Superduty

OK guys. Here is the next show stopper. Assuming that we use the same length of hose in each one of those scenarios (the shorter paths have some loops in them...) then the restriction in the system is the same for all of them, and the total pressure is the same for all of them and thus the fuel flow is the same for all of them.

And, while we are at it, I picked the plus 5 feet for the pump in the one scenario because that is a reasonable suction head for a lot of pumps.

Have you ever siphoned fuel out of a fuel tank ? How does that work ?

Superduty

Lets say we have a tank at elevation zero. And we have a solid fence next to it. And we want to siphon some fluid out of the tank over the fence to a trench on the other side. And so we do.

Now, lets say we use the same hose. And we add our lift pump on the end (outlet) of the hose. How much pressure have we added to the system ? Answer: 12 PSI.

Now, lets say we use the same hose. And we add our lift pump to the start of the hose, over at the tank, on the other side of the fence. How much pressure have we added to the system ? Answer: 12 PSI.

The flow rate in both of the lift pump cases is the same.

CAVEAT: the lift pump in the first case may be getting close to cavitating depending on the length and suction of the line because the absolute pressure at its inlet could be as low as 14.7PSI -12 PSI = 2.7 PSIA. (I'm simplifying here...) If there was some restriction on its outlet (like a VP44 or a fuel filter) then it wouldn't be prone to cavitating.

Superduty

Here is a question for you guys that relocated your lift pump and happened to see the pressure increase. Did you happen to remove a section of say 1/4" tubing along the frame and replace it with a larger hose ? That is probably why your pressure went up.

csutton7

in which of the above sceanarios is the LP working harder??? the closer one to the supply or the one further away?? the one further away because---

I'll say it again--electric fuel pumps are pushers not suckers---pressure only means so much--volume is more what is needed--but since we don't have volume guages we use a pressure guage and we are stuck with this pressure phenom as being what's important and it is, as it shows us what is happening with our DODGE LIFT PUMP's health---so we like to see a positive pressure of 12-14psi at all times as that's what DODGE says and it's what the VP wants---do we get this with the stock system--NO I'd say, but there's some trucks out there that seem to defy this, but far to many that don't---thus the LIFT PUMP dilemna---so pressure just tells how our lift pump is reacting to the situation at that moment and over time--

back in 2001 I punched a hole in the bottom of my tank and have changed the Aeromotive pump once(3.5yrs) and it didn't need it after all---I had a loose wire and didn't catch it until I had the new Aeromotive in---so now this recent pump has been in 1.5 yrs and runs as strong as the day I installed it--100% gravity fed and the power is supplied thru a relay that's triggered from the OEM pump wire---these two things are crucial IMO to a pump that can have a chance to live a long life---

so if you can't gravity feed your pump 100% the next best thing is to get it as close to the tank as possible to cut its sucking distance and power it thru a relay-----chris

Superduty

THEY ARE ALL WORKING THE SAME. The motor will flail away until it gets fast enough that it runs out of power to go faster and the result will be 12 PSI.

It doesn't matter if the pump has 12 PSI of vacuum on its inlet and no pressure on the outlet or 12 PSI of pressure on the outlet and no vacuum on the inlet. THE PUMP IS DOING THE SAME JOB.

If the hoses are the same in the circuit with the same resistance than the same pump operating at the same pressure will give the same flow whether it is pushing or pulling. 12 PSI of pump placed *anywhere* in the circuit, pushing or pulling will do the same flow. It doesn't matter which end of the hose you put the pump on.

The only caveat is that the inlet pressure on the pump can't be so low that it cavitates.

One more thing: it didn't matter one iota that your pump drew from the bottom of the tank or the top. Not one bit. It is the same difference as moving the pump up or down. The only difference is that drawing from the top, the pump has to start the siphon. But once the siphon starts, no difference. (Assuming the same size and length of lines in both cases.) The net head is the same in both cases.

bentwings

haha, Who gives a rat's as long as the system works better than the OEM. The real problem is that us Cummins guys have too much time on our hands because the trucks don't break like the F's and C's do. they spend more time really fixing things while we try to fix things that ain't broke just for something to do..

Put the LP on the frame, run the lines, plug in the wires and forget it. It works and that's that. That's where it should have been in the first place.

As for the flow stuff, I'm a ME by trade so I've been through the fluid stuff, the heat stuff and the chip stuff. Why do stacking 2 turbos make more boost than either one alone??? same deal. Superduty is the preacher. ..believe ...you'll save yourself. haha

as for the airplane vs the runway, I posted the question on the model airplane forum before Christmas. It's still going strong with over 5000 hits and a 1000 replys. Some one even restarted it because the "flames" were getting too hot. anyone wanna restart it????
and just for those that don't believe the plane will fly...yes it will very nicely...thank you. haha no more about that.

Superduty

Turbos and fuel pumps are not the same. Ever heard of compressible and incompressible flow ? haha

A turbocharger is a centrifugal pump pumping air (a compressible fluid) driven by a turbine. A fuel pump is a positive displacement pump pumping fuel ( a non compressible fluid) driven by an electric motor. There is no comparison whatsoever.

csutton7

superduty--you don't seem to understand what is known by all electric pump manufacturers---call them and ask them if they like the pumps to be gravity fed or if it's ok to have them suck fuel--they all say gravity fed--thus in your scenario the pump furthest away has to work harder to keep its prime--thus burns up faster--especially on start up--chris

Superduty

Then why does the CP3 feed pump on the Duramax suck fuel all the way from the tank to the CP3. And before you tell me it is different, it isn't.

