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Author Topic: Nitrogen.  (Read 3586 times)

ncrary

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Re: Nitrogen.
« Reply #15 on: May 20, 2017, 12:37:19 PM »
I am looking into this.  My local welding supply quoted me $10 month rental, $200 to buy outright and $130 for refills.  Price looks good.  However, I am not a mathematician and no matter how many times I add, divide, or multiply, the numbers do not make sense.  How many times can I fill a 88 cubic foot bottle from 3000 psi to 4500 psi from a 6000 psi 335 cubic foot nitrogen tank?
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Alan

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Re: Nitrogen.
« Reply #16 on: May 20, 2017, 03:44:00 PM »
The way you shoot, you'll need to refill the beast about once a month! Geez, I thought I shot a lot of lead!
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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

Christopher

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Re: Nitrogen.
« Reply #17 on: May 21, 2017, 06:25:22 AM »
ncrary said
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How many times can I fill a 88 cubic foot bottle from 3000 psi to 4500 psi from a 6000 psi 335 cubic foot nitrogen tank?


The best I could figure  ??? (and believe me it was a struggle) it would be about 3.5 refills, but that doesn't take into consideration van der Waal's effect. Which basically says that at higher pressures your not really putting as much air in your tank (on a molecular level) as what your gauge is reading. I would imagine that it would have a more noticeable impact on the pressure drop from 6k-->4k than from 4.5k -->4k -->3.5k and so on....Trying to compute that (van der Waal's effect) into the equation is outside of my capabilities. 

Hopefully Bob will give us his input.

Hope that helps,
Chris
« Last Edit: May 21, 2017, 06:31:00 AM by Christopher »
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ncrary

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Re: Nitrogen.
« Reply #18 on: May 21, 2017, 06:09:53 PM »
Using the P1V1 = P2V2 relationship I come up with about 5 fills.  Mu guts tell me that is not the case, since I will not be filling from 0 to 4500 psi, but from about 3000 to 4500 psi.  My math skills have failed me.  I should have paid more attention back in 1964.

Help, Bob.
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Christopher

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Re: Nitrogen.
« Reply #19 on: May 22, 2017, 02:43:34 AM »
Well, I had a time trying to find what the actual liquid capacity was on the 335 cu ft tank. I really only found one source online and it says that it has a liquid capacity of 50 liters http://www.cylsonic.com/cylsonic/Products/Understanding-UE/Cylinder-TypesSizes.htm ......Then Lloyd Sikes fill calculator states that an 88 cu ft tank has a capacity of 1442 cc's http://www.calc.sikes.us/2/...If your big tank has a fill of 6k and you will be taking it down to 4.5k that is the difference of 1.5k....on your 88cu ft tank you are going from 4.5k down to 3k, again a difference of 1.5k.....So if both are being drained 1.5k psi or 103.4bar, the ratio of fills will be determined by size......Thus the big tank is 50 liters (assuming the numbers from the above website are correct) 50 liters=5000cc and the smaller tank is 1442cc then it would be 5000/1442=3.46 fills

Chris

Edit: Modified to strike out wrong calculations, I came close to the right answer, but it was simply coincidence :-[
« Last Edit: May 23, 2017, 02:29:44 AM by Christopher »
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ncrary

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Re: Nitrogen.
« Reply #20 on: May 22, 2017, 07:12:07 AM »
Those numbers don't seem realistic somehow.  I would expect to be able to fill many more times than that.  Maybe my gut is wrong, and if it is, then nitrogen is definitely not the way to go.
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jhm757

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Re: Nitrogen.
« Reply #21 on: May 22, 2017, 08:53:15 AM »
My 6000psi Nitrogen tank costs me $100 a year to lease the tank, and $60 for a refill.

A tank lasts me for a year, and that is a lot of shooting, so total cost is $160 a year.

Only draw back is once it is under 4500psi you don't get a full fill on the 4500psi carbon fiber tank. but still lots of shooting left.

But it sure is nice to always have Nitrogen, and only have to refill once a year. I keep the tank strapped to a beam in the garage.

It is very heavy when it is time to take it in for an exchange. I imagine I could have the exchange delivered, need to look into what they charge for that.

Jim - jhm757

Christopher

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Re: Nitrogen.
« Reply #22 on: May 22, 2017, 12:34:12 PM »
ncrary said
Quote
Those numbers don't seem realistic somehow.  I would expect to be able to fill many more times than that.

It does seem off somehow, I would have thought it would have been much more as well. I'll definitely be the first to say that I could be wrong, as I admitted earlier it was a challenge to try to figure it out and math isn't my strong point either, but now I'm really curious.  I'll post a link for this over on the Ask Bob forum and we'll call in reinforcements 8) he'll get to the right answer I'm sure.

Chris
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ncrary

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Re: Nitrogen.
« Reply #23 on: May 22, 2017, 01:26:12 PM »
My 6000psi Nitrogen tank costs me $100 a year to lease the tank, and $60 for a refill.

A tank lasts me for a year, and that is a lot of shooting, so total cost is $160 a year.

Only draw back is once it is under 4500psi you don't get a full fill on the 4500psi carbon fiber tank. but still lots of shooting left.

But it sure is nice to always have Nitrogen, and only have to refill once a year. I keep the tank strapped to a beam in the garage.

