Help me understand how an in-line fuel pump pumps more fuel...

[excell]

How does an in-line fuel pump pump more fuel through the in-tank that is lacking? You figure it would do nothing since the in-tank cannot pump anymore than it already is. Right?

 

Help.

[Berto]

i may be totally wrong on this

 

 

but if its like the turbine systems we are studying now then this should be right

 

the compressors(pumps) should have a pressure ratio pressure at outlet = pressure ratio * pressure at inlet (under ideal circumstances)

 

 

so if you have the incresed pressure from the first pump, u'll have increased pressure after the inline.

 

 

i think i misunderstood your question.

[excell]

Ok, let me try and clarify.

 

If my in-tank pump was unable to keep up with fuel demand one solution would be to install an in-line. But how does the in-line solve this? How can it allow the in-tank to flow more fuel than it could without the in-line?

[smokinHawk1647545499]

think it helps pressure wise, and pushes the fuel some so the intake doesnt have to strain so much

 

least thats how i thought it works, could be wrong

 

but ys an inline doesnt help that much more, you really need a bigger intank or two like i have.

[excell]

It's bad when you are out of fuel with a 255lph in-tank and a V6.

[desperado]

Fluid Dynamics 101

 

Two reasons. As far as flow, first thing is that you loose flow by presurizing the outlet of any pump. If you have two pumps in a line the first pump does less work and therefore can pump more volume because it has less pressure on the output side due to the second pump in the line. The second pump does not have to work as hard to created to same amount of flow because the inlet is pressurized and not at a vacuum like the first pump is, or any stand alone pump will be.

 

The other reason, and it seems more to what you are asking is that most pumps do not restrict flowthrough, by this I mean that even with the pump turned off, if fuel is sucked through it, it will allow fuel to flow. Most tank pumps are turbine pumps, sort of like a turbocharger, of course a turbo will flow air through it even if it's not to speed.

 

Now the other the thing that happens it the two pumps share the load. Neither of the pumps does as much work as either would do alone.

 

The tank pump does not have to work against the same pressure on the engine because there is a second pump sucking fuel into it and pumping it on to the motor, the second pump does less work because the inlet is pressurized and it does not have to build as much pressure to ge to the required prussure. This also applies to flow.

 

Now if you are wanting to do this right, there are some sizing considerations but just sticking a pump in line is going to help. I don't know what you are feeding or what your plans are, if you need some more info let me know.

 

Hope this helped.

[desperado]

I just read your reply, and saw your fuel flow requirements.

Just sticking an inline pump in will help for a while, but it's a bandaid at best.

 

V-6 needing over 255lph, my guess is it's a turbo and you are spraying it to boot. Just guessing at this point but that is alot of fuel.

 

Your lines, if factory are going to become a restriction here real quick, if they are not already. So you might want to start considering a major rework of the fuel system.

 

If you are spraying, you can run a seperate fuel system and pump for the spray, and that will take some of the load away from the primary system, The other thing this enables you to do is run better fuel with the spray, but I don't know for sure that you are spraying, but that is just alot of fuel requirement to not be.

[Buck531]

He's not spraying, he just has an enormous blower on top of the engine.

[zeitgeist57]

+1 on factory lines not flowing enough. Braided stainless steel lines? -8 AN fittings?

[SupraGlue]

For a more affordable fuel line than braided stainless, take a look at the Aeroquip AQP lines. They use a fabric coating and a press-over-barb system of securing the lines to the fittings (AN sizings). One thing this eliminates is abrasion from the stainless braid, if you have an area where the lines will rub against something.

[Doug1647545489]

When I had my inline it was more to take some strain of the intank pump and help keep my pressure up. Didn't actually flow anymore amount of fuel.

[slow4now]

As already stated an inline pump doesn't increase the volume of fuel that is pumped, but it increases fuel pressure thus injecting more fuel per injector pulsewidth.

On a heavily modded car an inline pump is not the way to go. Excessive pressure could cause injector failure or fuel line rupture, not to mention less than optimal fuel atomization.

[desperado]

Doug said : When I had my inline it was more to take some strain of the intank pump and help keep my pressure up. Didn't actually flow anymore amount of fuel.

