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  #51  
Old 01-18-2019, 04:15 PM
rv7charlie rv7charlie is offline
 
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Location: Pocahontas MS
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"ground-adjustible relief valve dialed to 24PSI"

In other words, a regulator. :-)

If it doesn't have something in it to set pressure (typically a spring) which applies pressure to a movable valve, it won't maintain a set pressure. A fixed orifice will result in varying pressure as fuel consumption changes, with flow going up when you want it decreasing, and decreasing when you want it going up.
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  #52  
Old 01-18-2019, 09:28 PM
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AlexPeterson AlexPeterson is offline
 
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Originally Posted by lr172 View Post
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
I'll be clearer: 22psi at a full throttle, sea level condition of an O360 (16-17 gph) is not adequate. Yes, the engine will run, but the engine driven fuel pump will deliver in the high 20's psi at that flow rate.

The second part of my question was the apparently incorrect or incorrectly obtained data by the manufacturer. The graphs of 12 and 13.5 volts should not cross, unless there is some new mystery to DC motors and constant displacement pumps that I've not heard of.
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  #53  
Old 01-19-2019, 08:40 AM
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Hartstoc Hartstoc is offline
 
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Quote:
Originally Posted by AlexPeterson View Post
I'll be clearer: 22psi at a full throttle, sea level condition of an O360 (16-17 gph) is not adequate. Yes, the engine will run, but the engine driven fuel pump will deliver in the high 20's psi at that flow rate.

The second part of my question was the apparently incorrect or incorrectly obtained data by the manufacturer. The graphs of 12 and 13.5 volts should not cross, unless there is some new mystery to DC motors and constant displacement pumps that I've not heard of.
Alex- I agree completely with everything you say here. With both pumps operating, which will be standard proceedure for TO&climb, I should have ample fuel flow with a huge surplus. I can also operate both pumps continuously anytime and for however long I wish, so would do so during aerobatics as an example. In fact, the only real reason for turning one off would be loss of the alternator, but I?ll probably run on one pump during cross country cruise just to lighten the load on the alternator a bit.

This installation will be analogous to dual mags- two for normal ops but one will get you by with a little judicious management. I would anticipate a similar rate of serious malfunction as well(quite rare). Just as with mag checks, runnups will include verfifcation that each pump is fully operational, and I would no more take off with one pump inop than I would ignore a bad mag check. The redundancy of this pair of pumps will also equal that of dual mags. Each pump will be powered through an on-off-on switch with direct, full-time access to either of the two essential loads busses, each of which will be hardwired to one of the twin batteries. Yes, you must turn off all pump and ignition switches as the essential loads busses will be ever-hot, but I have a good solution for insuring that.

The graph is from Walbro, and I agree that it does not make sense. I will be be doing extensive bench testing with Stoddard solvent before istalling this particular pump, and will report back with my own data. Thank you for your input!- Otis
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RV-7A (bought)
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RV-8A, S-7C, Europa, Glastar.
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  #54  
Old 01-19-2019, 10:48 AM
Lars Lars is offline
 
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Location: Davis, CA
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Originally Posted by Hartstoc View Post
Alex- I agree completely with everything you say here. With both pumps operating, which will be standard proceedure for TO&climb, I should have ample fuel flow with a huge surplus. I can also operate both pumps continuously anytime and for however long I wish, so would do so during aerobatics as an example. In fact, the only real reason for turning one off would be loss of the alternator, but I?ll probably run on one pump during cross country cruise just to lighten the load on the alternator a bit.

This installation will be analogous to dual mags- two for normal ops but one will get you by with a little judicious management. I would anticipate a similar rate of serious malfunction as well(quite rare). Just as with mag checks, runnups will include verfifcation that each pump is fully operational, and I would no more take off with one pump inop than I would ignore a bad mag check. The redundancy of this pair of pumps will also equal that of dual mags. Each pump will be powered through an on-off-on switch with direct, full-time access to either of the two essential loads busses, each of which will be hardwired to one of the twin batteries. Yes, you must turn off all pump and ignition switches as the essential loads busses will be ever-hot, but I have a good solution for insuring that.

The graph is from Walbro, and I agree that it does not make sense. I will be be doing extensive bench testing with Stoddard solvent before istalling this particular pump, and will report back with my own data. Thank you for your input!- Otis
My concern was the same as Alex's; that was why I posted my T/O numbers. This clarifies things.

