Polyethylene fuel tank physics? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chaptr2 · 02-06-2003, 12:18 PM

Ok this is for the people who have installed or really know the physics of the fuel tank.

Right now I'm installing the fuel lines to my already installed polyethylene tank. I'm installing a BG220HR system and have all the fuel lines and most of the fittings to make it work.

My question is about the three ports on top of the tank (feed, return, and breather). I believe they are 1/4-inch holes (really small) two by the fill tube spout and one on the far side of the tank. Is the fuel sucked up to the top of the tank or is there a specific hole I'm supposed to use for the feed line? How does the fuel at the bottom of the tank get sucked up to the fuel lines?

I tried getting a mirror inside the tank this morning, but was not successful. Does anyone have any idea on how the physics of the system work?

chaptr2 · 02-06-2003, 12:26 PM

This is the pump I'm using.

chaptr2 · 02-06-2003, 12:32 PM

here is the way the system has to run.

da-burb · 02-06-2003, 02:29 PM

Fuel comes from the sending unit. Take a look at that and it will all become clear.

The things you are describing are, 1) fuel inlet (largest) 2)fuel inlet overflow return line which also lets air out as you fill up 3+4) left tank vent and right tank vent.

chaptr2 · 02-06-2003, 03:45 PM

Thank you!! I guess if I pulled the sending unit out of the box I would have seen that. That will make getting the fittings much easier. Thanks Da-burb.

da-burb · 02-06-2003, 09:39 PM

Now, you might look at adding a fuel return line to your sending unit. Drill a hole and add a piece of tubing, solder it in and away you go. I have heard of people using one of the vent ports as a fuel return line. I don't know if I would feel safe doing it that way. You would be driving a flame thrower if it ever slipped off while driving. Better to take a look at a modern fuel injected vehicle's sending unit and see how they routed the return tube.

UNCLEBOB · 02-07-2003, 04:23 AM

If the poly tank is under the truck and your going to race it I under stand you will have to make a sheetmetal cover for it. Im in that process now. good luck

chaptr2 · 02-07-2003, 03:14 PM

Thanks Da-burb that is a very good idea with the return line. I spent last night looking at all the possibilities of where the return will go. I will most likely go with vent tube for a return, but I will have to drill it out to 3/8. I don't want to adapt it down, because it is only a 1/4 hole that would really restrict fuel getting back in side the tank. I won't be using any hose clamps because I want to eliminate any possible leakage. This is all AN fittings with only two standard fittings with clamps.

Thanks Uncle Bob, I didn't know that. Is there a specific cover or thickness it has to be? It will be awhile before it hits the track, but any advanced notice is appreciated.

UNCLEBOB · 02-08-2003, 04:00 AM

I still have to ask ray the local tech guy on what gauge metal it needs to be. Ill let you know.

chaptr2 · 02-08-2003, 11:49 AM

Thank you for doing that. Is there any other surprises I should be aware of?

UNCLEBOB · 02-16-2003, 01:42 AM

Bottom of fuel cell must be covered with.024 steel or .032 aluminium sheet metal when fuel cell protrudes through floor. NHRA Rulebook

chevymad · 02-16-2003, 02:08 AM

One more thing, on an eletric fuel pump system where the fuel is constantly flowing back to the tank via the return, the return line should exit within 2" of the bottom of the tank. Dont just dump the fuel in the top of the tank. Especially with a plastic tank. The fuel falling inside will build up a static electric charge. If it should discharge you can blow the tank up!! This is the same reason why you shouldnt fill poly gas cans in a pickup bed.. or regular gas cans on a poly bed liner!

02-06-2003, 12:18 PM	#1
chaptr2 Registered User Join Date: Mar 2000 Location: Olalla, WA Posts: 705	Polyethylene fuel tank physics? Ok this is for the people who have installed or really know the physics of the fuel tank. Right now I'm installing the fuel lines to my already installed polyethylene tank. I'm installing a BG220HR system and have all the fuel lines and most of the fittings to make it work. My question is about the three ports on top of the tank (feed, return, and breather). I believe they are 1/4-inch holes (really small) two by the fill tube spout and one on the far side of the tank. Is the fuel sucked up to the top of the tank or is there a specific hole I'm supposed to use for the feed line? How does the fuel at the bottom of the tank get sucked up to the fuel lines? I tried getting a mirror inside the tank this morning, but was not successful. Does anyone have any idea on how the physics of the system work? __________________ This is only my opinion and it is subject to change. 70 GMC Short box stepside Blown 388 Stroker 72 K/5 Blazer 350/SM465/205

02-06-2003, 12:26 PM	#2
chaptr2 Registered User Join Date: Mar 2000 Location: Olalla, WA Posts: 705	This is the pump I'm using. Attached Images __________________ This is only my opinion and it is subject to change. 70 GMC Short box stepside Blown 388 Stroker 72 K/5 Blazer 350/SM465/205

02-06-2003, 12:32 PM	#3
chaptr2 Registered User Join Date: Mar 2000 Location: Olalla, WA Posts: 705	here is the way the system has to run. Attached Images __________________ This is only my opinion and it is subject to change. 70 GMC Short box stepside Blown 388 Stroker 72 K/5 Blazer 350/SM465/205

