Another fuel tank plumbing option [Archive] - DMCTalk Forum

nkemp

10-13-2011, 06:41 PM

Let me preface that I dislike the design of the DeLorean fuel pump, boot, cover & plumbing. If we don't have gas on the pump we may have water. Every time you service the tank or pump it is a PITA. We are recommended to not fill the tank so that it does not leak. Owners complain about gas fumes. Parts shrink, deteriorate with gas exposure or tear easily when gas soaked. There are lots of opportunity for leaks and problems. Other than that it is a pretty good design. Yes I've heard that some installations work well... but plenty don't. So much for the rant...

Here is the idea (works with any current pump or sump implementation):

A through the wall, double barbed fitting for the return line installed on the tank top

Inside run the return line from the fitting to the sump of your choice
Outside connect to the return fuel line

Hang the pump in the existing bracket inside the tank

Cut off 1-2" of the exiting boot to pad pump to reduce vibration
Keep pump low in the tank for additional immersion in the fuel to promote cooling and long pump life
Run the hose from the pump inlet to the pickup screen per the sump implementation.

A through the wall double barbed fitting for the pressurized line installed on the top of the tank

Inside run a fuel line from the fitting to the pump outlet
Outside connect to the pressurized line.

Use through the wall electrical connections for the pump on the top of the tank.

This could be run under the boot (yet to be discussed) but could be a point of leakage
Could be installed through the boot but why not install on the tank top?
There may be other options...

Use a cover (flat top or slightly domed) that covers completely the fuel pump hole. Not like the current boot with mounting hole for pump and return line but one that is a cover, no holes and is secured with a hose clamp

This is where I came to an end ... I can't find a cover for the hole. Anyone have any ideas? I don't think a plug would work

OD of tank opening at fuel pump opening = about 111mm/4.37"

A fiberglass one could be molded pretty easy but likely requires some form of rubber gasket or O-ring
The pump is now totally in the tank per today's fuel pump installations

If the pump leaks a bit it is in the tank

There is no "pond" to collect any water and no fighting with the pump cover

In this design, servicing the tank/pump is a lot easier since the lines use through tank fittings and are not disturbed. The return line should never have to be serviced. The supply line can be removed from the pump if the pump is removed. Water cannot collect on the pump. Gas leaks are not a concern.

As indicated above I have been unable to find a boot to cap off the pump opening. I know that one could be molded using the existing boot material. I was hoping to find an off the shelf solution for capping off the tank.

Any thoughts, ideas or sources?

Nick

Farrar

10-13-2011, 06:50 PM

How about a plastic peanut butter or mayonnaise jar lid to cover the hole? That'd probably be big enough.

Farrar

nkemp

10-13-2011, 06:52 PM

It needs to be flexible enough to tighten down with a hose clamp. And the threads would likely leak if gas was splashed or filled up to the top.

Farrar

10-13-2011, 07:01 PM

It needs to be flexible enough to tighten down with a hose clamp.

Why?

And the threads would likely leak if gas was splashed or filled up to the top.

That's what big O-rings are for. :)

Farrar

LEVY

10-13-2011, 07:07 PM

Do you really believe he is serious?

It needs to be flexible enough to tighten down with a hose clamp. And the threads would likely leak if gas was splashed or filled up to the top.

Bitsyncmaster

10-13-2011, 07:20 PM

I like your ideas.:wink:

I put the boot clamp on the pump boot so it holds tight, never leaks, can fill the tank right to the cap. Then I just use tywraps to hold the outer cover around the clamp. Have to make a small cut in it to clear the clamp worm gear.

I've also thought about making a sump in the tank so you could run it empty without intermittent stalling. But you would need a sump extending below the cover plate so not to safe.

LEVY

10-13-2011, 07:42 PM

Hope you are not talking about Farrar ideas!

I like your ideas. .:wink:

I put the boot clamp on the pump boot so it holds tight, never leaks, can fill the tank right to the cap. Then I just use tywraps to hold the outer cover around the clamp. Have to make a small cut in it to clear the clamp worm gear.

I've also thought about making a sump in the tank so you could run it empty without intermittent stalling. But you would need a sump extending below the cover plate so not to safe.

nkemp

10-13-2011, 08:42 PM

I like the GM pump assembly/sumps. They use back-flow valves allowing the fuel in the sump to remain higher than the tank fuel level yet fuel can flow in from the tank or over the top depending on tank level. This helps keep the fuel pump cooler as well. It also has a built on fuel level sensor ... with the wrong configuration for the D

check out: http://www.gasgoo.com/auto-products/fuel-system-393/1142527.html

That said, it does not get any lower than the flat bottom tanks we have.

I've heard that the original design would allow pumping the tank nearly dry. If one has a baffle then it is difficult to get all the gas out. If one has a sump arrangement, which the original was supposed to be, the return fuel keeps it full avoiding stalling on turns while pumping a long ways towards dry.

But the design is less than optimal. So I'm thinking the GM sump might be a nice addition.

Farrar

10-13-2011, 11:00 PM

Do you really believe he is serious?

I will be the arbiter of my own seriousness, thanks very much whoever you happen to be.

