Another fuel tank plumbing option

[nkemp]

Just a note that the sequence of operations applies better to the sump that has the fuel pickup inside the sump. The other design (and there may be more I am unaware of) pumps from the bottom of the tank (outside the sump) and is backed up by the sump.

Nick

[Bitsyncmaster]

Just a note that the sequence of operations applies better to the sump that has the fuel pickup inside the sump. The other design (and there may be more I am unaware of) pumps from the bottom of the tank (outside the sump) and is backed up by the sump.

Nick

This is kind of fun thinking about this so I'm not trying to prove anything but just explain it. I'm still very open minded and just looking for an answer. The sure way would be to do an experiment with the hardware but that is to much work.

I assume the pump pickup in the sump is as low as it can be. I also assume the pick for the tank is as low as it can be. So I don't understand the advantage of a dual pickup inside and outside the sump.

[nkemp]

This is kind of fun thinking about this...

I agree.

So I don't understand the advantage of a dual pickup inside and outside the sump.

I agree again. It is not clear how/why some sumps are built the way they are. But I'm going out on a limb here and say that GM and its engineers had a good reason.

I wish you could see the sump I have that has the pump connected to a pickup outside the sump. That one is relatively simple to understand. The other, that has the pickup in the sump and the thin line off the top of the pump and a float valve does not make sense to me. And although I'm fond of saying that Google knows everything, it has not offered up its secrets on the sump operation.

Instead of using gas to test pumps, I've read that some use water. The advantages are obvious.

Nick

[Ron]

Maybe it is worth the thought process to create an equation...Infinite input to sump (in finite terms) -pumped out + returned = sump level. How's that for a crude equation:-)

I don't think it's crude...let's see if I can play mathemagician (with a rusty pencil ;-)

SumpLevel = FuelIn - FuelOut
FuelIn = CkValveFuelIn + Return
FuelOut = PumpOut
Return = PumpOut - Used
By substitution;
SumpLevel = (CkValveFuelIn + Return) - PumpOut; [~your equation]
SumpLevel = (CkValveFuelIn + (PumpOut - Used)) - PumpOut
SumpLevel = CkValveFuelIn - Used *

SumpFillRate > 0 IF TankLevel > SumpLevel AND CkValveFuelIn >= Used
IF SumpLevel > TankLevel Then SumpFillRate <= 0

Suppose you start with a full sump and a half tank. If you turn the key on, the fuel in the pump will simply circulate because the check valve will not let any in the sump (after purge and pressure up...) If you then start the engine, it will lower the sump level at the rate the fuel is being used, until the levels match (check valve about to open). From here on is where I differ with either ideal, so far.
I believe saying that the pump draws fuel out of the sump and the check valve will instantly let more in make sense except the fuel being returned (already) is not accounted for (no time to rush in before return)...or maybe better said - the return is Constant and will replace what fuel the pump removes minus the fuel used, so the check valves will only allow the net loss, matching the tank level, which is reflected in * above.

Me thinks

[DMCVegas]

I don't think it's crude...let's see if I can play mathemagician (with a rusty pencil ;-)

SumpLevel = FuelIn - FuelOut
FuelIn = CkValveFuelIn + Return
FuelOut = PumpOut
Return = PumpOut - Used
By substitution;
SumpLevel = (CkValveFuelIn + Return) - PumpOut; [~your equation]
SumpLevel = (CkValveFuelIn + (PumpOut - Used)) - PumpOut
SumpLevel = CkValveFuelIn - Used *

SumpFillRate > 0 IF TankLevel > SumpLevel AND CkValveFuelIn >= Used
IF SumpLevel > TankLevel Then SumpFillRate <= 0

Suppose you start with a full sump and a half tank. If you turn the key on, the fuel in the pump will simply circulate because the check valve will not let any in the sump (after purge and pressure up...) If you then start the engine, it will lower the sump level at the rate the fuel is being used, until the levels match (check valve about to open). From here on is where I differ with either ideal, so far.
I believe saying that the pump draws fuel out of the sump and the check valve will instantly let more in make sense except the fuel being returned (already) is not accounted for (no time to rush in before return)...or maybe better said - the return is Constant and will replace what fuel the pump removes minus the fuel used, so the check valves will only allow the net loss, matching the tank level, which is reflected in * above.