02-06-2003, 02:29 PM	#4
da-burb "Ochre Ogre" Join Date: Apr 2000 Location: Springfield, MN Posts: 3,558	Fuel comes from the sending unit. Take a look at that and it will all become clear. The things you are describing are, 1) fuel inlet (largest) 2)fuel inlet overflow return line which also lets air out as you fill up 3+4) left tank vent and right tank vent. __________________ Bowtie Truck Stop Inc. Mid-West GM Truck Restoration Parts Supplier Your Key Parts, Auto Metal Direct, Dynacorn, and Goodmark dealer. like us @ www.facebook.com/BowtieTruckStop 1971 C-10 Suburban (Ochre) 1971 K-10 Suburban (Ochre) 1972 C-10 Suburban (Ochre) 1972 K-20 Suburban (Yellow- that just aint right!) Springfield, Minnesota 56087

02-06-2003, 03:45 PM	#5
chaptr2 Registered User Join Date: Mar 2000 Location: Olalla, WA Posts: 705	Thank you!! I guess if I pulled the sending unit out of the box I would have seen that. That will make getting the fittings much easier. Thanks Da-burb. __________________ This is only my opinion and it is subject to change. 70 GMC Short box stepside Blown 388 Stroker 72 K/5 Blazer 350/SM465/205

02-06-2003, 09:39 PM	#6
da-burb "Ochre Ogre" Join Date: Apr 2000 Location: Springfield, MN Posts: 3,558	Now, you might look at adding a fuel return line to your sending unit. Drill a hole and add a piece of tubing, solder it in and away you go. I have heard of people using one of the vent ports as a fuel return line. I don't know if I would feel safe doing it that way. You would be driving a flame thrower if it ever slipped off while driving. Better to take a look at a modern fuel injected vehicle's sending unit and see how they routed the return tube. __________________ Bowtie Truck Stop Inc. Mid-West GM Truck Restoration Parts Supplier Your Key Parts, Auto Metal Direct, Dynacorn, and Goodmark dealer. like us @ www.facebook.com/BowtieTruckStop 1971 C-10 Suburban (Ochre) 1971 K-10 Suburban (Ochre) 1972 C-10 Suburban (Ochre) 1972 K-20 Suburban (Yellow- that just aint right!) Springfield, Minnesota 56087

02-07-2003, 04:23 AM	#7
UNCLEBOB Registered User Join Date: May 2000 Location: bremerton wa 98310 Posts: 100	If the poly tank is under the truck and your going to race it I under stand you will have to make a sheetmetal cover for it. Im in that process now. good luck __________________ 68 lwb 383 solid roller,250dur, 582lift, afr 210s, 10.8 comp. edel.rpm, 750vs,1 3/4 headers turbo 400, 3500 stall,ford 9 inch 3.89 gears

02-07-2003, 03:14 PM	#8
chaptr2 Registered User Join Date: Mar 2000 Location: Olalla, WA Posts: 705	Thanks Da-burb that is a very good idea with the return line. I spent last night looking at all the possibilities of where the return will go. I will most likely go with vent tube for a return, but I will have to drill it out to 3/8. I don't want to adapt it down, because it is only a 1/4 hole that would really restrict fuel getting back in side the tank. I won't be using any hose clamps because I want to eliminate any possible leakage. This is all AN fittings with only two standard fittings with clamps. Thanks Uncle Bob, I didn't know that. Is there a specific cover or thickness it has to be? It will be awhile before it hits the track, but any advanced notice is appreciated. __________________ This is only my opinion and it is subject to change. 70 GMC Short box stepside Blown 388 Stroker 72 K/5 Blazer 350/SM465/205 Last edited by chaptr2; 02-07-2003 at 04:41 PM.

02-08-2003, 04:00 AM	#9
UNCLEBOB Registered User Join Date: May 2000 Location: bremerton wa 98310 Posts: 100	I still have to ask ray the local tech guy on what gauge metal it needs to be. Ill let you know. __________________ 68 lwb 383 solid roller,250dur, 582lift, afr 210s, 10.8 comp. edel.rpm, 750vs,1 3/4 headers turbo 400, 3500 stall,ford 9 inch 3.89 gears

02-08-2003, 11:49 AM	#10
chaptr2 Registered User Join Date: Mar 2000 Location: Olalla, WA Posts: 705	Thank you for doing that. Is there any other surprises I should be aware of? __________________ This is only my opinion and it is subject to change. 70 GMC Short box stepside Blown 388 Stroker 72 K/5 Blazer 350/SM465/205

02-16-2003, 01:42 AM	#11
UNCLEBOB Registered User Join Date: May 2000 Location: bremerton wa 98310 Posts: 100	Bottom of fuel cell must be covered with.024 steel or .032 aluminium sheet metal when fuel cell protrudes through floor. NHRA Rulebook __________________ 68 lwb 383 solid roller,250dur, 582lift, afr 210s, 10.8 comp. edel.rpm, 750vs,1 3/4 headers turbo 400, 3500 stall,ford 9 inch 3.89 gears

02-16-2003, 02:08 AM	#12
chevymad Registered User Join Date: Jan 2001 Location: skamokawa, WA, USA Posts: 527	One more thing, on an eletric fuel pump system where the fuel is constantly flowing back to the tank via the return, the return line should exit within 2" of the bottom of the tank. Dont just dump the fuel in the top of the tank. Especially with a plastic tank. The fuel falling inside will build up a static electric charge. If it should discharge you can blow the tank up!! This is the same reason why you shouldnt fill poly gas cans in a pickup bed.. or regular gas cans on a poly bed liner!



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