 

As did the man with no name made a similar statement.

 

 

Sorry, but ERRRRRRRRR. you missed the ten million dollar question. If you are pumping a fuild, and it is a balanced system, and you increase the amount of flow at the outlet until the pressure falls, you MUST INCREASE FLOW in order to reestablish the original pressure. There is no way around this. So if putting a second pump in line does increase your pressure, it does so by increasing flow.

 

And in a return flow regulated system, there is constant flow, the pump is never dead headed (pumping against a closed system) the regulator does its job by passing enough fuild back to the reserve (gas tank in this case) to maintain the pressure in the system.

 

Laymans terms, if you build your shit to take so much fuel that the pump can't maintain pressure you have to put a pump in that will FLOW more fuel in order to restore the pressure you had.

 

Did a full year of fuild power and fuild dynamics in college. Focused on mostly hydraulic systems, but it is all one in the same when it comes to basics.

 

Now the ONLY WAY to increase pressure of a return flow system, is to either readjust the regulator, or to put more flow in the system than the regulator system can bypass. If this is done in a fuel system it will just burn up the pump/s. And pressure will be very high until pumps fail.

 

If you do it with a hydraulic system, it will burst the weakest link in the system, but a hydraulic pump is designed for 5000 psi at a specific volume. Been there, done that and got soaked with 20 gal of hydro fuild.

 

[ 17. February 2004, 04:57 PM: Message edited by: Desperado ]

[Doug1647545489]

Originally posted by Desperado:

Doug said : When I had my inline it was more to take some strain of the intank pump and help keep my pressure up. Didn't actually flow anymore amount of fuel.

 

 

Now the ONLY WAY to increase pressure of a return flow system, is to either readjust the regulator, or to put more flow in the system than the regulator system can bypass. If this is done in a fuel system it will just burn up the pump/s. And pressure will be very high until pumps fail.

 

I never said i was using the pump to increase pressure.

[rl]

http://www.modulardepot.com/?show=articlesdet&aid=24

 

Read smile.gif The guy who wrote it knows what he is talking about.

 

 

Desperado basically said everything I would have said, he is 100% correct.

[desperado]

Originally posted by Doug:

I never said i was using the pump to increase pressure.

Well you did and you didn't. By adding the second pump you were maintaining pressure, but in reality, you were increasing it, from where it was low back to the standard level. And to do that, you increased the flow. You were doing it to maintain pressure, because your fuel flow requirements were greater than the single fuel pump could flow and maintain the pressure.

 

Look at it like this. A power washer pumps water at a very high pressure, anywhere from 2000 to 3800 PSI, through a small orifice. That is fixed. It you take off the orifice (nozzle) the pressure drops drastically. The reason is pump is designed to build a certain pressure at a given flow. By removing the nozzle you increase flow capacity. Same thing happens when you increase pulse width on an injector, it is open longer, and flows more. Now if it flows more than *** pump that supplies it can pump through and maintain the rail pressure, it will drop.

 

The only way to get the pressure back up is to increase flow. Because the flow requirements have changed. Pressure is a restriction of flow. I wish I could explain this better, but that is as good as it gets with the online explanation. Catch me at Geeros and I will go deeper for those that want to know.

[excell]

Well it looks as if I have some figuring out to do with the fuel system.

 

Here are a few details:

 

First and second gear are fine, in third gear I am running out of fuel. I believe this to be a combination of lower voltage to the pump as it gets hot(resistance) and also pressure loss as it's been running at full for about 7 seconds before I actually hit third.

 

I'm trying to solve this issue so that if I want to go mess around, say oh in a roll situation on the fwy, that I don't blow the motor up because it runs out of fuel.

 

Trying to figure out my options as the Walbro 340M is the biggest pump I can fit in the tank.

[slow4now]

Originally posted by Desperado:

Doug said : When I had my inline it was more to take some strain of the intank pump and help keep my pressure up. Didn't actually flow anymore amount of fuel.

 

As did the man with no name made a similar statement.

 

 

Sorry, but ERRRRRRRRR. you missed the ten million dollar question.

Negative ghost rider.

