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Tue Sep 26, 2017 2:39 pm

Anyone with experience with Rotopax venting? I have a 2 gallon Rotopax on back of vanagon. It expands on direct heat and collapses in cold. It does not leak yet however!

Rotopax says to occasionally open can to release pressure. This is fine, but sometimes I am away for hours and the thing is a balloon, maybe an inch thicker than usual. This constant size change must eventually cause failure.
Also, when expanded, I cannot unscrew from center mount, then in morning after cold night it is loose and rattles on the mount.

Some people claim that it should only be filled halfway to allow for expansion, yet others say fill it because the liquid doesn't expand as much. Opinions are great and welcome, but does anyone know which is true? I have been filling 3/4 full.

Rotopax does not recommend vent holes, but could that fix the problem? I'm thinking a small valve on top maybe in the handle? A pinhole to let the pressure escape then refill with air as it cools? I understand that a small amount of fuel would weep out, but I have had motorcycle tanks with holes in the cap that didn't seem to be a problem.

Sorry for the long question.
Thanks, Chris

Tue Sep 26, 2017 5:12 pm

The Rotopax fuel cells are neat but they have some design flaws as you have discovered.

It won't take much searching of this forum (or any other) to realize that consumer fuel storage products sold in North America are regulated in such a way as to make them poor performers, mostly due to venting and safety "features."

If you're going to continue to use Rotopax, keep the last 25% of capacity free for air. Air is compressible, and liquid is not--so keep space for air.

Also try building a cover for your Rotopax cells. It will make them less conspicuous (and thus reduce the chance for tampering or theft) and it will keep them cooler. I used a local sail maker to fabricate covers for my cans.

The smaller capacity and greater expense of Rotopax systems are why I stayed with Scepter cans. I cover mine to keep them inconspicuous and cooler.

kourt

Tue Sep 26, 2017 5:59 pm

I had a Rotopax failure. It ballooned so much that I could no longer stack 2 of them together. They did replace it at no cost. Then the replacement immediately leaked. They replaced that one at no cost. All in all I'm not impressed with their quality control & design. Great customer service,. expensive and crappy design.

Tue Sep 26, 2017 6:07 pm

the vapor pressure of gasoline will pressurize a container whether there is air (or headspace) or not. it will distend the same amount whether there is one cup or full with no air. PV=nRT. cannot change the laws of physics.

if you vent the pressure out, it will return very quickly as the liquid and gas phases come to equilibrium.

it is a design flaw whereby the plastic is of insufficient strength to overcome the vapor pressure. plastic containers can and do work, aka outboard motor tanks. but they are very thick and strong. steel cans work also. but the hardware store plastic gas cans swell up like an engorged wood tick in the sun. but hey, they're cheap, right?

i'm surprised the Rotopax are like that. thought they were strong as they are kinda spendy. bottom line is that gas containers have to be sealed with no venting so as to not drive off the essential volatiles and more importantly to not be a fire hazard.

-dan

Tue Sep 26, 2017 6:15 pm

Ive wondered how folks are storing cans on their roof and in bumper mounted carriers. Here in AZ even a metal can will warp and eventually leak. Painting it whites not gonna do it here.
Im at a loss for fuel storage and my gauge is not working.

Tue Sep 26, 2017 9:56 pm

My Rotopax were stacked together on the rear mounted spare tire, but under the tan colored Trasharoo, aka not in direct sunlight. The plastic is thick and seems tough, but it bloats in the heat.

Wed Sep 27, 2017 12:51 am

Federal emission laws in about 2009 ruined the gas can for all of us. :evil:
They no longer work, not one of them that I've ever purchased in recent years.

Where did these stupid rules originate???
In California!
Yeah...... no surprise there! Thanks California! :roll:

Dave

Wed Sep 27, 2017 6:07 am

djkeev wrote: Federal emission laws in about 2009 ruined the gas can for all of us. :evil:
They no longer work, not one of them that I've ever purchased in recent years.

Side note.. I've used my metal Wavian NATO style cans for 3 years now. They too expand and contract based on weather BUT they have never burst or leaked. I usually vent them when making drastic changes in elevation.

Paint has faded and is flaking off in some small wear spots but that's the only downfall so far.

I've heard stories of people who have had Rotopax cans burst, completely dousing them in fuel when trying to refuel their vans. Not good. Be careful.

Wed Sep 27, 2017 7:59 am

2-way venting valves have been around a long time, they could solve the whole problem by just adding one of these to the cap:
http://www.minivalve.com/newsite/index.php/en/by-t...-they-work

Unfortunately this particular company only sells to industry, because their products and the seat machining to use them is bone simple, but if someone can find a manufacturer that sells to individuals or in small lots, they could make a cottage industry of modified caps to solve this oh-so-simple problem.

