A tank question for the HS science & math teachers out there.

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Sleestak

Sleestak

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Aug 11, 2024
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What would be more net efficient?:

A single large tank or multiple smaller tanks of equal volume?

Let's exclude stop/ startup run time & other interuptions such as bleeding seperators, etc. Maybe using electrical use as an input & the net number of gun fills acquired from the tanks as the product.

Will the smaller tanks depressurize to a unusable point sooner thru use than the big tank?
 
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Not a teacher but large tank anyway. Fill a 6.8l to 300b = 2,040l of air. Say you have a gun with 580cc bottle and you top it off from 120b to 250b, meaning one “fill” from 120 to 250 requires roughly 75l. Taking out 75l of the 6.8l tank will cost you about 11b. So you can fill your gun 4 times to 250b before you can’t make it up there anymore, your 5th fill will sit at 245b. The same amount out of a 3l will cost you 25b so you can do it twice and your third fill will end up at 225b.

If you ignore bleeding and such and are going to shoot everything down to the same level it’s not going to make much of a difference though.

If your question is about energy efficiency and what not I’m too lazy to do the math but intuitively I’d say that one large is more efficient.
 
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d3vnull said:
There is no difference. Twp 50 c.f. tanks will fill the same gun the same ammount of times as a 100 c.f. tank with everything the same. The only variable in the equation is if you are filling the gun from empty the first fill.

There is a calculator for tank fills in the Calculator forum
Click to expand...
If you use smaller tanks, cascading is a way to make the most of the air (work) that you have. If you can mitigate bleed down losses and making air is inconvenient, maybe cascade 2 cylinders? The plumbing cost of a 4500 psi cascade makes it kind of a waste of time outside the commercial setting imho. I just went the lots of scbas route.
 
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I am a retired mechanical engineer. I did not do the math but I am pretty sure the same volume of air at the same pressure in two tanks will work for gun filling almost exactly the same as one larger tank. The smaller tanks will go down in pressure faster, of course, but there are two. The thought of using a tank at low pressure to start the process and using another tank at higher pressure to finish it is interesting but I don't think it will get you a lot more. You could play with the fill calculator to try different scenarios. I see no scenario where one large tank will give you more fills.
 
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Sleestak said:
What would be more net efficient?:

A single large tank or multiple smaller tanks of equal volume?

Let's exclude stop/ startup run time & other interuptions such as bleeding seperators, etc. Maybe using electrical use as an input & the net number of gun fills acquired from the tanks as the product.

Will the smaller tanks depressurize to an unusable point sooner thru use than the big tank?
Click to expand...
From a maintenance standpoint the single tank but it depends on how many and how often you are filling other bottles
 
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@6gun got it correct - if you use two smaller tanks in a cascade system that will be far more efficient than one large tank (or two tanks half the size of the large one but run independently).

It is important to know what that means though - both tanks will be connected together and to your gun. First you will open the tank with the lowest pressure and fill the lines and your gun as high as you can get it off that tank, then you close that valve and complete the fill off the tank with the highest pressure. Then (ideally) with both tanks valves closed, you will open the valve on the lower pressure tank and let the higher pressure that is in the air line "vent" back into that tank, raising the pressure slightly. This obviously saves some of the vented air, plus also results in only "venting" air out of the higher pressure tank by the amount equal to where the lower pressure tank ended up and not the full amount.

This will give you a good number of extra fills out of the same amount of available air. I could do, and then walk you through the actual math but I don't really think it is worth the effort - but cascades do save air and result in more fills.

But as 6gun also said, the cascade system of hoses and fittings will cost a good bit - maybe at least $100 or so - and if you have your own compressor that will pay for many hours of runtime in electricity. If you want to work off of fills from a dive shop though it would be a good way to go.
 
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Considering what I have learned recently not for this exact question , but it's a lot easier on a compressor to fill 10 small tanks than one large one
So I would go to for smaller vs. bigger to extend my compressor life , or maintenance. I have to fill , and stop several times to fill the large tank , and a few small ones are a lot easier to maneuver around than a large one OV.
Now for the question at hand as we all know 2 five liter , and one ten liter have the same volume of stored air , but the answer comes like this. If the 2 five liters are staggered using one first then the other there would more efficientcy in this. For example topping off a tube in an airgun from say 2000 to 3000 with the first 5L bottle untill it reaches 3,000 then switch to the second bottle which is full pressure again , and topping off untill it reaches 3,000 will actually give you more top offs than a 10L tank will as it reaches 3,000. 2 smaller tanks staggered = more better.
There will be more volume of air at less pressure in the 10 L tank when done than the 2 five liter tanks
Just try it , and see that's the only way to know for sure.
 
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Even though I have no data or even the education to work the problem out, I agree w the conclusion that realistically the smaller tanks will give more fills at the end of the experiment.

But more of as a thought experiment I was thinking in terms of direct filling from each tank until it reaches a determined low pressure & using no hacks to make it go further ...under those conditions would it be the same?
 
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Real life.

