Low cost Carbon Fiber tank option

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texagdds

texagdds

Member
Feb 27, 2018
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Tx, United States
First I would like to thank Centercut for his invaluable info on this - if you like it enough to +1 me, think about giving him some love too. If you are getting into this and will be getting a compressor, you’ve noticed the carbon fiber tanks are pretty expensive. You can find low cost used military use Carleton tanks on eBay that are high quality and low cycle, you just need to know what to get to make them work with pcp’s.

Here are examples of what’s needed. 

Tank:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F302604949586

Valve Replacement:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F291256856001

PCP Fill Rig:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F302662847047

Oncw you get thentank you will have to remove the Carleton style valve (making sure it is empty of air first). I found this video helpful. Instead of the custom pipe with thread I used a large pipe welrench and a hammer to break the seal and remove. Took less than 2 min. 

Valve Removal:
https://youtu.be/k5LgJ-vuDeA

You might need a new Valve neck O-Ring to install on your new/used valve if it doesn’t come with one such as the one in the link below (make sure you measure to see if it is the correct size)

https://www.amazon.com/dp/B00P4CNX7G/ref=cm_sw_r_sms_c_api_zmlZAb2ZRKWGY

Once finished you you have a carbon fiber tank suitable for many fills for your pcp, refillable from your own compressor for less than 150$. 

Here is what mine looks like all put together. 

1523364904_11345078605accb42880fb72.53890123_ED88C0EA-A17D-46A7-80C2-B01F56E6E8D9.jpeg


You most likely won’t be able to get them hydro tested because they will most likely be out of date, but there are many threads dealing with their safety - and you’ll have to be the judge of whether you feel safe using them or not. Hope this helps. 
 
Although this sounds like a great idea, I would strongly recommend having tanks hydro-tested even if you are filling your own tanks. The cost is not that much compared to a hospital bill. When looking at these tanks, be sure to check the dates and I would try to make sure they have at least 5 years of life left. I am certain that the safety factor on these tanks are high and I probably would go a few years past the expiration date but understand there is a risk and the cost could be great.

I remember well, the high cost to enter the PCP world and like you, I looked at every aspect to keep the cost down. In the end I went with a new tank for safety reasons. I really don't think it is a good idea to buy out dated tanks. In the US, the life of a tank is 15 years. I am certain tanks can go longer..........but for how long. Eventually they will fail. This could be just a leak or an explosion. You won't know till it happens!

As I stated before, when purchasing a used tank, make sure there is some "life" in the tank and be sure to have it inspected (hydro-tested). Then, you are sure you have a safe tank!

NMshooter
 
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Right. These can actually be hydro tested- but you have to be sure the company knows what’s going on and that these are extended life tanks - otherwise you get a hole drilled in them. You can also get them hydro tested without a recertification. 

One thing to remember about the safety ratings of these tanks - the primary reason they were invented was to keep someone alive under water, therefore they have to be extremely reliable, hence all the regulations. The service life of a “dry” scuba tank should be longer, because the duty cycle is less. Likewise these Carleton tanks have a longer life span than the normal tank you would get to fill up a pcp. 

Again- if you don’t feel or think it is safe, you shouldn’t do it. I get it - the thing is a bomb with air. 
 
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​Just an opine, not a rant - I know we won’t change anything here. Just food for thought. 

Hydro testing takes the tank to 7500 psi? Holy crap! Seems like there could be a better way of evaluating the tank other than taking it to its failure limits. Seems like the testing in and of itself decreases the life span of a tank. Think of the flexure that happens - kind of like work hardening (Bend a paper clip back and forth it eventually breaks). I mean- I can test an engine for its limits on a dyno, but each time I do it I risk killing the engine because the parts can fail at extremes. Much like Ultrasound or radiographic testing of welds, could you evaluate for stress fractures/weak points using less destructive methods? 

 
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Not to worry. The test pressure is 5/3 times the design service pressure. The cylinder must have a minimum safety factor (burst/service-pressure ratio) of 3.4. So although the tank is hydro’d at 7500 psi for one minute, the minimum burst pressure is 15,300 psi. When manufacturing, one tank per lot is taken to this pressure, and then pressure is increased until it fails. Also, one tank per lot is cycled to 7500 psi a minimum of 10,000 times. 
So, one cycle once every 5 years to 7500 psi for one minute does not adversely affect the tank. 
 
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I will say this about high pressure tanks.  I am a coward. This thing is holding 4500 PSI of air. Yes, the regulations are really strict. Yes, is some ways, the regs are so strict and conservative, they seem stupid. They were, after all, designed for scuba divers, not Paintball tanks.