If there's no need to remove the cover for the hole where the old fuel pump used to be, one could simply RTV a piece of plastic to it. I was under the impression that the original poster was seeking help. I offered some. But my ideas evidently suck since they're not high tech. Or I was mistaken in my assumption that the original poster was seeking help. Either way, AMF.

Farrar

AdmiralSenn

10-14-2011, 12:33 AM

I think redesigning the pump and ports is a great idea. I'd be tempted to do this even though my (OEM style) fuel system is currently working great.

I think you're right in pinpointing the tank seal as the hardest part since it's likely to require a one-in-a-million crossover part or something custom.

nkemp

10-14-2011, 01:11 AM

If there's no need to remove the cover for the hole where the old fuel pump used to be, one could simply RTV a piece of plastic to it.

Farrar

I think one can assume that one would need to get into the tank again. For example the pump may fail (will over long enough usage) and need replacement.

So the issue is finding or making a tank pump hole cover. At this point I'm pondering a fiberglass cover molded to the original top portion of the boot to seal the tank. I'm not sure how well the two would bond or how well they would bond using Polyurethane or similar. It would be attached to the tank with a hose clamp like now and thus could be removed to be serviced. BUT I still hope for a better idea.

Nick

LEVY

10-14-2011, 06:13 AM

.

How about one piece of metal with a gasket for the outside (round) with a hole in the middle. For the inside, a "T" shaped rod with thread on one of the legs. You insert this T inside the tank with the tread facing up, this threaded rod will go thru the hole in the metal cover, then a nut to apply pressure and you have your cover secure.

Of course, this is just a basic idea, this "T" can be made hinged and already attached to the cover to make it easier to use.

This "T" can even have hinged nut in the middle instead of a threaded rod, this way you slide a bolt thru the cover and nothing will stick out from the thank.

Hope someone else can explain this better than me but this is the idea.

I think one can assume that one would need to get into the tank again. For example the pump may fail (will over long enough usage) and need replacement.

So the issue is finding or making a tank pump hole cover. At this point I'm pondering a fiberglass cover molded to the original top portion of the boot to seal the tank. I'm not sure how well the two would bond or how well they would bond using Polyurethane or similar. It would be attached to the tank with a hose clamp like now and thus could be removed to be serviced. BUT I still hope for a better idea.

Nick

sean

10-14-2011, 07:43 AM

If there's no need to remove the cover for the hole where the old fuel pump used to be, one could simply RTV a piece of plastic to it.

I use gasoline to clean up RTV, so im not sure how well its going to seal for ya.

nkemp

10-14-2011, 11:05 AM

How about one piece of metal with a gasket for the outside (round) with a hole in the middle. .

If a a center bolt is used, a gasketing washer would be needed to minimize gas leakage and gas fume leakage around the bolt.

To build on this idea... one could use the top of the existing boot as the gasket. Cut it so that the crosscut profile looks like an upside down "U". Now take the metal and put a lip around it like a jar lid (building from Farrar's post) so that it stays centered over the gasket. This is where a little adhesive would help to hold the two pieces together.

If the adhesive works well then the bolt is not needed (and maybe not the lip as well). Simply hose clamp the gasket to the tank lip like it is today.

Another method, which I'm still lukewarm on, is to bolt through the top part of the upside down "U" gasket through the metal disk to secure the two. This would still need sealant between the gasket and the metal plate. And the screws might pull through the rubber boot material... A metal ring inside the upside down "U" would minimize tear-through.

The more I think about this the more options...

Cut the existing boot so that it looks like an upside down "J" with the longer leg inside the tank. Use angle brackets with one leg against the gasket and the other the top. Use sealant between the metal top and the top of the "J" gasket. To prevent gasket pull-through a flat metal band could encircle the boot where the screws/rivets go through. The top could be spot welded or bolted (use sealant) to the brackets

BTW ... if metal is used for the seal/cover, the pump's electrical ground connection could use the metal (in other words, no electrical isolation from the metal seal. Then only one wire would need to pass through the tank wall. But... when removing the tank cover, the electrical connection may hinder its removal).

NK

Reminder: I'm "subject to being wrong without notice." ;)

LEVY

10-14-2011, 11:51 AM

.

Yes, I forgot to mention that, something like a plastic washer, like in this order: bolt - metal washer - plastic washer (gasket)- fuel tank.

With this setup, no additional sealing material is needed, for easy of service.

Maybe we could use a specially made plug like the one used to plug manufacture holes in engines, AKA FREEZE PLUGS, something like this:

http://www.mbca.org/sites/default/files/7009016_FreezePlug.JPG

If something like that is used, then just make sure to use a fuel resistant material.

If a a center bolt is used, a gasketing washer would be needed to minimize gas leakage and gas fume leakage around the bolt.

To build on this idea... one could use the top of the existing boot as the gasket. Cut it so that the crosscut profile looks like an upside down "U". Now take the metal and put a lip around it like a jar lid (building from Farrar's post) so that it stays centered over the gasket. This is where a little adhesive would help to hold the two pieces together.

If the adhesive works well then the bolt is not needed (and maybe not the lip as well). Simply hose clamp the gasket to the tank lip like it is today.

Another method, which I'm still lukewarm on, is to bolt through the top part of the upside down "U" gasket through the metal disk to secure the two. This would still need sealant between the gasket and the metal plate. And the screws might pull through the rubber boot material... A metal ring inside the upside down "U" would minimize tear-through.

