 psi (engine not running) and 43 psi with the GSL393.

Note that my pressure sender is at the very end of the fuel rail and have fine EFI filter between regulator and fuel rail.

Finn
 
After running the engine for perhaps 70 hours and flying 40 hours of that I found that the GSL414 dropped in performance.

The reason I picked the GSL414 was the much lesser current draw (3 amps) compared to the GSL393 (about10 amps). Seemed a waste to pump most of the fuel back to the tank through the fuel regulator with the bigger GSL393 pump. Important if alternator fails -- will get you further on the battery before engine quits.

However it now seems that the Walbro GSL pumps loose efficiency (pressure/flow) over time (also have reports of the GSL391/2/3) "going bad" -- increased amperage and decreased flow.

So keep this in mind when choosing your EFI pump and keep an eye on fuel pressure. Kind of unnerving when applying throttle and engine stumbles, checking mixture (if you have an oxygen sensor) finding it way lean and finally seeing low fuel pressure.

Note that I have a GSL393 as my backup pump.

Finn

I've run a 392 for over 5000 hours in our turbo shop car. Never touched, still working fine and producing enough volume and pressure to feed 275hp.

I have many dozens of customers with over 500 hours on their pumps, several with over 800.

A 393 should be drawing around 5.5 amps at 43.5 psi, not 10.

The biggest killer of these appears to be air entering the inlet or improper mounting- never with inlet facing above horizontal. Seen 2 die in less than 3 hours when these things are present.

Out of around 900 pumps sold, have now seen 6 go bad. 4 from improper mounting and/or restricted flow or entrained air. 2 unknown causes.

We supply 414s for engines under 150hp, 393s for engines up to 300hp and 392s for engines up to 400hp.
 
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I've run a 392 for over 5000 hours in our turbo shop car. Never touched, still working fine and producing enough volume and pressure to feed 275hp.

I have many dozens of customers with over 500 hours on their pumps, several with over 800.

A 393 should be drawing around 5.5 amps at 43.5 psi, not 10.

The biggest killer of these appears to be air entering the inlet or improper mounting- never with inlet facing above horizontal. Seen 2 die in less than 3 hours when these things are present.

Out of around 900 pumps sold, have now seen 6 go bad. 4 from improper mounting and/or restricted flow or entrained air. 2 unknown causes.

We supply 414s for engines under 150hp, 393s for engines up to 300hp and 392s for engines up to 400hp.

Thanks Ross.

I was not aware of mounting requirements.
Please clarify.
Is the inlet supposed to be above outlet? Mine is slightly below in level flight, more so with tail down. (Most of running has been tail down during engine ground runs for testing.) Sits about 1" above floor, right side, just front of main spar in the RV-4, so with 5 gals or more in the tank, inlet should be flooded, once pickup and pre-pump filter is filled -- a couple of seconds?

If I were to build the right tank again, I would use a finger strainer in lower back corner instead of the standard pickup that goes up about 3".

Because I'm over propped I'm not seeing more than 13 GPH. Figured the 414 be good up to 180 HP or 15 GPH. Not expecting to use more than 8 GPH in cruise. Just brief full power take-off, then pull back to 10 GPH in initial climb from pattern altitude and then 6 - 8 GPH in cruise.

Need to actually measure the 393's current draw. The 10 amps was from memory -- could have been confusing it with 392 or 391.

Finn
 

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Discharge should to be level or higher than inlet.

Flooded inlet is safest and gives the least chance of vapor lock with Mogas, hot day, high altitude.

If the pumps sound gravelly, they are on their way out or are sucking some air bubbles. Should be a smooth whirring noise when they happy. Good to take a listen before startup. Unusual noises are cause for investigation.
 
Yes, but

Discharge should to be level or higher than inlet.

Flooded inlet is safest and gives the least chance of vapor lock with Mogas, hot day, high altitude.