 

 

You are wrong. smile.gif

A intank fuel pump does not increase flow, it increases the pressure in a fuel system between the inline pump and the injector.

 

If you setup two walboro 255lph fuel pumps so that they would both pump fuel into a bucket, but one of them had an inline fuel pump between it and the bucket you would find that they both flow the SAME AMOUNT OF FUEL in a given time. That is RATE OF FLOW.

If you could measure the force with which the fuel was entering the bucket, the setup with the inline pump would be spitting the fuel out with more force (Pressure = a measure of force).

 

Now, add injectors into the equation. You are increasing the flow rate at the INJECTOR with the inline pump because there is more pressure ( aka force) in the fuel system forcing (there's that word again) more fuel through the injector per pulsewidth than that of the intank only system. Note however that the inline pump is not increasing the flow capacity to the injector! Hence the limitations of the inline pump band-aid!

 

 

Now the ONLY WAY to increase pressure of a return flow system, is to either readjust the regulator, or to put more flow in the system than the regulator system can bypass.

Ways to increase pressure in a return fuel system are to restrict the return flow, or use an inline pump or higher pressure intank pump.

 

In your first paragraph you said:

" If you are pumping a fluid, and it is a balanced system, and you increase the amount of flow at the outlet until the pressure falls, you MUST INCREASE FLOW in order to reestablish the original pressure. "

 

Using a fuel injection system as an example, since thats what we're concerned with here..an inline pump is a band-aid to overcome injectors that are too small. When you upgrade the fuel system you are doing so because the engine demands more fuel to safely make more power. Once the injectors are upgraded they can/will flow more fuel than the intank/inline combo can provide to them thus the need to replace the intank pump with one (or multiple) that has an increased flow capacity.

[slow4now]

Originally posted by Osirian:

Well it looks as if I have some figuring out to do with the fuel system.

 

Here are a few details:

 

First and second gear are fine, in third gear I am running out of fuel. I believe this to be a combination of lower voltage to the pump as it gets hot(resistance) and also pressure loss as it's been running at full for about 7 seconds before I actually hit third.

 

I'm trying to solve this issue so that if I want to go mess around, say oh in a roll situation on the fwy, that I don't blow the motor up because it runs out of fuel.

 

Trying to figure out my options as the Walbro 340M is the biggest pump I can fit in the tank.

The only way to be sure if there is a decrease in fuel pressure is to hook up a fuel pressure gauge. Until you do that you are just guessing as to what the problem is.

[rl]

Ways to increase pressure in a return fuel system are to restrict the return flow, or use an inline pump or higher pressure intank pump.

 

In your first paragraph you said:

" If you are pumping a fluid, and it is a balanced system, and you increase the amount of flow at the outlet until the pressure falls, you MUST INCREASE FLOW in order to reestablish the original pressure. "

 

Using a fuel injection system as an example, since thats what we're concerned with here..an inline pump is a band-aid to overcome injectors that are too small. When you upgrade the fuel system you are doing so because the engine demands more fuel to safely make more power. Once the injectors are upgraded they can/will flow more fuel than the intank/inline combo can provide to them thus the need to replace the intank pump with one (or multiple) that has an increased flow capacity.

Flowing into a bucket is not a good measure of anything, it needs to be a pressurized system to work correctly.

 

An in-line pump is NOT a band aid for injectors that are to small, that's called an FMU, an in-line fuel pump is used to support more power and flow MORE fuel at MORE pressure (if needed, like in boosted applications). In a return system that has an adequate FPR and fuel lines the fuel pressure should not raise with an in-line pump.

 

The only way adding an in-line pump will increase pressure in a return system is if it outflows the capacity of the return or the FPR, otherwise it allows you to move more volume at greater pressure (with a FMU or AFPR), but it also allows you to move more volume period.

 

 

Your dealing with a pressure drop across the pump, so say you have a single pump, atmospheric on one side and 42psi on the other, you now have a 42psi pressure drop across the pump.

 

The problem for someone like Chris is that he is running probably 42psi base pressure, but to keep the pressure drop at 42psi across the injector under boost the FPR raises the pressure on a 1:1 ratio with boost, so if he is running 20psi, he is now running 62psi (yet the injectors flow just as much as they would under 42psi, the FPR compensates for the pressure at the tip of the injector). What happens when you have a 62psi pressure drop across a single 255lph pump rated at 40psi? You lose a significant amount of flow.