The more I think about this the more options...

Cut the existing boot so that it looks like an upside down "J" with the longer leg inside the tank. Use angle brackets with one leg against the gasket and the other the top. Use sealant between the metal top and the top of the "J" gasket. To prevent gasket pull-through a flat metal band could encircle the boot where the screws/rivets go through. The top could be spot welded or bolted (use sealant) to the brackets

BTW ... if metal is used for the seal/cover, the pump's electrical ground connection could use the metal (in other words, no electrical isolation from the metal seal. Then only one wire would need to pass through the tank wall. But... when removing the tank cover, the electrical connection may hinder its removal).

NK

Reminder: I'm "subject to being wrong without notice." ;)

nkemp

10-14-2011, 12:57 PM

I measured the opening ID: fuel pump hole in the gas tank = 100mm/3.94"

As such we need a 4" bung.

BUT (pun intended) ... This would press up against the metal bracket holding the pump (the metal bracket we use today). So you have rubber pushing agaist the metal that pushes against the tank plastic. It will leak between the metal and tank plastic without another gasket.

Thus I think mounting to the outside would work better.

nkemp

10-16-2011, 12:44 PM

After talking this through and some other ideas on the web, I drew up the diagram attached (used Paint.net. Free & easy to use...Visit CNET for DnLd) ... Image not to scale

The BLUE ring may not be needed if the plate retaining bolts could tap into the tank. The trouble is relative to sealing off the bolts so there is no gas leakage. Could use RivNuts :-( or epoxy, RTV the barbless version of the 2nd image ... blind nut. Size bolts so that they do not go through the epoxy/RTV.

Thoughts?

Is there any reason to believe that the pump could not be fully submerged in the tank?

Nick

sean

10-16-2011, 12:49 PM

Bitsyncmaster

10-16-2011, 12:56 PM

Most RTV and epoxy does not stand up well staying wet in gasoline and alcohol.

The fuel pump has not problems being submerged in gas. It will keep it running cooler.

robvanderveer

10-16-2011, 12:58 PM

I saw your diagram, personally I don't like 12v hot wire running through my fuel tank. Other than that i like these suggestions.

nkemp

10-16-2011, 01:29 PM

Most RTV and epoxy does not stand up well staying wet in gasoline and alcohol.

Homebuilt aircraft have been making fiberglass tanks for years. Are we talking about the same "epoxy"

Rather than plumb through the tank itself why not run the plumbing through your metal/plastic plate at the top? You could weld the fittings in place and not deal with hoping epoxy or RTV will seal it to the plastic tank.

The RV/Epoxy would be for the nuts through the tank to hold the top plate. I want the top plate to be removable for service WHEN the pump fails ... and it will.

The main reason for going through the tank(using purpose designed through tank fittings) is to make it easier to service the tank & pump. Gets them out of the way and no need to disconnect when opening the tank.

Nut see the next post ....

Nick

Ron

10-16-2011, 01:47 PM

Rather than plumb through the tank itself why not run the plumbing through your metal/plastic plate at the top? You could weld the fittings in place and not deal with hoping epoxy or RTV will seal it to the plastic tank.+1 !

Tangent: Don't tell Bill this but, when I was considering putting a carb on my D, I was thinking about a plate/cap with a single hole/fitting for a fuel line running to a rail mounted pressure regulated pump -- (Wires are outside and no return needed...You set the pumps cutoff pressure slightly above the carb's needle-seat pressure requirements but below the pump's bypass pressure and it will last ~forever.)

nkemp

10-16-2011, 01:50 PM

The GM units have intrigued me for some time. I took home the unit from the Astro when it failed. There are a couple variations and look like the photo.

The top has an in, out & vent port. All wires use the top plate.6038

As it turn out, when the gasket (not shown) is used they are near perfect fit. The trouble is that they are spring loaded (Up/DN) and when compressed they do not fit in the tank. When the springs are removed, they should fit.

BUT... the problem is still how to hold the top plate down. Again, something like the ring in the diagram is needed (on standard applications there is a threaded or lock ring retaining the unit).

Servicing this unit is easy since everything is attached to the assembly (including the fuel sender (not D compatible resistance))

They have great sumps that have back-flow valves so that the sump level remains after the pump stops. Corner hesitation should be eliminated with the GM design. Some suck the fuel from the sump, others suck from the tank bottom (preferred for max fuel availability) There may be other Mfr's that would work but I have not seen them up close and personal.

What I do not know about this pump assembly is the pressure & flow curves. What is the flow at D required pressures? Or would we need to strap the D's pump to the outside of the assembly with some replumbing?

Nick

Ron

10-16-2011, 02:12 PM

What I do not know about this pump assembly is the pressure & flow curves. What is the flow at D required pressures? Or would we need to strap the D's pump to the outside of the assembly with some replumbing?

NickThat pump is about 10psi too low.

If you are considering mounting any pump extrernally, see two posts up ;-)

nkemp

10-16-2011, 02:18 PM

All the pressure & flow info I could find was after the pressure regulator on GM vehicles. 10PSI low at the pump?