Then again, if one fails and becomes a projectile, or if one just explodes (probably one in a couple million), how many people might it hurt? How long does it take them to heal? If it was my tank, I'd feel mighty bad knowing that I hadn't done everything possible to protect the people around me just to save a couple bucks. Then of course, the legal hassles would be endless for years to come!

Design and max specs are there for a reason. Even if I filled my own tanks, I'd still have them tested on time. It's only $40 every 5 years, and a new tank is only $260 for a new tank with regulator, or about $160 without a regulator if you have the reg off the old tank.

Those who have done risk analysis would recognize that this is in the Low probability of occurrence, but HIGH Impact if it does occur quadrant of the 4 square chart.

We each have to make our own risk decisions, but walking around with something that could explode with the power of a stick of dynamite should cause a bit of care and respect!

 
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I believe in being safe, but if you are getting into pcp's you have to know there is some risk, otherwise I would have been content with my multi pump air rifles.

When the standards for carbon fiber tanks was set there was no vision of us airgunners using these to fill pcp guns with them. The standards were designed for people using tanks in much more hostile environments such as a firefighter or scuba diver. The thought was these people have these tanks strapped to their backs in harsh environments so standards were set accordingly.

Those who want to abide by those standards if it makes them feel safer that's ok, I have decided not to. Thus far I haven't seen, heard, or read about an airgunner having a carbon fiber tank explode. I hear plenty about the risk of this happening, but haven't come across it. 

I have come to believe there is a lot fear mongering going on around this sport with the intended purpose of selling us over priced products, some probably imported from the same place we are warned about. I suppose if I was selling air tanks, fittings, etc. I might tend to hammer home the importance of safety and why you should throw that tank away after it expires and buy a brand new safe one from me. 
 
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Yup, I understand that the rules were set for industries other than air rifles, and the ability to build a better tank is always getting better, but I worked in mining and natural gas for too long. Safety, Safety, Safety. They drilled safety into us 'cause people got killed on the job, and yes, I was working at one company when someone got killed. Didn't follow procedures and didn't blow down a high pressure line properly. It doesn't happen often, and may never happen, then again, , , , , , 

Same goes for airguns. I don't know of anyone being injured or killed from tanks rupturing, doesn't mean it hasn't happened or won't.
 
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I'm with Centercut....elsewhere is listed the Carlton, Scott etc dot tank #s that qualify for a 30year life....I bought two different tanks one actually is good till June....both are on the qualifying 30years list....both have pressure relief burst disc safeties on the valves...

Unless there are obvious cut fiber or crush evidence or burns I trust these American tanks....if you research the information, inspection manual and testing procedures for these tanks, you will find the safety factor surcharge designed in way overkill....

Yes we should be safe....but I can't imagine a scenario with me doing anything to these quality tanks to burst one ....short of a fire or a bullet.
 
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My understanding is that paintball tanks (actually used in competition) fail hydro from time to time because they get beat up so much and shot down to lower pressures, so the aluminum tank expands and contracts quite a bit. Airgun tanks don't usually fail because we lavish TLC on the equipment and rarely let the pressure fall below our shooting pressures. That means expansion and contraction under pressure is much more limited. Aluminum does get brittle when fatigued. Any tank subject to hard knocks like fire departments other high stress situations more likely to fail.


​good stuff at 2:10 into the video. Of course, their credibility will be questioned. After all, they just want to sell services and equipment.

​Of course, an example of the power of the tanks is here:

​Good footage is at 2:23. Slow motion follows.

​
 
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I kinda doubt anyone will hydro the tank. It's now 15 years old, and just by age, I believe it will be condemned unless you send it to whatever place it is that completely recertifies the tank for around $300. If that's not the case, please let me know. I just had my tank hydro'd and the first question was if it was over 15 years old or not. When you call the local hydro tester, ask about the "Born On" date and if they hydro anything over 15 years old. If not, it may come back with a hole drilled or at least marked "Condemned" due to age even though it's a solid tank.

​Rocky Mountain Air, a division of US Welding did my tank last week. $36 by the time it was all over including tax.

To legally extend the life of the tank, look up Digital Wave Corporation. They do an Ultrasonic evaluation of the tank, under special permit.
https://www.digitalwavecorp.com/
https://www.phmsa.dot.gov/news/phmsas-new-cylinder-special-permit-maintains-safety-standards-while-offering-cost-savings-first

​My understanding is that it's about $300 per tank, so it ain't cheap. In my case a new tank with reg is only $270. In your case, with a larger tank, it might be worth it.
 
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