And if this is known by all pump manufacturers then it must be documented somewhere. Please show me said documentation.

Here is the Holley pump page.
http://www.holley.com/types.asp?type=76

This page lists maximum pressure, it gives flow curves, it mentions the fuel the pump does and does not work with.

NOT ONCE, ANYWHERE does it say anything about mounting the pump close to the fuel tank, or what the maximum inlet vacuum is on these pumps. What does that tell you ? It tells you the inlet pressure and thus the pump mounting location doesn't matter.

If the pump output depended on the inlet pressure, then there would be a footnote to the pump curves or there would be multiple curves for various inlet pressures. THERE IS ONLY ONE CURVE FOR EACH PUMP.

csutton7

http://www.holley.com/data/Products/...ech%20Info.pdf


check out the schematics on the last page--all show the pump below the tank and all show the feeding fuel lines are connected on the side at the bottom of the tank or on the bottom of the tank--chris

Superduty

Those are schematics, not actual placement diagrams. Do you think the regulators need to be under the carburetors ? I knew that someone was going to bring that diagram up.

So where are the different flow curves for various inlet pressures ? Where are the notes saying how far to mount them under the fuel tanks ? According to that diagram they need to scraping on the ground !

And if they need to be under the the fuel tank, have you ever seen them mounted there ? To do that on a pickup truck you would have to mount them UNDER the frame rails. And if that was really the case, wouldn't the truck manufacturers mount the tank up higher ?

csutton7

look at mounting procedure--step 1--pretty definitive:

Mount the pump as close as possible to the fuel tank(at or below the level of the fuel tank pick up.......NOTE:increasing distance between pump and tank will decrease pump efficiency.

http://go.mrgasket.com/pdf/110_140.pdf

csutton7

it's on the first page of both I suggest you read it thoroughly

http://www.aeromotiveinc.com/usrbin/...umps/11101.pdf

http://www.aeromotiveinc.com/usrbin/...umps/11203.pdf

---found the Holley pump mounting instructions--read it and weep right there where it says--Pump Mounting and Installation

http://www.holley.com/data/Products/Technical/199R10367.pdf#search='electric%20fuel%20pump%20ins tallation%20instructions'


chris

Superduty

That is a racing pump ! Those recommendations exist because the pump will starve when all the fuel goes to the back of the tank on takeoff.

================================================== ==
If you are using a stock fuel tank, install a reservoir style sump in the bottom-rear of your fuel tank. Exercise extreme caution and follow all manufacturer's recommendations when installing a reservoir style sump.
If you choose not to install a reservoir style sump, then you must install a high flow capacity fuel tank pickup.(Installing a high flow pickup instead of a reservoir style sump may shorten the fuel pump life and cause driveability problems. When using a pickup, you should maintain at least ½ tank of fuel in the vehicle at all times, to avoid possible engine &/or fuel pump damage.)
For long term driving applications where continuous run times exceed 30 minutes and fuel capacity is less then 10 gallons, Aeromotive recommends the installation of a pump voltage control module, Aeromotive p/n 16302
==================================================

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Note: It is recommended that a fuel shut off valve be installed between the fuel tank outlet and the fuel pump / filter assembly inlet, these valves are available from most popular racing fitting manufactures; Aeroquip, Earl's, Goodridge, Russell, etc.
==================================================


The next time I build a drag racer I will be sure to mount my fuel pump under the fuel tank and put a sump under the back of the tank. Because you never know when your diesel truck will need to pull 5Gs on launch. And I'll also be sure to shut it off before I drive it for 30 minutes. And I'll never drive with less than a half tank of fuel.

I guess I better preface my remarks saying that I am not designing the fuel system for drag racing purposes.

Of course fuel runs downhill and mounting a pump under the tank will make sure it has fuel via gravity. That doesn't mean that for normal applications there is anything wrong with having the pump suck fuel from the tank.

On the 99+ Superduty the fuel pump is mounted 6 feet from the tank pickup (crew cab) and there is nothing stopping the manufacturer from mounting it closer. And the fuel pump is mounted near the top of the pump. It would have been easy to mount it lower.

And there are still no curves derating the pump for the distance it is mounted above or below the tank.

Have you looked at the fuel system on over the road trucks ? Where is the lift pump ? Is it mounted below the fuel tanks ? Is it mounted close to the tank ?

Superduty

==================================================
The best location for mounting any electric fuel pump is the rear of the vehicle, near the fuel tank and in a position that will allow the fuel to be
gravity fed to the pump. The pump should be mounted on a solid member, such as the chassis, in a vertical position with the pump motor on...
==================================================

Sure. It primes easier. Notice it doesn't say it MUST be mounted there. And it doesn't derate the pump if it isn't mounted there. And it doesn't say it pumps more if it is mounted there. And it doesn't give curves for different mounting positions. It also doesn't say you can't mount it above the fuel tank nor does it give a maximum distance the pump is to be mounted from the tank.

Notice it also says the pump has to be mounted upright ! Apparently gravity affects fuel flow in a fuel pump.

Do you know what a DD 71 and 92 series engine is ? Guess where the fuel pump is ? How high is the pump in the engine above the fuel tanks on a highway truck ? They seem to run OK.

This is friggin hopeless. The original question was does the output of the fuel pump increase if it is mounted closer to the tank. The answer is no. Provided the input isn't cavitating and the vehicle isn't pulling 5G with all the fuel sloshed to the back of the tank.

What a total waste of time it is to try to teach people something.