Close but no cigar,

Nick

Ron

10-16-2011, 02:43 PM

Yeah they are looking for 66psi in tests (1999 4.2 TBI...they dump the unused back). We have a check value of 71-79.7psi. I'm sure they are capable of more but too close for me... IIRC my D pump was closer to 90psi true pressure.
If you surf around, you can probably find a better one. I can pull the OEM data on one if it looks right but don't give the pressure data for you.

LEVY

10-16-2011, 02:52 PM

Most, if not all modern vehicles, have 12V running inside the fuel tank! But.....

The setting have been designed by professionals.

I saw your diagram, personally I don't like 12v hot wire running through my fuel tank. Other than that i like these suggestions.

sean

10-16-2011, 06:30 PM

The GM units have intrigued me for some time.

Nick
FYI, it seems DMCH may be interested in the same thing. Kevin Abato posted (http://www.facebook.com/media/set/?set=o.149133008431111&type=1) these gems to FB:
6039
6040
http://a4.sphotos.ak.fbcdn.net/hphotos-ak-snc7/s720x720/307516_10150360487487948_806842947_8140778_1893594 947_n.jpg
http://a2.sphotos.ak.fbcdn.net/hphotos-ak-ash4/s720x720/299049_10150360488267948_806842947_8140785_3172791 91_n.jpg
It seems they have a pump/sender assembly in the works.

nkemp

10-16-2011, 07:33 PM

Great minds think alike. :-)

I'll be interested in seeing how they secure the pump to the hole.

From the photos I can't tell if their pickup is inside the sump or outside (we want the latter).

Also, what pump are they using?

Bitsyncmaster

10-16-2011, 07:54 PM

Homebuilt aircraft have been making fiberglass tanks for years. Are we talking about the same "epoxy"
Nick

The experimental aircraft tanks are sealed with a "slosh" sealer. Only epoxy that comes close to gas proof is vinylester. But even then that's with aviation fuel that has no ethanol.

nkemp

10-17-2011, 10:20 AM

In terms of using plastic exposed to gas... gas cans are made of high-density polyethylene (HDPE)...#2 recycle code. On chemical resistance chart HDPE did not get the top rating but it seems to be working for gas can mfr's.

nkemp

10-18-2011, 11:55 AM

Here is an updated option. To simplify, a plug is secured inside the boot (which is cut like in inverted "J") and is held with a hose clamp. So now the boot hole is plugged and the seal around the tank top is as is today using the boot. Thus a sealed tank without drilling a bracket. A rain cover of some sort is needed to prevent water pooling in the boot (but if it does there are no parts to damage).

Buildup of vertical heights may be an issue.

DMCVegas

10-21-2011, 07:02 PM

Just to kind of chime in here, I too have always thought about a solution to this issue as well. I've had an idea for some time now about how to do this as simply, and cheaply as possible. Here goes.

The retrofit would only be of 3 off the shelf parts, and 3 custom pieces that can easily and cheaply be molded out of plastic. These pieces would replace the Fuel Pump Boot, the Fuel Pump Cover Seal, and the Fuel Pump Support Ring. That alone is over $100 worth of parts, and I'm sure we can go cheaper.

The first piece is a new Support Bracket. It will hold both the fuel pump, as well as the metal Return line. What I'm picturing is a cylinder that has an opening on one side, that allow the Return Line & Fuel Pump to be put snugly inside of it, as well as a molded support on the bottom to keep the pump exactly at the correct height from now on. Finish securing both items with a Hose Clamp or two. The top of this Bracket has a 90° flange that runs all around the edge so that you can mount/suspend it to/from the tank.

The Second piece is a ring that goes around the existing opening in the tank where the fuel pump goes. Except that it's threaded on the outside. This piece would have to be welded to the tank somehow. Most likely with epoxy which shouldn't be a problem since they do make gasoline resistant glues.

The Third piece would be a locking nut that would attach to the now-threaded opening to hold everything in place.

The 3 other off the shelf items would be 1 Gasket to seal the assembly to the tank, 2 rubber boots to cover the submerged terminals on the fuel pump. If on the Bracket we molded in a small boxed area on the top with 4 sides, and then had two holes at the bottom where the fuel pump wires passed through, we could then just shoot a small gob of Instant Gasket in to the niche to seal it up.

Now I honestly think that this is a viable way to retrofit the existing assemblies that we currently use. And no, having wires running into the tank does not pose a fire hazard. The fuel pumps we use now internally expose gasoline to electrical leads. Fuel acts as a coolant. But to have fire you need 3 things: Heat, Fuel, and Oxygen. And there is no oxygen present in liquid fuel nor fuel vapors. Volvo has been doing this for years with the wires in the tanks and never had a problem. So this is quite doable.

However, as much as I beleive that this is viable, I honestly don't know if it, or ANY other method of retrofitting the Fuel Pump assembly for that matter is actually *practical*. Two big questions:

Is this a cheaper/easier/more efficient way to accomplish what we already have?
Would people actually buy this? Would they be too scared to modify their cars? Do they not WANT to modify their cars for the sake of originality?

Here is an updated option. To simplify, a plug is secured inside the boot (which is cut like in inverted "J") and is held with a hose clamp. So now the boot hole is plugged and the seal around the tank top is as is today using the boot. Thus a sealed tank without drilling a bracket. A rain cover of some sort is needed to prevent water pooling in the boot (but if it does there are no parts to damage).