Question: I presume the hexagonal cylinders on top of the pumps are the relief valves (or pressure regulators or..)? How does one set them? I'm familiar with external fuel pressure regulators from various automotive EFI projects over the years, for example: https://www.aeromotiveinc.com/produc...***-regulator/ but those remind me of a typical fixed-spring relief valve like one might see in industrial applications.

As for Airtex pumps, the E-2315 in my AFP pump assembly failed at about 650 hours of extremely intermittent use. I was surprised and disappointed. I have a Bosch external inline pump mounted inside the frame rail on my ground bound 4x4 that has been dead reliable for almost 20 years and 120,000 miles of abuse, mounted inside the frame rail and exposed (needlessly, I've been too lazy to move it) to a hot exhaust system and occasionally packed with mud (thus thermally insulated). Replaced with Walbro GSL393 which, as a bonus, is much quieter.
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  #55  
Old 01-21-2019, 07:26 PM
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Hartstoc Hartstoc is offline
 
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Quote:
Originally Posted by Lars View Post
My concern was the same as Alex's; that was why I posted my T/O numbers. This clarifies things.

Question: I presume the hexagonal cylinders on top of the pumps are the relief valves (or pressure regulators or..)? How does one set them? I'm familiar with external fuel pressure regulators from various automotive EFI projects over the years, for example: https://www.aeromotiveinc.com/produc...***-regulator/ but those remind me of a typical fixed-spring relief valve like one might see in industrial applications.

As for Airtex pumps, the E-2315 in my AFP pump assembly failed at about 650 hours of extremely intermittent use. I was surprised and disappointed. I have a Bosch external inline pump mounted inside the frame rail on my ground bound 4x4 that has been dead reliable for almost 20 years and 120,000 miles of abuse, mounted inside the frame rail and exposed (needlessly, I've been too lazy to move it) to a hot exhaust system and occasionally packed with mud (thus thermally insulated). Replaced with Walbro GSL393 which, as a bonus, is much quieter.
The relief valves can be fine tuned to a degree by shimming to compress the spring slightly, or shimming the cap to reduce spring pressure. Altering the length of the body or the spring can do the same. Swapping out different springs can produce larger adjustments, but Airflow performance relief valves can be expectedto be pretty darn close to target without modification.

I was told today by a Walbro tech that their pumps are NOT, in fact, roller vane but geared, which could explain their higher reliability and their superior self-priming ability. Within a few weeks I will be doing some extensive bench testing on the GSL395 to determine its suitability for Bendix-type FI systems in a dual pump installation, and I will autopsy that pump to verify what I was told today, so at some point there will be an”anatomy a fuel pump, part II” thread.

Btw- the Walbro tech agreed that the published graphs for GSL395 performance are flawed. For example, he looked at the raw data for the 20PSI pressure point, and verified that at 12V flow would be 29GPH but over 40GPH AT 13.5V. The graphs indicate anout 27GPH at 12V and just 19GpH @ 13.5V, which is absurd!

I won’t be bench testing any short-loop recirculation setups because I will be installing fuel return lines to my tanks, but I will heat the Stoddard solvent to 100°F as part of the testing to determine effects of absolute fuel temp on flow dynamics. If I determine that the GSL 395 is inadequate, The obvious choice wil lbe the more powerful, higher pressure GSL393. My ultimate objective is to find the most efficient suitable pump for my needs, with emphasis on range under battery power. Obviously, energy used to push fuel through a relief valve is wasted, so using a 100+PSI pump pushing 40GPM, such as the Delphi obtained from AP or the walbro GSL393 to fuel my 24PSI, <10GPM requirement at most times is contra-indicated. The concern about the GSL395 isthat flow drops off pretty precipitously below 30PSI, so I’ll be focusing upon the 25PSI data point. The Walbro rep did tell me that, if I find performance satisfactory, there would be no harm in operating the GSL395 continuously at 25PSI.- Otis
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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 : 01-22-2019 at 08:22 AM.
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  #56  
Old 01-21-2019, 07:30 PM
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rv6ejguy rv6ejguy is offline
 
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I'll try to find time to cut open this bad 393 I have here and post a photo. I'm curious about what's inside too.
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 441.0 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
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  #57  
Old 01-22-2019, 08:26 AM
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Hartstoc Hartstoc is offline
 
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Originally Posted by rv6ejguy View Post
I'll try to find time to cut open this bad 393 I have here and post a photo. I'm curious about what's inside too.
Ross- That would be most helpful- I was one of those kids who revelled in taking things apart to see how they work(or don?t), and still find that technique hard to beat!-Otis
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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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  #58  
Old 01-22-2019, 09:44 AM
rv7charlie rv7charlie is offline
 
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Quote:
Originally Posted by Hartstoc View Post
The relief valves can be fine tuned to a degree by shimming to compress the spring slightly, or shimming the cap to reduce spring pressure. Altering the length of the body or the spring can do the same. Swapping out different springs can produce larger adjustments, but Airflow performance relief valves can be expectedto be pretty darn close to target without modification.