 

Now- 40psi/(42psi+20psi boost) = .65 sqrt.65 = .806 806*255 = 205.53

 

So you how now effectively turned your 255lph pump into a 205lph pump.

 

Now lets say that you have a 255lph in-tank pump and add a second 255lph in-line pump. The only real way to measure this is to take the pressure between the pumps, but since this is hypothetical, we'll say that there is 20psi between the pumps.

 

Now- 40/22+20 (using 20 because the pressure drop across the pumps is now 20 instead of 42) = .95 sqrt .95 = .974 .974*255 = 248.37 for each of the pumps.

 

You now have over 400lph of fuel FLOW at the given pressure, as opposed to the 205lph of FLOW that you had before with a single pump.

 

Of course the calculations all change with a 255lph high pressure pump (they are rated at 60psi I think), but the ideas are exactly the same.

 

Its basically repeating what is said in that link, read the link if what I said doesn't make sense to you.

 

 

Chris, are you losing fuel pressure in 3rd gear? If so an in-line pump is what will fix the problem correctly.

 

Rob:)

 

[ 18. February 2004, 09:27 AM: Message edited by: rl ]

[desperado]

RL... the voice of reason... thanks.

 

As far as the comment I made about increasing the fuel pressure in a return line regulated system.

 

That was a rebuttal to a comment made by someone that said that running an inline pump would run the pressure to high. And what I was getting at was that the only way that the fuel pressure whould get too high is that flow rate would have to increase to the point that the regulator could not flow enough fuel back in the return to keep the pressure in check. But I don't think that is going to be the case with just adding an inline pump.

 

I also saw that someone said that increasing the restriction of flow would increase pressure. But that is of course counter productive in a fuel system.

To make a specific amount of horsepower, you need to convert X number pounds of fuel per hour into heat energy, which the engine converts into mechanical energy. If you restrict the flow of fuel the power has to drop. But I think that everyone understands this. The whole idea of what we are doing is increasing power, which requires more fuel.

 

Not sure how we got from where this started to here, but it's been a fun trip.

[desperado]

Originally posted by the Man With No Name:

Using a fuel injection system as an example, since thats what we're concerned with here..an inline pump is a band-aid to overcome injectors that are too small. When you upgrade the fuel system you are doing so because the engine demands more fuel to safely make more power. Once the injectors are upgraded they can/will flow more fuel than the intank/inline combo can provide to them thus the need to replace the intank pump with one (or multiple) that has an increased flow capacity.

As far as the injectors being too small, I assumed that if he's running out of flow with a 255 pump the injectors are not stock to begin with. I didn' say that though, but I did figure that was the case. That being said, as far as the flow issue, that is what I was saying all along. If you are requiring more flow than the pump can provide, pressure will drop. Adding anything that brings the pressure back up to acceptable levels without changing the current restriction has to increase flow. So putting an inline pump in, if the pressure comes back up, the flow has increased.

[excell]

I'm running 50# injectors and may be upgrading to 57# in the near future. I run stock 45psi fuel pressure. Yes, we belive the car is running out of fuel pressure.

[rl]

Originally posted by Osirian:

I'm running 50# injectors and may be upgrading to 57# in the near future. I run stock 45psi fuel pressure. Yes, we belive the car is running out of fuel pressure.

What walbro pump are you running? How much boost?

 

Do you have any idea what the BSFC for your engine is? I would assume it's in the .65 range..? We can easily figure out if you need more pump...

 

Regardless, if you are running out of fuel pressure a walbro in-line will fix the problem, it wont raise the pressure either, just allow it to maintain the pressure it requires when you are under boost with that amount of flow. The reason it is running out of pressure is because the single pump cannot maintain flow that is required at the pressure you are running (I'm assuming over 60psi of FP while under boost).

[excell]

I run the Wlabro 340M 255lph in-tank pump. Boost right now is in the 17 to 18 psi range and will be approaching - and probably just passing - 20 this year.

 

What is BSFC?