Buildup of vertical heights may be an issue.

The problem with that design is there there is no way for the fuel on the outside of your Sump to refill it once the outer fuel level passes below that line. That's why you have to use a Baffle. You could keep it that high to try and maintain a constant submergence with the fuel from the return line, but I don't think it needs to be quite THAT high. Mostly though with the smaller Baffle we currently use, it's supposed to keep only the intake filter for the pump submerged, which is all you really need.

nkemp

10-21-2011, 09:42 PM

The problem with that design is there there is no way for the fuel on the outside of your Sump to refill it once the outer fuel level passes below that line. That's why you have to use a Baffle. You could keep it that high to try and maintain a constant submergence with the fuel from the return line, but I don't think it needs to be quite THAT high. Mostly though with the smaller Baffle we currently use, it's supposed to keep only the intake filter for the pump submerged, which is all you really need.

The GM sumps (or equivalent) allow fuel to flow into the sump from the bottom and has backflow valves to prevent the fuel from getting out. With fuel from the return line the sump will be a higher level than the fuel tank (until it reaches the sump overflow). The problem with the GM units is that the pumps appear to not pump at the pressure and volume required of the Bosch CIS.

Some of the GM units pump from the sump bottom, some from the tank bottom. The latter can use more of the fuel in the tank.

You are correct relative to power lines in the fuel tank. If you are driving a car made in the last 10 or 15 years there is a good chance that the power lines are in the fuel. A solid connection eliminates the chance for a spark, gasoline is an excellent insulator and there is insufficient oxygen for combustion. The only real reason for the connector boot is in the event that something conductive got in the tank (like foil) and it got across the pump terminals, then there would be a spark opportunity. FWIW, some (maybe all) modern fuel pumps pump the fuel through the pump to cool it and in doing so expose the electrical to the fuel.

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. But to get the sump you'll need to do some junk yard work ... but that is kinda fun and entertaining.

To optimize this design we need the mfr of the existing boot to make a "flat top boot" or a domed one with no holes.

Nick

The Second piece is a ring that goes around the existing opening in the tank where the fuel pump goes. Except that it's threaded on the outside. This piece would have to be welded to the tank somehow. Most likely with epoxy which shouldn't be a problem since they do make gasoline resistant glues.

The Third piece would be a locking nut that would attach to the now-threaded opening to hold everything in place.

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.

I have not checked yet but I'd guess that the current locking rings are pretty close to our tank opening's OD.

If a GM unit (or equiv) could be found with sufficient flow & pressure, then cutting off the current boot leaving sufficient overlap to the GM unit top may be sufficient to hold it in the tank (Adding a bit of sealant (no rtv) would help).

I've poked at my failed Astro Gm unit for a couple years and have not come up with anything acceptable.

FWIW, true GM units are relatively expensive and look-a-likes don't necessarily perform as well or as long.

Nick

Bitsyncmaster

10-22-2011, 06:47 AM

With fuel from the return line the sump will be a higher level than the fuel tank (until it reaches the sump overflow).Nick

Explain to me how the return line will fill a sump?

The pump pulls fuel out of the sump. The engine uses some of that fuel. The excess is returned via the return line. So wouldn't the sump get drained of fuel?

DMCMW Dave

10-22-2011, 08:02 AM

Explain to me how the return line will fill a sump?

The pump pulls fuel out of the sump. The engine uses some of that fuel. The excess is returned via the return line. So wouldn't the sump get drained of fuel?

Yes, yes it would.

The GM pump has a hole in the bottom with a check valve to let fuel come in but not run out. So the level in the sump will be the same as the level in the tank. Maybe higher (due to fuel slosh) but not lower.

nkemp

10-22-2011, 09:48 AM

Explain to me how the return line will fill a sump?

The pump pulls fuel out of the sump. The engine uses some of that fuel. The excess is returned via the return line. So wouldn't the sump get drained of fuel?

Eventually yes. But the combination of the fuel flowing in via the valves on the bottom and the return fuel keeps the level higher than the tank level (once it gets below the sump overflow). Also, depending on the pump arrangement, it appears that some pumps pull from the sump and others pull from the tank bottom and the sump. I would prefer the latter for a D and wouldn't care if the tank had a "pump well".

Nick

... but a remind everyone that "I'm subject to being wrong without notice :goatee:

Bitsyncmaster

10-22-2011, 10:12 AM

Eventually yes. But the combination of the fuel flowing in via the valves on the bottom and the return fuel keeps the level higher than the tank level (once it gets below the sump overflow). Also, depending on the pump arrangement, it appears that some pumps pull from the sump and others pull from the tank bottom and the sump. I would prefer the latter for a D and wouldn't care if the tank had a "pump well".

Nick

... but a remind everyone that "I'm subject to being wrong without notice :goatee:

It will never fill above the tank level (not counting sloshing of the gas). Physically impossible since less gas is returned than the gas removed.

nkemp

10-22-2011, 10:33 AM

I would argue (respectfully... of course) that the combination of fuel inflow via the valves (simple rubber diaphragms) and the pump return allows the sump level to be above the tank level.

Or think of it this way, the level in the sump is consistent with the level outside the sump because of the valves on the bottom of the sump. Now add the return flow and the level rises.

