88 cu ft Tank and the amount of fills I should get with my Crown

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stoti

stoti

Member
Apr 6, 2018
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Beautiful, Conservative, Potter Valley, Nor Cal.
Hello,

I have one quick question... I bought a 88cu ft carbon tank, rated at 4500psi a while back and the tank only has one gauge on it, the gauge that measures the pressure of the air going into the gun. I can't actually see how much compressed air remains in my 88 cu. ft. tank. How many fills should I be able to get, filling up my Crown's 480 cu. cm. tank, going from 140bar to 245bar? Just want a rough estimate. 10 fills, 20, 30? My guess would be around 18-20 is that close? That guess was simply by looking at the two tank sizes and then figuring I'm not filling from 0 psi. A total guess. Thank you. Stoti

So, I posted the above question and then started thinking about how to calculate the question I asked and come up with an answer for myself. I'm baffled. I have no idea how to figure this out mathematically. Obviously, you have to take into account the size difference of the two tanks, the pressure differences, take into account your filling only from 140bar to 245bar, switch from bar to psi and probably lots and lots of other things. I'm a pretty smart guy but math was never something I liked or was motivated to explore. If somebody knows how to calculate this, I'd love to hear it. I'd also just like to know the amount of fills I should get. Someone who has filled their tank and knows about how many fills should be able to give me a close estimate. I've got about 13 fills so far. Below is some info you will need to help with the calculations. Again, thank you. Stoti

480 cubic centimeters equates to .017 cubic feet

140 bar equals 2030 psi

245 bar equals 3553 psi
 
Can’t help with the number of fills but did you know about a device called a “deadhead”? I think that’s what it’s called. It plugs into your fill hose and is solid metal. Once plugged in you open the valve on your tank like you are filling your gun. The deadhead stops the air flow and your gauge will then tell you how much pressure remains in the tank. I got mine from Joe at airtanksforsale.com You do waste a little bit of air but at least you know how much you have in your tank.
 
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Thanks adb1228. According to their calculator, I should get about 18 fills. My complete guess was pretty darn close. Thank you too Kgphotos for the info on the deadhead. Anybody else... I'd still love to hear how to calculate all of this and come up with 18 fills. That';s the number I got entering the parameters on AofA's fill calculator. Stoti
 
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Plugging in the parameters that you set out above into the AoA's calculator, it comes back as 10.6 fills. I think they overestimate on that as well, as least from my experience of using the 100 CU/FT tank. I'm lucky to get 8 or 9 complete (to 250 bar) fills on my Crown using that, but then the dive shop is only able to push their compressor to fill it to about 4400 PSI. 
 
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Yeah, I just punched in the numbers and it shows 10.5 fills. I don't know where I messed up the first time. I 'm already at 13 fills though going from around 140bar to 245bar. I keep a little log book so I know the amount of fills and the beginning and ending pressures are accurate to within about 5 bar. I guess I'm about ready to get it refilled! When I bought the tank, I thought I'd get a lot more fills than that though. I'm hoping the AofA calculator is off a bit. I also have a 80cu ft 3000psi scuba tank. Does anybody know how much cascading will help? I guess I need to give that a try. If I go from 2030psi to around 2800psi and then top it off with the carbon tank should help a lot. I'll punch in the numbers and see what that shows...

So,just checked the AofA calculator and it shows if I use my scuba tank to fill the gun to 2800psi and then top it off with the carbon tank to 3553psi, the calculator shows I'll get 21.3 fills out of the carbon tank. I didn't know it would help that much, that's more than double the amount of fills I get now. I need to start using my scuba tank too I guess, it's just sitting right there next to all of my other PCP filling equipment. Thank you guys for the info. opened my eyes I guess. I also asked the question just in time, going to need more air asap and it's good to know to take the scuba tank too. I just love Airgun Nation, what a wealth of information. Thanks, Stoti
 
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In the UK it's Liters with air but the math is very simple.

So 88 CUFT= 3.1L 300 bar is 4500 PSI etc. etc.

3.1L X 300BAR=930L-140BAR X 3.1L=434 (930-434)=496L USEABLE AIR (tank full volume minus the pressure when you get it refilled)

480CC X 245BAR=117L-480CC X 145BAR=70L, 117-70=47L per fill so you should get 10.5 fills (not including losses).

The fact that you are getting more means either the dive shop is filling the bottle to over 300 or you have an incorrect gauge (probably the gun). FX gauges have been reported to be upto 50 bar out on some occasions, 10-20 is probably much more common.

Hope that makes at least some sense!
 
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In the UK it's Liters with air but the math is very simple.

So 88 CUFT= 3.1L 300 bar is 4500 PSI etc. etc.

3.1L X 300BAR=930L-140BAR X 3.1L=434 (930-434)=496L USEABLE AIR (tank full volume minus the pressure when you get it refilled)

480CC X 245BAR=117L-480CC X 145BAR=70L, 117-70=47L per fill so you should get 10.5 fills (not including losses).

The fact that you are getting more means either the dive shop is filling the bottle to over 300 or you have an incorrect gauge (probably the gun). FX gauges have been reported to be upto 50 bar out on some occasions, 10-20 is probably much more common.

Hope that makes at least some sense!
Click to expand...

Sorry Spray1Mark, but your equation doesn't make any sense. 88 CUFT= 2492 litres. The Imperial volume in cubic feet is the pressurised capacity of the bottle and depends on what pressure the tank is rated for. The litre capacity is the amount of liquid that the tank can hold. A 9 litre tank at 300 bar or 4300 psi has a pressurized capacity of roughly 88 cubic feet.
 
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We don't work in CU FT here so it really means nothing to me sorry.

I used an online calculator to convert CUFT to L, which it tells me is 3.1L (unless it's wrong) in which case you just re-plug in the numbers changing 3.1 to 9.

The principle is simple, at 300 bar the capacity of the bottle (air) is simply 300 times what it is at 1 bar.
 
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