I was told today by a Walbro tech that their pumps are NOT, in fact, roller vane but geared, which could explain their higher reliability and their superior self-priming ability. Within a few weeks I will be doing some extensive bench testing on the GSL395 to determine its suitability for Bendix-type FI systems in a dual pump installation, and I will autopsy that pump to verify what I was told today, so at some point there will be an?anatomy a fuel pump, part II? thread.

Btw- the Walbro tech agreed that the published graphs for GSL395 performance are flawed. For example, he looked at the raw data for the 20PSI pressure point, and verified that at 12V flow would be 29GPH but over 40GPH AT 13.5V. The graphs indicate anout 27GPH at 12V and just 19GpH @ 13.5V, which is absurd!

I won?t be bench testing any short-loop recirculation setups because I will be installing fuel return lines to my tanks, but I will heat the Stoddard solvent to 100?F as part of the testing to determine effects of absolute fuel temp on flow dynamics. If I determine that the GSL 395 is inadequate, The obvious choice wil lbe the more powerful, higher pressure GSL393. My ultimate objective is to find the most efficient suitable pump for my needs, with emphasis on range under battery power. Obviously, energy used to push fuel through a relief valve is wasted, so using a 100+PSI pump pushing 40GPM, such as the Delphi obtained from AP or the walbro GSL393 to fuel my 24PSI, <10GPM requirement at most times is contra-indicated. The concern about the GSL395 isthat flow drops off pretty precipitously below 30PSI, so I?ll be focusing upon the 25PSI data point. The Walbro rep did tell me that, if I find performance satisfactory, there would be no harm in operating the GSL395 continuously at 25PSI.- Otis
'geared' : Gerotor

Your statements about flow vs pressure seem to contradict reality. Given a non-changing supply voltage, a positive displacement pump's flow will not drop with reduced pressure; it will drop with increased pressure. As long as the pressure isn't above the pump's design point, the pump itself will flow at least the quantity of fuel shown in its ratings.

Charlie

http://www.pumpschool.com/principles/gerotor.asp
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  #59  
Old 01-22-2019, 11:02 AM
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Hartstoc Hartstoc is offline
 
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Quote:
Originally Posted by rv7charlie View Post
'geared' : Gerotor

Your statements about flow vs pressure seem to contradict reality. Given a non-changing supply voltage, a positive displacement pump's flow will not drop with reduced pressure; it will drop with increased pressure. As long as the pressure isn't above the pump's design point, the pump itself will flow at least the quantity of fuel shown in its ratings.

Charlie

http://www.pumpschool.com/principles/gerotor.asp
Charlie- I do not see anything I’ve suggested that contradicts what you are saying here, but I think I understand the confusion. I was referencing the erroneous nature of the performance chart published by Walbro for the GLS395. 30PSI is indeed where the flow falls to zero for this pump even at 13.5V, so my task is to insure that sufficient flow remains at 25PSI for my needs(with two operating in parallel for high-flow operations). If you go all the way down to 20PSI there is ample flow for my needs with even one pump, but I don’t want to push the Bendix- type fuel metering valve to its lower limit, so will target an operation pressure of 24PSI per AP instructions. Clearly, the GSL395, even two of them operating in parallel, would not suffice For any EFI system I am aware of.- Otis
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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 : 01-22-2019 at 11:18 AM.
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  #60  
Old 01-22-2019, 12:07 PM
rv7charlie rv7charlie is offline
 
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"The concern about the GSL395 is that flow drops off pretty precipitously below 30PSI" and related statements are what I was referring to.

Are you trying to say that it drops off as pressure *increases*, approaching 30 psi? The wording sounds like you're saying the opposite, and is reinforced with the statement following that it 'would be ok to operate at 25 psi'.

FWIW, I suspect that your best path to lower power consumption at needed flow would be to move to in-tank turbine pumps. The ones I've researched seem to have significantly lower current requirements than gerotor or roller-vane pumps for the same flow/pressure, and have the added bonus of being easily controlled with PWM, which others have mentioned. With PWM, power required varies with actual flow/pressure, so low engine power would require less pump power.

Charlie
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