Note that in most operation relative to the D, this is not particularly important until the tank level gets low or when the fuel moves to another part of the tank such as taking a curve or going up/down a steep incline. In those cases having the sump level higher than the tank level helps prevent fuel starvation.

The original D pickup design was supposedly a sump design (not a baffle as often discussed), albeit it a shallow sump. At least that is how a previous employee at DMCH explained it to me. Supposedly the original design would pump a tank substantially drier than a baffle design can accomplish.

Nick

Bitsyncmaster

10-22-2011, 10:54 AM

nkemp

10-22-2011, 11:34 AM

Maybe your right.

I made a mistake once ... I thought I was wrong ...but I wasn't :hysterical: Just kidding!

If you take a look at the GM units they are rather interesting. On one I have, there are two tubes coming off the pump top, the larger feeds the engine. The smaller returns to the sump (But I'm not sure of the flow direction (to or from the pump)). That unit also has a float controlling another valve (rubber diaphragm). It is this unit that picks up the fuel from inside the sump. Trouble is that I don't know why or what those do or how the unit "works".

If you get a chance to look at one, do so. It is not like the good old days (1981) :-)

Nick
897

DMCMW Dave

10-22-2011, 11:38 AM

It will never fill above the tank level (not counting sloshing of the gas). Physically impossible since less gas is returned than the gas removed.

I'd argue this as well - Assume the car is sitting still (to avoid the "slosh" factor). The baffle should match the tank level as the check valve will let in gas to keep it level. ANY gas returning from the engine will make the baffle more full as fuel cannot go backwards through the check valve.

I believe that this design makes it less important where the sump is physically in the tank. I was worried at first as I was never a fan of moving the baffle forward under the pump. The GM design should not have an issue as the sump is much less "leaky" and much deeper than the DMC or any of the tunacan designs.

Bitsyncmaster

10-22-2011, 11:45 AM

Now you got me thinking. If the baffle level is just a fraction above the tank level then no fuel will flow into those one way valves. So I'm back to thinking it will not be higher than the tank level

DMCMW Dave

10-22-2011, 11:46 AM

Bitsyncmaster

10-22-2011, 12:00 PM

But the excess fuel from the engine will tend to "top off" the baffle.

I still don't see it. Remember the pump is drawing out of the baffle and returning less than it draws. If the baffle level is ever above the tank level than no fuel enters the baffle from the tank. So my thinking is the baffle will not get higher than the tank.

nkemp

10-22-2011, 12:08 PM

I'm sure flow rate through the pump and engine fuel consumption can be calculated and if not, measured... to determine how much fuel flows back to the tank. I suspect that even at high load the amount of fuel used is much less than pumped and as such the sump stays full. Until the sump is full, the pump (in addition to feeding the engine) is simply pumping from the tank into the sump. I also suspect that until the tank is empty (below the pickup) the sump is full to the overflow.

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:-)

Or think about what happens when the key is turned to run and the pump starts. It is building pressure and excess fuel is returned to the sump.

Nick
897

Bitsyncmaster

10-22-2011, 12:22 PM

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:-)

Or think about what happens when the key is turned to run and the pump starts. It is building pressure and excess fuel is returned to the sump.

Nick
897But there is your error. The input to the sump is not infinite. It would vary from large quantity with the sump low (below tank level) to zero at tank level.

DMCMW Dave

10-22-2011, 12:32 PM

But there is your error. The input to the sump is not infinite. It would vary from large quantity with the sump low (below tank level) to zero at tank level.

The (gravity) pressure from the tank will keep the sump at a minimum at the tank level through the check valve assuming the check valve offers low input resistance. ANYthing coming back from the engine is excess and can't run out, so it's a net adder over the tank level. I'd also hazard a guess that at idle and even cruising speed (other than hard acceleration) the gas returning to the tank is 80% or better of what the pump is removing from the tank. This actually would be pretty easy to test with the injectors in jars and using small measured tank and return containers.

So - yeah, with a low tank under hard acceleration the sump may drop below full, but under somewhat static conditions it will always be close to full and should never be below the tank level (of course under acceration with a low tank the tank level will be very low at the sump - which is my original concern with using a more open-bottom flat baffle positioned towards the front of the car).

We'll need to build a clear tank for a demo....:)

nkemp

10-22-2011, 12:33 PM

Let's look at this from a sequence of operations perspective:

To simplify, lets assume the tank is partially full and below the top of the sump and that the sump & tank are at the same level;

we start the car and the pump starts.
some fuel is removed from the sump
the removed fuel is "immediately" replenished through the backflow valves so that the tank & sump stay at the same level
excess flow occurs in the fuel lines and is returned to the sump
this excess fuel adds to the fuel level raising it above the tank level

because the sump is the same level as the tank and it can't flow out via gravity

So the combination of inflow through the valves and the returned flow raises the sump level.

The use of "infinite" may have been the wrong word even though it was qualified with "finite".

nkemp

10-22-2011, 12:38 PM

So - yeah, with a low tank under hard acceleration the sump may drop below full,

But the sump is "relatively" large and short of making hi G donuts for a while, it will take a bit to empty the sump.

We'll need to build a clear tank for a demo....:)

How about using some of that transparent aluminum they used in Star Trek?