Me thinks

An easier way to put it would be like this:

The sump is baffled. It's even called a Baffle in the Parts Catalog. Take a look at it:



Now what you've got to picture here are those small holes in the bottom. They of course allow fuel to flow INTO the Sump.

Picture the car at a static position and not moving at all. Fuel Pump is running, and it's draining liquid out of the Sump. As the Fluid level lowers, Liquid on the other side flows in through the Baffle on the bottom to take it's place until the levels are equalized on both sides. Simple physics.

Now throw in the Fuel Return line that is forcing fluid into the Sump. Certainly it will slow the flow of liquid flowing into the Sump through the Baffle because it's an additional source being forced in mechanically, but the Flow Rate into the sump below from the Baffle will always be there to make up the difference and adjusts accordingly to ensure this.

But what about times when the fuel level is extremely low, and the car is subjected to an extreme angle where the baffle can't refill itself as quickly, or in an extreme situation, at all? To figure that out, the math involved here would work like this:

First off as far as the pump is concerned we know that the outbound flow rate is higher than the return. So we know we've got a Deficit on our hands. However we still would need to measure the flow rate in terms of CC's per second. We would need to know this because while we certainly have a deficit, what we still haven't figured out is exactly how long it takes to drain that whole Sump. Once we know that, we would then in turn know exactly how large the Sump would need to be in order to sustain the vehicle through tight curves.

What this exact value is I've no idea. However my guess is that the existing baffle/sump that we use is already the perfect size. Even with my Low Fuel Light on and the Stock Setup running, I myself have never had my car sputter. But still we have to consider the Baffle below and it's filling of the Sump. In certain cases it might not fill if the fuel is sloshed too far away (and potentially even create an additional drain), but I seriously doubt that any of us would run into such a situation at all? Why?

There are still a couple of things to consider here:

First is how much fuel exactly is left inside of the Tank when the Low Fuel Warning Light comes on? I believe that according to the manual you should have enough fuel to still make it about 30 miles. Figure on having about 1½ to 1¾ gallons of fuel left in the tank. With that VERY flat fuel Pick Up Screen, I imagine that even at that low fuel amount in the tank that it would still remain submerged and would allow the car to run long enough to get to a gas station. No matter how big of a sump you've got, it's not going to work if you don't have fuel.

Second off, it's a passenger car, not a rock crawler. Short of doing donuts or drifting the car at higher speeds with the tank almost empty, I seriously doubt that the car will ever be subjected to the sorts of velocities needed to slosh gasoline over to one side of the tank to run the Fuel Pump pickup run dry, nor would we be encountering parking garages with such extreme ramp angles to cause this either. If we ever did, I doubt our cars even have the approach angle to get to these ramps.

[Bitsyncmaster]

I guess you don't drive in the mountains. In western Maryland you hit many 7 degree grades up to 5 miles long. That is where the stock baffle will work better than the straigt down baffle. But no matter how you design it, you just don't want to let the tank get low driving in the mountains.

I've never had problems with the stock setup but I know to not let the tank get to low. Even with instalation of the a new pump, it's not that big of a deal since it's done so seldom.

[DMCVegas]

At this point, it appears that using the existing pump (they are cost effective and perform well) coupled with the GM sump and plumbing the lines through the tank provides a superior fuel pump solution while providing a cost effective solution.

That's the thing though. I'm not proposing a replacement pump/sump assembly. What I'm proposing is a Cartridge that we would load the DeLorean Fuel Pump and Return Line INTO. It could either connect up to the stock Baffle and Fuel Lines, or we could just mold the Sump & Check-Valve into the bottom of this cartridge. This way we don't have to search for an existing pump, let alone try to modify it to adapt it to our application. We're just recycling proven parts here.

