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 Post subject: Problems refilling after topping off bottles
PostPosted: Wed May 03, 2017 9:10 pm 
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I've been using air to top up the pressure in my 2.5lb bottles, which works wonderfully, but now when i try and refill it by decanting from my 10lb bottle, the pressure is still so good it pushes the nitrous back into the big one. It took a lot of heating to get the big bottle to put any back in and getting it full is becoming more and more tricky.
I've tried tipping the bottle upside down and opening the valve to loose the air but it doesn't work, it just looses the nitrous (or at least i think it does as the weight drops dramatically) but the pressure hardly changes.

Any thoughts or suggestions?
Cheers
Phil


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 Post subject: Re: Problems refilling after topping off bottles
PostPosted: Wed May 03, 2017 9:48 pm 
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How are you filling them with air and to what purpose? By adding air to a nitrous cylinder, you're displacing the space where the nitrous is supposed to go. The best method to obtaining the correct flow rates are A) increase the bottle temperature to the appropriate level or B) increase the nitrous flow by using a larger jet. The fact that the bottle won't fill is due to the lack of pressure differential.

The easiest way to both fill and top off a nitrous bottle is too have a great pressure differential. This could require heating up the mother bottle enough, and in some cases, cool the receiver bottle.


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 Post subject: Re: Problems refilling after topping off bottles
PostPosted: Wed May 03, 2017 10:08 pm 
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Hi, thanks for your reply.
After refilling the bottle with nitrous to it's usual full weight, I'm then adding high pressure compressed air to take the cold bottle pressure from 750psi to 900psi, this saves me the performance of heating it to achieve the same result and the hassle of keeping it warm whilst waiting to run.

Heating doesn't work very well as the pressure drops almost immediately during a run and the bike runs richer and richer as the pressure drops. By using air it still drops but nowhere near as significantly.


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 Post subject: Re: Problems refilling after topping off bottles
PostPosted: Wed May 03, 2017 10:18 pm 
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All is well with clever ideas, but as you found out it means depleting the bottles completely in order to service them properly to full and that can be wasteful and costly. You may want to try adding multiple bottles to your setup so that the pressure does not drop during the run and top offs will be much more efficient.

Nitrogen push systems work pretty well too, but they have some disadvantages as well. The most balanced setup is using a larger nitrous supply. You could use a larger nitrous cylinder, but using multiple smaller cylinders gives the liquid nitrous more surface area to stay heated when in use.

The bike simply shows symptoms of running too small a nitrous reservoir.


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 Post subject: Re: Problems refilling after topping off bottles
PostPosted: Wed May 03, 2017 10:31 pm 
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Thanks again, that was the answer i was hoping not to get lol. It does work very well but refilling becomes hard and i still have nearly 1.5lb in a 2.5lb bottle after each run so i don't want to waste all that.
I'm not keen on adding more bottles or more anything to the bike as it's just more weight on an otherwise very light machine.

what i've been contemplating is actually emptying as much as possible after a run from the 2.5lb cylinder back into the big 10lb one, this should be fairly easy as it's pressure is now higher anyway. Then, when it's nearly all transferred just waste the last bit to get it completely empty, and then start again. It will end up with the big cylinder having quite a high pressure but that gets emptied eventually anyway so i can relieve the pressure when it's spent before having it refilled?

Would there be any drawbacks from doing this? also, i presume it will end up with water in the bottles from using air? and would the air and water add much to the weight?

Cheers


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 Post subject: Re: Problems refilling after topping off bottles
PostPosted: Wed May 03, 2017 11:00 pm 
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bikerphil wrote:
Thanks again, that was the answer i was hoping not to get lol. It does work very well but refilling becomes hard and i still have nearly 1.5lb in a 2.5lb bottle after each run so i don't want to waste all that.
I'm not keen on adding more bottles or more anything to the bike as it's just more weight on an otherwise very light machine.
The bike can be light, but if it's not making the power then it might as well weigh 5,000 kg.


what i've been contemplating is actually emptying as much as possible after a run from the 2.5lb cylinder back into the big 10lb one, this should be fairly easy as it's pressure is now higher anyway. Then, when it's nearly all transferred just waste the last bit to get it completely empty, and then start again. It will end up with the big cylinder having quite a high pressure but that gets emptied eventually anyway so i can relieve the pressure when it's spent before having it refilled?
Sounds like more work in the long run to me, but it's not uncommon to empty small bottles into the big ones.


Would there be any drawbacks from doing this?
The extra effort involved and higher chance of error. In my experience, the more times people touch things the more likely something will go wrong and cost you the race.
also, i presume it will end up with water in the bottles from using air?
Oh yes that is a high possibility and almost guaranteed.

and would the air and water add much to the weight?
It's not the weight, but the potential of water being drawn into the system and creating inconsistencies during the run.
The only thing I can say is try your method, and if it works for you then that should be enough. To me, I'd simply run a larger or multiple bottles and if need be, increase the power to compensate for the weight difference.



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