Nick
897

nkemp

10-22-2011, 12:47 PM

Bitsyncmaster

10-22-2011, 01:02 PM

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

10-22-2011, 01:16 PM

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

10-23-2011, 01:05 AM

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.

:hmm:Me thinks :tongue:

DMCVegas

10-23-2011, 07:17 AM

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.

:hmm:Me thinks :tongue:

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:

http://www.delorean.com/store/images/PRODUCT/medium/110043.jpg

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

10-23-2011, 07:41 AM

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

10-23-2011, 07:42 AM

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:

http://www.rccrawler.com/articles/txtdiff/55.jpg

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. (http://en.wikipedia.org/wiki/Nevada) 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

10-23-2011, 09:32 AM

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?attachmentid=6096&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 :dunno: (maybe an error on my part there)

Ron

10-23-2011, 09:42 AM

Having reread it all, I officially choose to say, "Dave is right". :hihi2:

nkemp

10-23-2011, 11:50 AM

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

nkemp

10-23-2011, 12:28 PM

Maybe it is time for a "process check".

The original purpose of this thread was to create a better fuel pump, fuel pick-up & return installation. I, as the instigator, hate the current method. The preferred method keeps the cost reasonable (we all know that we can do anything with sufficient funds).

There has been good discussion on how the GM sumps work. The question discussed is if the GM unit's fluid level can be above the tank level. This discussion is pertinent to the original purpose since it relates to internal components and operation.

I think the consensus is that the GM unit can have a higher fuel level than the tank. If so, the discussion can go back to how we can secure it to the top of the tank and what components to use. A couple alternatives for securing to the top have been discussed (notably casting a thread and lock ring and re-purposing the existing boot).

If there is uncertainty relative to the GM sump level being above the tank fuel level, try this mind game...

The unit is plumbed so that 100% of the fuel returns to the sump. Will the sump be higher than the tank? A: Yes ( I presume we all agree here)

As above except we divert some percentage of fluid flow from going into the sump. Will the level in the sump be higher than the tank? A: Depends and is a function of inflow rates through the backflow valves and the percentage returned.

So let the discussion go on ........................

Nick

DMCVegas

10-23-2011, 12:58 PM

The unit is plumbed so that 100% of the fuel returns to the sump. Will the sump be higher than the tank? A: Yes ( I presume we all agree here)

Nick

No, I disagree. The fluid level in the Sump/Baffle can only be as high as the reserve level in the tank. You might have a "check valve" system that keeps fluid escaping, acting as a one-way baffle, but with out a secondary pump whose sole purpose is to keep the Sump/Baffle filled with fluid, it will never rise above the fluid level in the tank.

As such it's hard, if not impossible to to use a replacement baffle that is separate from what we have now if you're going to maintain the same volume of fluid for the pump to be submerged in. We cannot defy gravity and raise fluid levels without a secondary pump.

Even if we were to calculate in the amount of residual fluid left in the return line from the Primary Pressure Regulator all the way back to the return line and used a Sump with a Check valve to prevent leakage back into the tank it won't happen. Let's say you start the car up, the pump begins extracting fluid, the level drops, and then fluid in the gas tank flows in to replace whats missing. Fine. You'll then have an equally balanced fluid level between the inside and outside of the Sump. Even if we figure in the volume of fluid from the return line that RAISES the fluid level inside of the Sump, that gain is only temporary. With the engine consuming fuel, we have a deficit of fuel of what it removes versus what it returns. At the same time the fluid pressure INSIDE of the Sump is greater than the fluid pressure inside. Sure we've got check valves, to keep fluid from flowing out, but the higher hydraulic pressure inside will prevent fresh fluid from flowing in.

Thus while at start-up there may be an initial surplus of fluid inside of the sump, it's only temporary. The pump will simply extract this fluid and it will not be replaced until there is room for additional fluid from the outside to flow in. And it will automatically stop ones the fluid levels equalize.

So no, the Sump level will not be higher than the tank because that is impossible. They'll always be equal.

Ron

10-23-2011, 01:09 PM

FWIW
Before reading his post, I was thinking "a sump doesn't have check valves or holes here" and thought about asking about it but it didn't seem to be worth mentioning at the time oops-I should have...Sometimes ya step on one toe trying to miss another...
Afterwords, I only mentioned it as a suggestion for why he and I weren't on the same page (guessing he missed the last design upgrade/pic or ???)...Subtle indeeed!

Actually, I take credit for mudding it up...I should of said, "...but the later discussion was about a [proposed device] with sump/baffle* with check valves (not free flowing holes) and a return into the baffle[], after pointing out it was a baffle [since it sits on rather than below the bottom of the tank, in this case]".

No, I disagree. The fluid level in the Sump/Baffle can only be as high as the reserve level in the tank. You might have a "check valve" system that keeps fluid escaping, acting as a one-way baffle, but with out a secondary pump whose sole purpose is to keep the Sump/Baffle filled with fluid, it will never rise above the fluid level in the tank.
NOW we're on the same page!