1. Charging a supply air tank to > 250 bar is a waste of time:

idf-global.com

200 or 300 bar? - International Diving Federation

Are cylinders that are filled to 300 bar a better solution than the standard 200 bar? This article will try to answer this question.
idf-global.com idf-global.com

2. For the maximum usable volume from any size supply air tank you must minimize system losses:

a. Temperature losses during supply tank charging - cool the supply tank in a refrigerator before charging, to counter compression temperature increase and subsequent pressure decrease as tank cools.

b. Maintain the volume of bleed air to fill tank volume as low as possible.

3. Two small air supply tanks fit in my refrigerator, my one large one does not.
 
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Troy Bakel said:
Real life.

1. Charging a supply air tank to > 250 bar is a waste of time:

idf-global.com

200 or 300 bar? - International Diving Federation

Are cylinders that are filled to 300 bar a better solution than the standard 200 bar? This article will try to answer this question.
idf-global.com idf-global.com

2. For the maximum usable volume from any size supply air tank you must minimize system losses:

a. Temperature losses during supply tank charging - cool the supply tank in a refrigerator before charging, to counter compression temperature increase and subsequent pressure decrease as tank cools.

b. Maintain the volume of bleed air to fill tank volume as low as possible.

3. Two small air supply tanks fit in my refrigerator, my one large one does not.
Click to expand...
Yes, the fill above about 250 bar is not linear . . . does that justify calling it a "waste of time?"

For most of us, we are not wasting much time in filling our tanks rated to 300 bar up to that level - yes, the fill time is less efficient than ideal, but we still get a lot more fills out of the added air and that is a good deal to most of us. We keep doing it, so it must be worth the trade off . . .

By your logic, since vehicles use much more fuel per mile driven at 70-80 mph than at 55-60 mph, nobody should be willing to ever drive faster than 55 or so. But clearly that does not match what we experience out there, so the trade off must be worth it to most of those drivers . . .
 
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AlanMcD said:
Yes, the fill above about 250 bar is not linear . . . does that justify calling it a "waste of time?"

For most of us, we are not wasting much time in filling our tanks rated to 300 bar up to that level - yes, the fill time is less efficient than ideal, but we still get a lot more fills out of the added air and that is a good deal to most of us. We keep doing it, so it must be worth the trade off . . .

By your logic, since vehicles use much more fuel per mile driven at 70-80 mph than at 55-60 mph, nobody should be willing to ever drive faster than 55 or so. But clearly that does not match what we experience out there, so the trade off must be worth it to most of those drivers . . .
Click to expand...
According to me ...... that would be a yes .... obviously.

Now in regards to anyone's opinion, including mine - If their status of sucking air on this planet is not relevant to you enjoying a good bowel movement, then they are irrelevant. ~ Marine Gunnery Sargeant explaining to me on who to shoot in an oversight situation.

Also applies on who is worth listening to.
 
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AlanMcD said:
@6gun got it correct - if you use two smaller tanks in a cascade system that will be far more efficient than one large tank (or two tanks half the size of the large one but run independently).

It is important to know what that means though - both tanks will be connected together and to your gun. First you will open the tank with the lowest pressure and fill the lines and your gun as high as you can get it off that tank, then you close that valve and complete the fill off the tank with the highest pressure. Then (ideally) with both tanks valves closed, you will open the valve on the lower pressure tank and let the higher pressure that is in the air line "vent" back into that tank, raising the pressure slightly. This obviously saves some of the vented air, plus also results in only "venting" air out of the higher pressure tank by the amount equal to where the lower pressure tank ended up and not the full amount.

This will give you a good number of extra fills out of the same amount of available air. I could do, and then walk you through the actual math but I don't really think it is worth the effort - but cascades do save air and result in more fills.

But as 6gun also said, the cascade system of hoses and fittings will cost a good bit - maybe at least $100 or so - and if you have your own compressor that will pay for many hours of runtime in electricity. If you want to work off of fills from a dive shop though it would be a good way to go.
Click to expand...
Thanks for elaborating on how to use it. I guess my time in the early years of hpa paintball paid off. The shop I was affiliated with used 8. 8! K sized cylinders cascaded behind 2 auto start stop dive compressors as a way to limit power use. At least the last 3 were for top off pressure and weren't utilized until they couldn't reach 4400 for customers.

Cascade is all about HOW you use them.
 
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1handwill.gc said:
One large tank would be cheaper than buying two smaller tax glass. You would need the hard work to connect them and I think it’s easier to fill out one large tank compressor and two small tanks
Click to expand...
Putting out an ad in your local area for free out of date cylinders paid off for me. I've traded labor or bought only 3 of my cylinders. I'm out 200 dollars cash money otherwise on the vast collection that many of you have seen or can see in the air cylinder thread.
 
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Troy Bakel said:
Real life.

1. Charging a supply air tank to > 250 bar is a waste of time:

idf-global.com

200 or 300 bar? - International Diving Federation

Are cylinders that are filled to 300 bar a better solution than the standard 200 bar? This article will try to answer this question.
idf-global.com idf-global.com

2. For the maximum usable volume from any size supply air tank you must minimize system losses:

a. Temperature losses during supply tank charging - cool the supply tank in a refrigerator before charging, to counter compression temperature increase and subsequent pressure decrease as tank cools.

b. Maintain the volume of bleed air to fill tank volume as low as possible.

3. Two small air supply tanks fit in my refrigerator, my one large one does not.
Click to expand...
The ideal gas law has entered the chat. 😁
 
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