It is very heavy when it is time to take it in for an exchange. I imagine I could have the exchange delivered, need to look into what they charge for that.

Jim - jhm757

Jim,

That doesn't tell me how long it will last for me.  I need a hard number of refills you can get.  If you refill your 4500 psi tank once a month and I refill once a week, or maybe twice when I am out squirreling, then the nitrogen tank will not last as long for me.  So, with $130 refills here, I need to know how many times a year I would be refilling.  If the cost warrants it, I will get a compressor.
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rsterne

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Re: Nitrogen.
« Reply #24 on: May 22, 2017, 02:55:59 PM »
Here is my answer to the PM I received on this, as I figured others would be interested....

The internal volume of an 88 CF SCBA tank is 550 CI, it holds 88 CF at 4500 psi.... The standard 6000 psi steel cylinder is a DOT 3AA-6000, and they have an internal (water) volume of 1.50 CF.... and are typically listed as 480 CF (sometimes called a 510 CF).... 6000 psi is 414 bar, so using Boyles, that should be (414 x 2383) / 1728 = 570 CF.... Using VanDerWaals for Nitrogen instead of using 414 bar, we use a factor of 322 (339 for air), so at 6000 psi it should contain (322 x 1.50) = 483 CF (509 CF for air).... so that 480 (510) CF is pretty close.... If your Nitrogen tank is a different size, or not filled to 6000 psi, then the calculations below are wrong....

The problem is, that both tanks contain fewer CF of air (or Nitrogen) between your fill and refill pressure than a linear relationship would suggest, due to the VanDerWaals effect.... The only real way to do this is to use the density of Nitrogen at the three pressures (6000, 4500, and 3000)....

Density of Nitrogen at 6000 psi = 376.1 kg/m^3
at 4500 psi = 310.1 kg/m^3
at 3000 psi = 225.1 kg/m^3

From that, we can calculate the weight of Nitrogen released from the large tank (assuming 1.5 CF internal volume)....

1.50 is 0.0425 m^3.... so at 6000 psi it contains (376.1 x 0.0425) = 15.98 kg. of Nitrogen.... and at 4500 psi, (310.1 x 0.0425) = 13.18 kg.... The difference is (15.98-13.18) = 2.80 kg. of Nitrogen released for a drop from 6000 to 4500 psi....

550 CI is 0.00901 m^3.... so at 4500 psi the SCBA tank holds (310.1 x 0.00901) = 2.79 kg. of Nitrogen.... and at 3000 psi, (225.1 x 0.00901) = 2.03 kg.... The difference is (2.79-2.03) = 0.76 kg. of Nitrogen required to fill it from 3000 psi back to 4500....

The number of fills is the weight of Nitrogen released from the big tank, divided by the weight of Nitrogen required to fill the SCBA tank.... (2.80 / 0.76) = 3.68 fills....
Kudos to you for coming up with 3.5 fills....  8)


Bob
« Last Edit: May 22, 2017, 03:32:36 PM by rsterne »
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ncrary

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Re: Nitrogen.
« Reply #25 on: May 22, 2017, 04:37:13 PM »
Thank you, Bob.

So, assuming I need to fill my bottle once a month on average for the year (so far I am filling it about once every two weeks on average this year), I would need to fill the N2 tank 3-4 times a year at $130 per fill, and rental is $10 a month, that puts me at $510 - $640 a year for nitrogen, with the dive shop charging $10 for a fill, that is about $250 - $400 per year.  My local gun shop is building a new store with an indoor range with shooting lanes at 25, 50, and 100 yards, indoors!  So my shooting in the winter will be much more than in the past.  I am 70 now, if I stay healthy and shoot another 10 years, that could be between $2500 to $6400 for air/nitrogen.

A $1300 - $2000 compressor is looking better all the time.
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Alan

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Re: Nitrogen.
« Reply #26 on: May 22, 2017, 04:50:24 PM »
You are a youngster! I've got you by 7 years, and I opted for the Omega Air Charger. It is exactly what you need (I didn't know I needed it until I got it!). And, the next scheduled maintenance for the gearbox is 3,500 hours. Me thinks it will outlast me!

« Last Edit: May 23, 2017, 04:19:04 AM by Alan »
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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

Monkeydad1969

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Re: Nitrogen.
« Reply #27 on: May 22, 2017, 10:17:57 PM »
There's some good info here.  Thanks for all the input.

Joe
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Christopher

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Re: Nitrogen.
« Reply #28 on: May 23, 2017, 02:35:50 AM »
Thanks Bob for the response, as always.......I appreciate the kudos, but it was dumb luck, as you probably saw. Edited my post to strike out wrong capacities....which was all of it. ::) :-[

Chris

 

 
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rsterne

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Re: Nitrogen.
« Reply #29 on: May 23, 2017, 07:36:39 AM »
The information I have found is that the CGA-580 fitting used on 3000 psi Nitrogen (and inert gasses like Helium and Argon) is not used on the higher pressure tanks.... The fitting for 6000 psi Nitrogen tanks is shown as a CGA-677 in the list below....

http://www.sisweb.com/referenc/tools/cgafitt.htm

The CGA-580 Nut is 15/16"-14 RH male threads.... while the CGA-677 Nut is 1.03"-14 LH female threads....

Bob
« Last Edit: May 23, 2017, 07:38:45 AM by rsterne »
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