Me, if I need more fuel, there's no way I would drive around with cans of gasoline mounted to the outside of my vehicle, I think that's insane. For me it's either a built-in tank within the crash structure, or better trip planning.

Wed Sep 27, 2017 9:59 am

tencentlife wrote: For me it's either a built-in tank within the crash structure, or better trip planning.

Coming soon from vanistan, custom larger gas tanks! ;-)

Wed Sep 27, 2017 10:05 am

bokonon42 wrote: tencentlife wrote: For me it's either a built-in tank within the crash structure, or better trip planning.

Coming soon from vanistan, custom larger gas tanks! ;-)

IF they were properly designed, easy to fill, have a fuel gauge and a quality fuel transfer system, yes, I'm sure they would sell.

It seems like everything I've seen falls short on one or more of the above points.

I think that adding a syncro styled filler location piped to a tank under the floor where the fuel pump is would be ideal.
Same side filling, "off the shelf" technology (if syncro filler parts are available??)

Dave

Wed Jul 24, 2019 7:43 am

DanHoug wrote: the vapor pressure of gasoline will pressurize a container whether there is air (or headspace) or not. it will distend the same amount whether there is one cup or full with no air. PV=nRT. cannot change the laws of physics.

if you vent the pressure out, it will return very quickly as the liquid and gas phases come to equilibrium.

If one cup, pressure will be "higher sooner" because the "same input of heat" will raise the smaller amount of fuel to a higher temperature "sooner". If there's one hour a day where it's in the sunlight then 1 cup will behave different than a full tank would.

But agreed; the same "steady state end pressure" is the same.

If gasoline were invented yesterday there's no way they'd let us "self-serve".

:idea: big safety IDEA :idea:
To increase your own gasoline safety you could pass by (decline to stop) at any gas station that has any motorist
,,,, (a person with unknown safety procedures) dispensing gasoline at that moment.

Problem is, then you'd need to carry a rotopax, thereby increasing your risk in a different way. :wink:

Unlikely anybody will adopt this great idea.....
but maybe the point comes across that we all know how dangerous gasoline can be, but there exist a major fuel-handling event every few days, that we are pretty cavalier about...
And pretty much.... nothing happens.
Vanagon maintenence status and expertise appears to be a far greater danger.

Wed Jul 24, 2019 8:02 am

there's two things at play here... the vapor pressure exerted by the evaporation of the gasoline AND the thermal expansion of the volume of gas. the thermal expansion is why you MUST leave some headspace in the container as the liquid is incompressible.

for example.. the using the expansion coefficient for gasoline, a 5 gallons of gasoline will expand by 0.2 gallons when it goes from 55F to 130F. this is uncompressible expansion that needs either headspace in the container or flex in the container to accomodate the increase in volume.

Wed Jul 24, 2019 8:02 am

HoustonPhotog wrote:
Side note.. I've used my metal Wavian NATO style cans for 3 years now. They too expand and contract based on weather BUT they have never burst or leaked. I usually vent them when making drastic changes in elevation.

On a recent long trip (~12k miles) I decided for reasons I won't get into to carry 2x 5gal wavian cans. I had need for them in a few different places far from services. Anyway it did not occur to me to stop and vent them and we carried them through climates ranging from high/cold to hot/low.

Wed Jul 24, 2019 11:25 am

I carry two 3.5gal Fuelpax on my swing away carrier and a 4gal Rotopax in the luggage rack (yeah, yeah, I know). I only use the 4gal if heading into the boonies, or if I want to really stock up on cheap gas before California ( :shock: ). A few times in South America having all 11 gallons of gas was definitely needed.

More to the point, my 4 gallon tank just started leaking. It developed a crack around the middle mounting point that expands and leaks when it gets hot. Starting a warranty claim for that one now.

I really hate the Rotopax, and the mounting (especially their fancy locking handle). They bloat too much to really secure them with the mounting, which makes the locking handle pointless. The lock also gets dirty/rusty and seized.

Still, Rotopax was the easiest way to go for the mounting location (GW swing away, above the spare tire) and amount of gas, despite being a PITA.

Wed Jul 24, 2019 12:12 pm

What about these?

https://www.agmcontainer.com/breather_valves/two_way

Thu Sep 29, 2022 8:00 am

Has anyone tried one of these spare tire tanks?

https://www.trailedonline.com/product-page/spare-tire-auxiliary-tank