I've pondered adding threads some how and a piece attached to the tank may work. My concern is that one with sufficient thread and backing material would no longer fit the threaded locking ring. Another option is to insert "nubs" into the tank plastic in a thread formation that the locking ring could thread onto. But anytime you put a hole in the tank you need to think about how to seal it. So one solution causes another problem and you keep pushing the problem down the sequence.

Nope. Instead of looking for replacement parts, we could just mold our own. A molded ring that goes around the flanged opening of the Fuel Tank and is welded or epoxied to the tank, and a ring that's meant to go with it. If nothing else, I know that this stuff right here will work perfectly:




Having parts to put my car together when I was in a pinch once, I had to use a Volvo Pickup screen. Of course there is no way to attach it properly to the DeLorean, so I actually used this putty to attach it. Plus when I had my TankZilla start to leak because of too much positive pressure, I sealed the top with it. I can attest that this stuff after 2 years in my gas tank was solid as a rock and remained attached to both the filter as well as the pickup hose. Plus the stuff on top of the TankZilla has permanently attached itself and isn't going anywhere either. I'm hoping a chisel will take it off, but we'll see. In any case I do believe that there are some solutions here that will work for us. After all we're just trying to use enough pressure to firmly seal the Fuel Pump Gasket this assembly would use. It's not like we need gobs of torque here, and would most likely never see enough to break the attached threaded ring loose. Liquid would be more ideal than putty however, and a thick bead along the crevices of that flange would work perfectly.

This way we only need to mold 3 new parts, and nothing as expensive as a new gas tank. That way costs are kept down in terms of both parts and labor for such a retrofit.

Whatever a solution might be, I still think that eliminating that Fuel Pump Boot will probably eliminate lots of garbage in the gas tank in the future since we're seeing more and more fuel with ethanol in it.

I used to live in Nevada which is the most mountainous state in the Union. Plus it's full of casinos with some STEEP ramps (anyone here got to DCS Vegas and remember Palace Station's Garage?) Flat land there doesn't last that long, and those kinds of grades there were very common place as well when you were trying to drive down to some of the beaches on the Colorado river. But even with those steep grades I've never had a problem either, and I believe that's probably due to the stock Baffle and Tank's properties. I honestly don't believe that this will be as much a concern as people are worried about.

[Ron]

An easier way to put it would be like this:
...
Picture the car at a static position and not moving at all. Fuel Pump is running, and it's draining liquid out of the Sump. As the Fluid level lowers, Liquid on the other side flows in through the Baffle on the bottom to take it's place until the levels are equalized on both sides. Simple physics.
....

I thought that was the general thought earlier...

I'm with you on the rest, but the later discussion was about a sump/baffle* with check valves (not free flowing holes) and a return into the baffle/sump
RE: this design (from his earlier post although the valve is not shown )
http://dmctalk.org/attachment.php?at...6&d=1318953278


*...it bugged me ?too? that "sump" and "baffle" was being used interchangeablyin the thread sometimes...Seemed sump was the term settled on to me LOL (maybe an error on my part there)

[Ron]

Having reread it all, I officially choose to say, "Dave is right".

[nkemp]

The nuances of sump Vs baffle are subtle. I looked up the definitions and they are summarized as follows:
Sump: A pit or hollow in which liquid collects
Baffle: A device used to restrain the flow of a fluid

I'll take credit/blame for trying to differentiate designs as "sumps" or "Baffles". I was proposing that the D works better when the pickup is in a sump (collected fluids) vs baffled (fuel is restrained from moving around). A round aluminum tube surrounding the pickup acts more as a baffle to restrict fluid flow. The GM units (used simply as an example) collect fluid, presumably with levels differing inside and out and as such matched the definition of "sump". It was proposed to me a couple years ago that the original D design is as a sump.

All said and done, let's not get too hung up in the terms as long as we are clear about the function. Are we trying to keep the fuel from moving around or are we trying to collect some fuel in a "container" from which we can extract fuel? I propose the latter works better... kinda like a tank in a tank.

So does that clarify or mudify the sump vs baffle discussion?

Nick