If the pumps sound gravelly, they are on their way out or are sucking some air bubbles. Should be a smooth whirring noise when they happy. Good to take a listen before startup. Unusual noises are cause for investigation.

All of this is obviously true; but, from the pic there's a downcomer line. Unless there's an air leak on the suction side, that config should be fine.

Obviously I don't have component info or data. I'm still not convinced the BPR and pump are optimally sized for each other. I base this on (assumed) measured amp draw alone. RPM-> flow and should be relatively flat over it's range. Amp draw ->pressure. This would infer 10 amps is required because the delivery pressure is almost double. This is why I suspect the BPR's travel range has been exceeded. This also assumes the instrument measurements are correct. Would be a fun one to troubleshoot.

After checking for air leaks (which could be inside a tank) and verifying instrumentation isn't lying to you, I'd still suggest getting any related component info you can and looking through it. Share it here if need be.
 
BPR?

I thought it was a typo and was FPR. What's BPR?

GSL393 pulls 6.67 amps (engine not running, all fuel returned to tank via fuel pressure regulator).

Fuel pressure regulator is a cheap knockoff. Had leak issues around mating parts (that also captures the membrane). Sanded mating surfaces flat and reassembled and no leaks.

But want to change over to use the Mazda RX-7 regulator. Lighter and has a reputation of not failing. But wanted to only change one thing at a time. Replacing the GSL414 with a new one brought pressure back up, so I assumed it was the problem. I really don't know how to check for air leaks.

Pumps sound fine to me, higher RPM when start up, then slow down a bit as pressure builds up.

Finn
 

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BPR isn't a term I'm familiar with but if your refer to the pressure regulator (usually abbreviated FPR), it doesn't care how much flow goes through it as long as not so excessive as to exceed its max flow rate to be able to control pressure properly. We sometimes see a 1-2 psi pressure rise with both pumps on as the regulator valve is full open, trying to bypass all that fuel back to the tank.

Since these are constant flow pumps, all the fuel passes through the pumps and that is important to keeping them cool. At full power, perhaps 50-75% is burned by the engine and 50-25% goes through the FPR. At idle, perhaps 1-2% is burned by the engine and 99-98% goes through the FPR and is returned to the tanks.

We've seen problems when people don't return fuel to the tanks for good heat sinking and de-aeration but return directly to the pump inlet. That's a bad idea as any entrained air is trapped in the system and can only process out through the injectors.

Restriction of the pump inlet with a partially plugged filter is bad news for the pump as well. Check these.

Also, not good to have the feed and return fittings too close together in the tanks where the feed can pick up air bubbles from the return. We can sometimes see entrained air when using clear tubing on the return line on our engine test stand and on customer aircraft when trouble shooting vapor lock or running issues, most recently on a Rotax 912 powered one. Return fitting should be above and away from feed fitting so entrained air can rise upwards and away from the feed.

It doesn't take much air to seriously reduce pump life and cause running issues. If you're pump life is short, I'd investigate the layout and routing of lines, fittings and pumps. The best success on low wing aircraft has been with the pumps flat on the floor, right below the selector with no 90 deg fittings prior to the inlet. 90 deg mandrel bent fittings are ok as we see here.

Once the fuel passes through the FPR, pressure goes down to near atmospheric so if the fuel is hot vapor bubbles can immediately form. They generally won't on the pressure side.

I alternate the pump used- pump 1 on odd days of the month, pump 2 on even days to split wear. We recommend replacing pumps if they sound weird or at 2000 hours for the pair (about 1000 hours each running time if you use my method).

Finally, there are at least 2 counterfeit makers of Walbro/TI pumps out there and these are complete junk, lucky to last 25 hours. Only buy from reputable sources.
 
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Thumb typing so pardon any brevity.

Pressure Regs are basically two types; the assumed application senses/controls downstream/forward pressure. One that senses/controls upstream pressure (like here) is a Back Pressure Reg.

They are typically force balanced off of system pressure (fuel here), a reference pressure (atmospheric is most common or sometimes manifold pressure for this app) and spring force.

