Auxiliary Fuel Tank for Travel

[Buster Hymen]

FatMax use to make an auxiliary tank that sat where the faux tank sat.

 

[redbaron13]

One of the guys on here or the v4 forum used a small beer keg which he attached to a rack on the rear fender. However, in a rear end collision there may be a possibility of the keg lighting your fire, so to speak.

 

[fuup]

This is exactly what I've been considering but, in the videos I've seen everyone is connecting to the vent tube at the filler neck and that makes no sense to me. Unless I'm understanding it wrong, the vent/breather tube is to allow air into the tank to replace the fuel that is consumed and to allow for the release of gasses during heat expansion. If you use this tube as your filler there is nowhere for the air to go when you fill it up. Obviously, it appears to be working for people but, I'm not understanding why? Thoughts?

Well, you should be able to just add a breather on the secondary tank. Since they'd be directly connected it's all functionally the same unit.

It doesn't have to be the most efficient thing, since it'll drain all the gas in the auxiliary tank way faster than you'd burn it. I guess in theory, since gas and fuel would be moving opposite directions in the same line, air bubbles could get stuck in it here and there but I imagine the vacuum would clear them out before they were ever an issue. I think for the sake of safety you'd want to run the breather hose directly into the stock breather hose though, as to avoid any risk of spillage in a drop. In theory you wouldn't even need a breather hose as long as there's some sort of hole lol.

But yeah, it'd go something like

gravity feed from aux tank on luggage rack or back seat (as long as it's above the gas tank) > original breather
breather from aux tank > original breather hose

At the end of the day, all the breather is is a hole. Functionally it's not any different than the hole the gas typically goes out of (with the exception of the breather being where the gas doesn't go, usually on top of a tank) so I can't see why it wouldn't be able to take fuel in the same way it equalizes pressure by taking in or releasing gas.

I hope that cleared up the concept a bit.

 

[sdt354]

If I bolt a tank/bottle on, it's going to be filled with nos.

 

[Turbo Ghost]

Well, you should be able to just add a breather on the secondary tank. Since they'd be directly connected it's all functionally the same unit.

It doesn't have to be the most efficient thing, since it'll drain all the gas in the auxiliary tank way faster than you'd burn it. I guess in theory, since gas and fuel would be moving opposite directions in the same line, air bubbles could get stuck in it here and there but I imagine the vacuum would clear them out before they were ever an issue. I think for the sake of safety you'd want to run the breather hose directly into the stock breather hose though, as to avoid any risk of spillage in a drop. In theory you wouldn't even need a breather hose as long as there's some sort of hole lol.

But yeah, it'd go something like

gravity feed from aux tank on luggage rack or back seat (as long as it's above the gas tank) > original breather
breather from aux tank > original breather hose

At the end of the day, all the breather is is a hole. Functionally it's not any different than the hole the gas typically goes out of (with the exception of the breather being where the gas doesn't go, usually on top of a tank) so I can't see why it wouldn't be able to take fuel in the same way it equalizes pressure by taking in or releasing gas.

I hope that cleared up the concept a bit.

Ok, I just rewatched a video of a custom aux tank set-up and it feeds into the vent tube and then there is a vent coming off the aux tank which ties into the original vent hose. This all matches up with your explanation but, I'm just having trouble with the thought of the gas cap actually holding back the head pressure from the aux tank! With a full aux tank that's got to be a foot of elevation. Are the caps that secure and sealed? Thanks for your response!!

 

[fuup]

Ok, I just rewatched a video of a custom aux tank set-up and it feeds into the vent tube and then there is a vent coming off the aux tank which ties into the original vent hose. This all matches up with your explanation but, I'm just having trouble with the thought of the gas cap actually holding back the head pressure from the aux tank! With a full aux tank that's got to be a foot of elevation. Are the caps that secure and sealed? Thanks for your response!!

I would imagine as long as it's designed to be an auxiliary gas tank to be used in such a way you won't have any issue with it. A lot of them are made for ATV's and the like, so they'd be pretty well made I think.

 

[Turbo Ghost]

I would imagine as long as it's designed to be an auxiliary gas tank to be used in such a way you won't have any issue with it. A lot of them are made for ATV's and the like, so they'd be pretty well made I think.

I don't think I was clear enough on my issue. My concern is with the cap on the MAIN tank! You've got the pressure from the aux tank pushing against it and as I stated before, obviously it's working for people but, I would never have thought that cap was sealed that well to withstand a good foot or so of head pressure. Does that make more sense?

 

[crynool]

I don't believe this is an issue. The pressure coming from the second tank is only the gravity feed, coming from a small fuel line.

I could imagine, the pressure built up inside, full tank, the bike sitting in the sun is much more.

 

[fuup]

I don't think I was clear enough on my issue. My concern is with the cap on the MAIN tank! You've got the pressure from the aux tank pushing against it and as I stated before, obviously it's working for people but, I would never have thought that cap was sealed that well to withstand a good foot or so of head pressure. Does that make more sense?

Ooooh. I get you now, sorry. Yeah I mean I can't *guarantee* it won't be an issue, same as I can't guarantee the sun will come up tomorrow, but it's not something that will concern me in the slightest personally.

 

[Turbo Ghost]

I don't believe this is an issue. The pressure coming from the second tank is only the gravity feed, coming from a small fuel line.

I could imagine, the pressure built up inside, full tank, the bike sitting in the sun is much more.