(Add "except with KOEO and I'm right with you totally)

The question discussed is if the GM unit's fluid level can be above the tank level.
OK my mistake there...I thought you dave and dave were discussing the unit you were proposing. But I still think the equation you gave and the expansion on it indicates the level in the baffle will never raise above the tank level unless the pump is running and the engine is not.

nkemp

10-23-2011, 02:28 PM

Enough talk ... time to go to the lab (garage)

I ran a GM pump unit in a bucket of water to see what happens. Here are the results

When I put the GM unit in the water, the level inside and outside leveled
When I removed the partially full sump from the water it does not leak out (works very well!)
When I ran the pump with all water returning to the bucket, the level remained the same inside & outside (as best I could tell)
When I ran 100% of the water into the sump, the sump raised to the sump overflow level
With the sump full, I directed the water to the bucket (none to the sump). The sump level DID NOT DECREASE (This was not expected) It stayed as full as it can get.
I let the sump sit "off" for a while. The level stayed as full as it can get

I removed the gm unit from the water (With water in the sump) simulating a empty tank. With the pump running, the liquid gets pumped down to empty.

The sump level not decreasing when the return flow was directed to the bucket and not the sump was a surprise. I thought there would be a slight decrease but not returning to the tank's level. Balancing somewhere in-between.

And YES the sump level will get higher than the tank level... and stay there until the tank is empty.

Here is a crude diagram of the GM sump I used (there are other variations). It has a pickup screen that sits on the bottom of the tank, outside the sump (preferred).
6225

Nick
897

Bitsyncmaster

10-23-2011, 03:32 PM

Then that GM pump is drawing fuel from outside the baffle? Does it also release some of that outside draw into the baffle? It must be working like the two pumps DMCvegas suggested.

The ultimate set up would have four pumps. One drawing from each corner of our triangle shaped tank feeding into a baffle for our stock pump.

nkemp

10-23-2011, 04:29 PM

Then that GM pump is drawing fuel from outside the baffle? . Outside the sump :-) ...Yes until the outside is empty then it pumps from inside the sump which has a fuel level equal to the overflow.

Does it also release some of that outside draw into the baffle? I don't think so. The fuel level inside the sump does not change once it is full. There was no sign of fuel overflowing when pumping from the outside and no return to the sump.

I checked a few things out. Pumping water through everything makes it a little better when using your mouth to check flow direction and backflow valves.
- The valve in the bottom pickup screen prevents backflow from the sump to the tank.
- The pump has two inlets on the bottom, no internal backflow valves between the two. It appears the inlets are part of one chamber inside the pump(based on airflow tests (mouth) & air noise when testing)
- The 2nd inlet screen inside the sump does not have any backflow valves.

It is not clear why it pumps preferentially from the 1st/bottom inlet screen until the main tank is empty.

Nick

nkemp

10-23-2011, 06:01 PM

Did anyone look closely at the unit displayed at the DMCH open house to see how they were going to attach the top of the pump unit to the tank? Pictures would be great.

DMCVegas

10-23-2011, 06:19 PM

Enough talk ... time to go to the lab (garage)

<SNIP>

I ran a GM pump unit in a bucket of water to see what happens. Here are the results

When I ran the pump with all water returning to the bucket, the level remained the same inside & outside (as best I could tell)
When I ran 100% of the water into the sump, the sump raised to the sump overflow level
With the sump full, I directed the water to the bucket (none to the sump). The sump level DID NOT DECREASE (This was not expected) It stayed as full as it can get.
[COLOR=red][COLOR=black]I let the sump sit "off" for a while. The level stayed as full as it can get

And YES the sump level will get higher than the tank level... and stay there until the tank is empty.

Nick
897

OK, we already have a problem with this test. You can't recycle 100% of the fluid back into either the Sump nor the tank itself. You need to start reducing the amount that goes back into the Sump to truly simulate a real world environment since the engine consumes a certain amount of the fuel that is collected by the pump. So *technicly* you need to split return into two hoses, with a valve on one end simulating consumed fuel (just run that into another bucket).

Now, that's just as I would see a Sump with a check valve. To understand more, does anyone have a cross-section diagram of the GM Pump internals? Perhaps since I cannot see that, that's why I'm having a difficult time understanding your results.

nkemp

10-23-2011, 07:44 PM

Here is the thinking relative to the test...

If 0% of the fuel goes back to the sump and the sump does not loose level, then anything were some of the fuel goes back would only add to the level (until it reaches the overflow). 0% return is the worst case scenario or is an EXTREME load.
100% return is unrealistic during operation... but remember that when you fill the tank it will be filled higher than the sump and fills the sump to the max.
Based on the test, the only time it draws from the sump is when the tank is empty.
It is not relevant if the tank looses gas as it is consumed. Would it make any difference how the sump works if you left the car run at while filling with gas? (Not recommended)

I've never seen a cross section on the web (Other than the poor example I made). Also, I've never seen anything on the web that explains the units operation. And there are multiple designs some more confusing than others. But if someone has info I'd love to see it.

I encourage anyone interested to ask for a failed one from a GM repair center(or any service center). Tell them to break off the ports if they are concerned that you'll try to use it. From a junk yard they will likely charge you for one, especially if they have to remove it. Removing one is a challenge..on an Astro and other trucks you have to drop the tank at a minimum.

The test may not be perfect but it does generate usable data. I believe that it shows that the sump will operate at a higher fuel level than the tank fuel level.