Coil springs forces are only fairly linear over a short range so a psi or two change for different flows is common. If it gets compressed too far especially to solid height, the force goes through the roof quickly; subsequently pressure as well.

If your highest return system flow (engine off) to lowest (WOT) has a significant change in pressure, you’ve most certainly exceeded the BPR’s range. Size carefully and accordingly to the OEMs specs.
 
...
We've seen problems when people don't return fuel to the tanks for good heat sinking and de-aeration but return directly to the pump inlet. That's a bad idea as any entrained air is trapped in the system and can only process out through the injectors.
...

Finally, there are at least 2 counterfeit makers of Walbro/TI pumps out there and these are complete junk, lucky to last 25 hours. Only buy from reputable sources.

My return line goes at least out into the second bay, if not more.

This was where I bought the newest replacement pump. Hope it's not a bad source.

https://www.ebay.com/itm/273889020230

Finn
 
...
If your highest return system flow (engine off) to lowest (WOT) has a significant change in pressure, you’ve most certainly exceeded the BPR’s range. Size carefully and accordingly to the OEMs specs.

Checking datalog from last flight: 39 psi WOT take-off. 41 psi engine not running. Significant?

Finn
 
Not one bit. I thought you were having pressure excursions and decay from your previous posts. Something to keep an eye on.
 
Not one bit. I thought you were having pressure excursions and decay from your previous posts. Something to keep an eye on.

I was until I replaced the GSL414 pump with a new GSL414. Thus my first post to this thread as a warning about picking too small a pump due to potential pump degrade over time. Picking a bigger pump you won't see the degrade as fast (unless you actually measure flow through it) because it simply means less and less fuel is pumped back to the tank via the FPR, until it gets so bad that there is no excess fuel pumped at full throttle.

If course I could be completely wrong, pumping air, have a bad FPR, partially blocked filters or other issues.

Finn
 
Finally, there are at least 2 counterfeit makers of Walbro/TI pumps out there and these are complete junk, lucky to last 25 hours. Only buy from reputable sources.

Interesting, I was just looking on the Walbro website for another application and they listed a warning of counterfeits for certain models.
 
One can use a PWM driver to reduce power input and thereby the stress on the pump. One can connect the pump power feed through a dual pole dual throw switch where one position is with regulated input power and the second position is with full voltage direct from the DC bus.

Picture of a sample 200W PWM driver for just over $12
 

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With rare exception for specific models, the pump OEMs do not warrant and even prohibit PWM control of their products. Some control modules have better dampening than others but all increase torsional vibes to some degre. It may wind up being “OK” because the pump doesn’t fail immediately and a future point of anecdote but risk to reliability does increase. Proceed with caution
 
I have recently purchased the RV7A from Frank Hinde who used electric fuel pumps in the wing roots and no mechanical fuel pump. He built dual electrical systems (single battery) with 2 alternators. On my flight back from AZ, the right fuel pump failed on climb out from Levingston, TX. I was able to make it home to KNEW on the other tank with anxious thoughts. My suggestion is to allow access to either tank with both fuel pumps. My plane was set up with the fuel selector valve only serving as an on off switch and not right or left tank. I made it home and disassembled the system, purchased Vans plans and rebuilt the fuel system according to Vans original design. Installing the mechanical fuel pump was not the easiest part of the project. I am not against electric fuel pumps as an option, I have just experienced an issue with a flaw in the design of mine and wanted to share that with you. Great test information and good luck.
 
With rare exception for specific models, the pump OEMs do not warrant and even prohibit PWM control of their products. Some control modules have better dampening than others but all increase torsional vibes to some degre. It may wind up being “OK” because the pump doesn’t fail immediately and a future point of anecdote but risk to reliability does increase. Proceed with caution

Correct and good point. TI specifically says not to use PWM on the GSL series of pumps. They do make other pumps designed to work with PWM.
 
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