Yes, but the pressure would be gaseous and relieved by the vent tube. As for the small fuel line, head pressure is determined by the height of the liquid column not volume or line diameter.

 

[Turbo Ghost]

Ooooh. I get you now, sorry. Yeah I mean I can't *guarantee* it won't be an issue, same as I can't guarantee the sun will come up tomorrow, but it's not something that will concern me in the slightest personally.

Ok, I did what I should have done in the first place. I did the math! If the height of the liquid column is 12" then the pressure at the vent tube would be a little over .3psi. Way less than I would have thought! That explains why it seems to be working for those who have done the mod! I don't know about you guys but, I feel better!

 

[crynool]

I was thinking about p = F / A, doesn't it apply? smaller line = smaller Area, less Force?

 

[D Larson]

I was thinking about p = F / A, doesn't it apply? smaller line = smaller Area, less Force?

That is correct but the pressure due to the column of fluid is given by P=density * gravity * height of the fluid

 

[Turbo Ghost]

Be careful guys! If outsiders start seeing posts like these they'll start thinking Vmax riders are smart!

 

[crynool]

That is correct but the pressure due to the column of fluid is given by P=density * gravity * height of the fluid

Got it. if the concern is that the height of the fluid impacts that much, add a fuel pump and activate only when <90% in the main tank....
But I still cannot believe that the small height and the small amount of fuel (2.5 gallon?) creates such an impact (No, I did not look to the numbers, just coming from my tummy )

 

[crynool]

Be careful guys! If outsiders start seeing posts like these they'll start thinking Vmax riders are smart!

People who know me will NEVER think this....

 

[Turbo Ghost]

Got it. if the concern is that the height of the fluid impacts that much, add a fuel pump and activate only when <90% in the main tank....
But I still cannot believe that the small height and the small amount of fuel (2.5 gallon?) creates such an impact (No, I did not look to the numbers, just coming from my tummy )

If you were to use a pump in the way you are referencing you are right back to my original confusion. That pump would be in the line that was formerly the vent tube which means the main tank has no way to vent or replace the volume that is lost during fuel consumption. Having the whole system filled and venting the aux tank solves that problem. As for the head pressure, a simple tube of fuel of say 1/2"DIA X 3' tall would have the same head pressure as a 100 gallon tank that is only 3' tall with a 1/2"DIA tube coming out the bottom. Volume and diameter have no effect on head pressure, only the vertical height. That's why you see water tanks for flat-land towns that are very tall with the round tank at the top so they can get the head pressure while in mountainous areas you will usually see wide, squat tanks for more volume and the terrain takes care of the height for head pressure.

 

[Turbo Ghost]

People who know me will NEVER think this....

Everyone I meet comments on how smart I am but, they always combine it with something about my posterior. Weird...

 

[schudaddie]

Hello! I recently got me a gen 2, and I absolutely love it. I'm sure y'all are aware of the relatively small range it has though. It really doesn't bother me for out carving pavement, but it certainly would be nice to get another couple of miles out of it in some "touring" scenarios. I was thinking about adding one of those sissy bar auxiliary tanks for about an extra 2 gallons of fuel. Seems like a significantly more simple solution than basically disassembling the thing to add a new fuel tank lol.

****** idea? I don't know haha. I imagine it's probably not the safest thing in the world in the event of a tip-over, but it would really only be for highway miles to add another 2 or 3 gallons. Anyone ever give it a shot?

Something like in the picture here:
View attachment 73097View attachment 73098

I was thinking that maybe I could run the gravity feed into the breather on the main tank and connect the breather on the aux tank to the original breather line. It would take a minute to add and remove but it wouldn't be harder than taking the seat off I think. I'm really talking out of my ass here, I'm not sure how functional that would be lol. It seems okay in my head...

Anyway, just some fun things to think about. Thanks.

looks like the one done on a gen1 back in 6/2015. read here......
https://www.vmaxforum.net/threads/tour-tank-setup.38212/later, bill

 

[crynool]

If you were to use a pump in the way you are referencing you are right back to my original confusion. That pump would be in the line that was formerly the vent tube which means the main tank has no way to vent or replace the volume that is lost during fuel consumption. Having the whole system filled and venting the aux tank solves that problem. As for the head pressure, a simple tube of fuel of say 1/2"DIA X 3' tall would have the same head pressure as a 100 gallon tank that is only 3' tall with a 1/2"DIA tube coming out the bottom. Volume and diameter have no effect on head pressure, only the vertical height. That's why you see water tanks for flat-land towns that are very tall with the round tank at the top so they can get the head pressure while in mountainous areas you will usually see wide, squat tanks for more volume and the terrain takes care of the height for head pressure.

Here kicked my stupidity in .... should not try to play with the big boys.
Yes, got you.
Anyway, do we THINK or do we KNOW if the head pressure to the cap is an issue for a 2.5 gallon tank?
When the pressure increases, (when the fluid expands due to i.e. heat), it will push the gasoline back to the secondary tank I believe, unless the head pressure caused by the secondary is >threshold. (I'm mixing two different topics now ) and there is no movement in the system (not running).
But let me ask a different thing, back to the fuel line.

When the engine runs and the secondary tank cannot deliver the same amount of fuel per minute what the engine is consuming, would mean, the main tank gets emptier over time, but there would not be much pressure to the main cap, as the main tank is not full unless the engine is not running, right or wrong?

So the diameter of the fuel line could be something to consider. *twisting head*