Pressure required to inflate latex balloon?

[Neil Baker]

Hi,

I'm sure the pressure required to fill a balloon of a specific size varies from balloon to balloon, but I was wondering roughly how much pressure was required?

Is there a website page or PDF that lists the minimum pressure required to fill a balloon based on size or type?

I may be able to obtain some free helium after it has been used for another purpose (it evaporates from a liquid to a gas to cool equipment), but the pressure I would receive it at is very low (higher than atmospheric, but possibly not much higher).  If the latex balloons require a reasonable amount of pressure to be filled, this source of helium may not be of any use.

I know the latex balloons aren't like normal party balloons (as in they have to stretch immediately and require a fair amount of pressure to get going), but am I right in thinking that although they aren't like zero pressure balloons that you can feed them with next to no pressure, they don't require that much more pressure?

Thanks

Neil.

[Steve Aerospace]

There is very little differential pressure between the inside and outside of the balloon at launch - in fact some of the larger balloons are launched in a zero pressure state - i.e. the envelope is not inflated to the point where the latex is stretching at all. The smaller balloons tend to need to be inflated past the point where the latex is starting to stretch before they will pick up their own weight and that of a payload. Even at burst the pressure is typically less than 1KPa (0.15PSI) from what I can work out.

You will need some pressure to get the gas in to lift the weight of the latex. Happy to lend you an old 300g balloon if you want to give it a go. I'd be interested in hearing the results.

Steve

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Steve Randall
Random Engineering Ltd
st...@randomaerospace.com
+44 7802 242135

[stea...@gmail.com]

However, do remember your gas law, you will not have much helium if it's at very low pressure.  You'll need between 100 to 300 cubic feet to fill typical weather balloons.  300 cubic feet squeezed into a T cylinder results in 2,800 PSI (18,000 kPa)

Thanks,

Dan

Sent from my iPhone

[Neil Baker]

Thanks Steve & Dan,

It sounds like there is a really possibility of it working.  Certainly for larger balloons.  

Thanks Steve for your kind offer of an old balloon.  If it works, I'm sure there are many businesses around Cambridge and the UK with a free supply of used helium that we may all be able to use for this purpose.

My next step is to get official permission from the business concerned.  The staff are very interested, but there are a bit worried about issues such as:

• Health and safety filling a large balloon indoors (although very low pressure and if it bursts it'll slowly deflate i guess rather than pop).
• Not wanting to be associated with the launch in case it brings a plane down (NOTAM and permission to launch from Cambridge airport will greatly reduce the change of this happening)
• Etc

Although I've not launched my own balloon yet, I've helped out many times and have read the wiki, so hopefully I'll know the answers to most of the questions they are likely to throw at me.

Thanks again for all your help and hopefully the results of this low pressure filling will be of use to someone else out there.  I guess, even if they aren't happy for me to launch, would it still be useful if I were to try and fill the balloon indoors, measure the lift and deflate it?

Neil

[stea...@gmail.com]

If you can't launch there, then it's probably not going to be worth the trouble of inflating the balloon indoors and trying to get it to a launch site.  

I suspect you'd be better off just using a consumer air compressor to compress it for storage into consumer air tanks to a few thousand kPa. (hundred or two psi)

Thanks,

Dan

Sent from my iPhone

[Neil Baker]

I wonder how much a compressor would cost to buy or rent, that could do that?  The cost may be a lot more than it would be to just buy new helium.

I guess I'd need to buy / rend a cylinder to store it in as well?