Helium-Is my tank really not refillable? Why don't ballloon animals float?

#1 Is the tank really non-refillable? #2 Balloon animals filled with helium do not float. Why?

A store near me has been going out of business for a month or so. I’ve been calculating how long I could wait before I had to grab an item. Today, the discount on the helium tank was 80%. I pounced.

There are several labels warning me that the tank is not refillable. Why not? We’re dealing with a non-flammable, non-toxic gas. The tank is fitted with a safety hatch. Surely there is easily available, cheap equipment to figure out the maximum safe pressure. Refilling has got to be cheaper than getting a new tank. Is there an actual danger, or is this a combination of planned obsolescence, and legally covering-your-butt?

Captain Visual (the greatest living balloon artist in the known universe) has written that balloon animals filled with helium will not rise. It’s the only time I’ve ever doubted him. I was wrong. A chihuahua filled with helium is no more bouyant than one filled with air. The Captain does not explain the physics behind this. I know one of the Dopers can.

PS- I am aware of the danger of inhaling helium directly from the tank. The nozzle will not be anywhere near my mouth, nostrils, ears, or other openings.

I never knew helium balloon animals would not float, but since you have tried it and confirm it - the reason is simple, you can’t get enough helium in the balloon to make it buoyant. It has an unfavorable surface area to volume ratio. The surface area is the balloon itself and the volume is of course the helium. A long skinny balloon already requires much more latex than a standard balloon to hold the same volume of helium. And to make it into a balloon animal you have to leave it partially filled in order to have enough room to tie it into it’s animal shape which further restricts the useable volume. So, no floating for your latex poodle.

As far as the refilling question, in order to be refillable, pressure vessels have to be able to withstand a certain amount of wear and tear over their lifetimes and require a pressure test every so often to prove that they are still safe at some percentage above their rated capacity. A refillable helium cylinder is of MUCH heavier construction than the standard throw-away variety. Also, in order to prevent a pecunious individual such as yourself from refilling it anyway, disposable pressure containers have a one-way valve. Helium goes out, but nothing goes back in. As to how they fill it in the first place, I can only guess.

Makes sense.

I was hoping to compensate by filling it to a lower pressure.

What would it take to remove that valve and install a two-way valve? I refuse to accept that when the helium runs out, this tank is no longer useful. What about some kind of ill-advised scuba apparatus? Or modifying the tank, adding some new parts and being able to spray epic amounts of whipped cream on my enemies*? At the very least, what about some bizarre Flash Gordon style helmet?

*This is not a veiled drug reference. I’d much rather be able to spray two cubic yards of whipped cream than do drugs. Just say no, folks.

If you bought a tank that loos like this one it is not refillable.
The problem is not with the helium, it’s with the tank. This style tank is not rated for refilling. If on the other hand your tank looks like one of these you should be able to get it refilled.
Guess which style is more expensive? :smiley:
Yes there is a danger. Tool companies used to sell a conversion kit to use old Freon (R-12) tanks as air tanks for filling tires etc. I have seen pictures where after a while the tank corroded from the inside and split when refilled. :eek:
You do not want be near a tank that splits during refilling.
Here is a SCUBA tank that failed. Need I say more?

What if I kept the pressure down to two or three atmospheres?

Ah well, it looks like it will have to be an art project. Am I going to need a torch to cut this thing?


It is highly unlikely that your disposable tank has a removeable valve. More likely than not it is welded in place. Besides which, there are no available two-way valves to replace it if it were removeable. And lastly, no place with the equipment to refill helium cylinders would touch it for legal reasons since it has not been pressure tested.

As far as the Flash Gordon headgear, I say go for it! But from my own experience at trying to turn an empty Freon tank into a small BBQ grill, it ain’t that easy. :slight_smile:

  1. I don’t know what the tank was rated for to start with. I hesitate to guess.

  2. Not hard at all to cut. A hacksaw would do it.

That just means when it blows you’ll lose a finger instead of an arm.

