Topping up da toobs

Limey Linda · 14 January 2008, 02:30

Has anyone used a CO2 for topping up the tubes. I have a few paintbal gun cylinders that I can refill from a large tank at home. Any comments would be welcome. I know you cannot do it too fast without freezing.
Thanks

keelhauled · 14 January 2008, 07:33

Often did it from dive bottle, just keep the jet about 3 inches from the valve then when the tube gets hard the pressure equalizes and valve lets no more in. The only thing about CO2 is the fact that it becomes a weak acid when disolved with any salt water that may be in the tubes, so may rot the tubes from the inside.

Limey Linda · 14 January 2008, 20:24

Quote:

Originally Posted by keelhauled

Often did it from dive bottle, just keep the jet about 3 inches from the valve then when the tube gets hard the pressure equalizes and valve lets no more in. The only thing about CO2 is the fact that it becomes a weak acid when disolved with any salt water that may be in the tubes, so may rot the tubes from the inside.

That is could to know, thanks. I assume there would no problems using nitrogen.

Tim M · 14 January 2008, 20:27

I don't see why not - afterall liferafts are filled with CO2 very quickly.

Cookee · 17 January 2008, 10:22

Quote:

Originally Posted by Limey Linda

That is could to know, thanks. I assume there would no problems using nitrogen.

I seem to remember that nitrogen is preferred as it is less likely to leak (bigger molecules or something) and expands less in heat - might be wrong though! I think they might fill tyres with it as well for a similar reason?

Nos4r2 · 17 January 2008, 10:45

Quote:

Originally Posted by Cookee

I seem to remember that nitrogen is preferred as it is less likely to leak (bigger molecules or something) and expands less in heat - might be wrong though! I think they might fill tyres with it as well for a similar reason?

Someone on Iboats.com forums suggested filling the tubes with nitrogen for exactly that reason-apparently it's common in the USA to fill tyres with it.

Quote:

Originally Posted by Tim M

I don't see why not - afterall liferafts are filled with CO2 very quickly

Not sure the comparison to liferafts really counts though-they aren't left inflated for years at a time. It's an interesting question though.

Pete7 · 17 January 2008, 12:48

Quote:

Originally Posted by Nos4r2

Someone on Iboats.com forums suggested filling the tubes with nitrogen for exactly that reason-apparently it's common in the USA to fill tyres with it.

Surely our tubes have 79% Nitrogen in them anyway?

Pete

BassBoy · 17 January 2008, 16:55

Hows about hydrogen! The positive bouyancy must reduce fuel consumption! Maybe thats what they use in them french ribs?

Seriously though........what about helium? Anyone done any experiments? Very expensive though.

Pete7 · 17 January 2008, 17:00

Helium costs about 1p per litre, now work out how many litres you would need to fill your tubes. The other problem is helium is a very light gas and would leak out past valve seals and through the material seams.

Oddly enough ordinary air seems to be quite a cost effective solution

Pete

BassBoy · 17 January 2008, 17:06

Cheaper than I thought!

My question was really...... has anyone ever tried it?.
I'm sure some crazy naval architect has had access to the required seaming/valve technology and budget to give it a go.

Poly · 17 January 2008, 20:39

Quote:

Originally Posted by BassBoy

Cheaper than I thought!

My question was really...... has anyone ever tried it?.
I'm sure some crazy naval architect has had access to the required seaming/valve technology and budget to give it a go.

Ignoring the problems of sealing. The weight difference is tiny. In a typical 6.5 m rib the tubes will (roughly) have a volume of 3000-4000 L. So at best would save you about 4 kg of weight. Thats about the same as one small spare (car sized) fuel can, or everyone on the boat going to the toilet before they leave, or probably completely drying the inside of the boat and bildge.

Limey Linda · 17 January 2008, 22:05

I did some digging around in the garage and found a 1 ltr. nitrogen tank rated to 3000psi. It has a regulator on it bringing down to 800psi, a pressure gauge and safety valve. If I can fill it to 2000psi this would seem to give a useful volume of gas at 2psi. Any math. whiz kid want to run a sanity check on this?

Limey Linda · 17 January 2008, 22:11

I did some digging around in the garage and found a 1 ltr. nitrogen tank rated to 3000psi. It has a regulator on it bringing down to 800psi, a pressure gauge and safety valve. If I can fill it to 2000psi this would seem to give a useful volume of gas at 2psi. Any math. whiz kid want to run a sanity check on this?

v666 · 17 January 2008, 22:39

Could well be wrong here, but i think at atmospheric pressure (14.7 PSI) you would get 130L (ish) from the full tank. (you get 660L from a 5L oxygen tank)

Not sure what you would get at 2psi - 1000 ish

Tim

Pete7 · 17 January 2008, 23:15

Quote:

Originally Posted by Limey Linda

want to run a sanity check on this?

I think you will need about 30 of them to pump your tubes up from flat.

Pete

Poly · 17 January 2008, 23:43

Quote:

Originally Posted by Pete7

I think you will need about 30 of them to pump your tubes up from flat.

Pete

I got 20 of them but it obviously depends what assumptions you make about limey's tubes. (I was assuming 50cm diam and total 15m long).

Limey Linda · 18 January 2008, 00:13

Quote:

Originally Posted by Polwart

I got 20 of them but it obviously depends what assumptions you make about limey's tubes. (I was assuming 50cm diam and total 15m long).

That's about right and as already stated I only intend to use nitrogen tank to top off rather than carry a 12v. pump. I carry a stirup type pump also but the ally tank would be a lot easier. Just found out I can fill the tank for about 2 bucks at the paintball range at the end of my road.

Thanks for the input. BTW, if the tubes are totally flat I use my big arse compressor to fill them. Just a tip if using a compressor you need to make an expansion chamber in the fill tube as high pressure air will damage the tube valve and do not use a fixed attachment just a push fit so you have to hold it in place. Otherwise a small distraction could end up with burst tubes.

Pete7 · 18 January 2008, 09:27

Quote:

Originally Posted by Polwart

I got 20 of them but it obviously depends what assumptions you make about limey's tubes. (I was assuming 50cm diam and total 15m long).

Yep plus I added the pressure to raise above atmospheric and a fudge factor because there will be some leakage changing over cylinders.

Still think a foot pump is a better solution, its free with unlimited supply of gas and good exercise which some of those colonists could do with

Pete