Trust me-compressed air is a dangerous energy source for the unsuspecting. That’s why hydrostatic testing is mandated every five years for SCBA cylinders, and high pressure composite cylinders are retired after 15 years.

Crud. I was hoping to hear from danceswithcats as he is a licensed contractor, firefighter, and a hazmat certified commercial driver. But, I was hoping he’d say ‘Well, you’ll need a reciprocating flange router and a three quarter Johnson valve, and you’ll only be able to refill it at less than half the pressure the factory did, but, it will work’

However, given your knowledge and experience, I’ll have to give up on refilling the tank.

What about emptying it completely? How buoyant would a tank of vacuum be in water?

Thanks, Doc-you gave me a good laugh with your last post. Be safe, my friend. :smiley:

I’ve also been thinking of getting the cigar-sized CO2 cannisters used in science classes everywhere. I’d like to have some props that inflate rapidly, and seemingly on their own.

I know this can be done. One of the cats in Cats used a CO2 cannister and an inflatable prosthetic to go from a thin man to the muscular and paunchy Growltiger. I know that the cannisters are cheap*. But, I also know (I spoke briefly with ScubaBen on the subject) that without proper safety precautions, the pierced cannisters become projectiles with potentially lethal force. What do I need so that I can push a hidden button and have the tips of my seemingly-normal shoes unroll to become standard oversized clown shoes? What gas would be the best for this? What would be the cheapest?
*Any cannister you have to pierce with a cracker is obviously not refillable. However, with almost no work at all, these things make a great utitlity belt, 1920’s Style Death Ray Parts, or small whiskey flasks.

I’d say that your biggest obstacle is going to be making sure that the shoes inflate only to clown size, and don’t go on filling until they burst. Any safe gas should work equally well, and I suspect that CO[sub]2[/sub] will be easiest/cheapest, or it wouldn’t be so commonly used.

An alternate idea, though, might be to fill the prosthetics with shaped foam rubber, or some similar springy, spongy material. Use one of those vaccum pumps used to efficiently pack thick blankets and the like to evacuate it, and seal it in its evacuated state. When it comes time to inflate it, you’d just need to puncture the seal, and the compressed foam will fill it back up to its proper shape.

The weight of the metal making up the cannister is probably far greater than the weight of any air it could hold. So it would be only very slightly more buoyant than the same tank filled with unpressurized air (which is what it will be full of, if you use all the helium and leave the valve open).

That wouldn’t be a problem as long as they didn’t burst too loudly. A successful clown trick can be very funny. A failed clown trick can also be very funny.

:Shoes expand, pop, and deflate:

“Y’know, this is why my wife left me.”

I meant, what if I used a compressor to remove as much gas as possible from the tank. The valve is one-way. The tank would be vacuum or close to it then, wouldn’t it?

Doc Cathode, go to a boating goods store such as West Marine, and check out the inflatable PFDs (life jackets.) SOSpenders (West has its own brand) looks a bit like a harness, but when you pull a lanyard, a C02 cartridge inflates a liner and POOF! You have a flotation device. Perhaps you can extrapolate from there to your inflatable clown shoes. Do it for your ma. Don’t forget that sweet Bozoette. :slight_smile:

Your tank might collapse is a dramatic fashion. I once saw a huge water tank that had collapsed into itself. Somebody had opened a valve to let water out but didn’t open the valve that would have let air into the top. The weight of the water drove it out, but soon the space in the tank was at less that atmospheric pressure. The outside pressure, at 15 pounds per square inch, crushed the mighty steel tank like a beer can. It was strong enough to hold thousands of gallons of water in, but not strong enough to hold ordinary air out. :smack:

That would be really cool.

I thought atmospheric pressure was 32 PSI

Nope, ~15 PSI at sea level. You might be thinking of the ~30 inch (actually 29.92) column of mercury that constituted the older measurement.

:smack: That’s what went wrong with my bathysphere!

A RaceInflate might work. This is a cyclist’s inflator that runs off of CO2 cartridges and uses a trigger to activate. They make a large-ish cannister that will inflate 2 mountainbike tires, so depending on your props, you might get full inflation