AEA Pressure limits for aluminum tanks? (AEA/BinTac airguns)

[AGN1023]

I'm considering AEA aka BinTac airguns with the 250cc aluminum tanks (e.g. S45 single tank version) but I'm concerned about running 4,500 PSI (website typo?) in a metal tank. As you know, carbon fiber is rated for 4,500 PSI but aluminum is limited to 3,000 PSI, generically.

Can some aluminum tanks compensate with greater wall thickness or alloys? I like the streamlined look & size of aluminum vs. CF bottles on those guns. Not seeking maximum shot capacity, just compactness and quicker fills.

Another aspect is that CF tanks are said to be more fragile in terms of outside pressure, e.g. the Titanic sub implosion (they say CF handles far more pressure inside). I want a tank with less risk if something hits it accidentally.

Thanks for any details.

 

[Stubbers]

Manufacturer specs are okay to fill to. You can do your own calculations with Barlow's formula, but their engineering team should have already done that as well as had them pressure tested to 3~x their stated fill pressure.

Barlow's formula is quite basic. Safety Factor commonly used for UTS = 3-3.5, for Yield 2.5.

Working Pressure = 2*UltimateTensileStrength*WallThickness/(PressureTubeOuterDiameter*SafetyFactor)

-Matt

 

[Gerry52]

Your concerns about "outside pressure" are unwarranted. Carbon Fiber tanks are extremely strong & robust. There are videos out there somewhere of guys shooting them & couldn't get the bullets to penetrate. I don't think there's anything you could do in the normal course of airgunning that would get them to fail.

 

[AGN1023]

Manufacturer specs are okay to fill to. You can do your own calculations with Barlow's formula, but their engineering team should have already done that as well as had them pressure tested to 3~x their stated fill pressure.

Barlow's formula is quite basic. Safety Factor commonly used for UTS = 3-3.5, for Yield 2.5.

Working Pressure = 2*UltimateTensileStrength*WallThickness/(PressureTubeOuterDiameter*SafetyFactor)

-Matt

Well, if I had wall thickness data (and more engineering knowledge) I could use that formula, but I'd have to cut a tank open unless they publish it somewhere.

I have some wariness of Chinese products, like tainted foods and EV battery fires due to weak regulations. Are airgun tanks required to pass official specs when imported into America?

 

[AGN1023]

Your concerns about "outside pressure" are unwarranted. Carbon Fiber tanks are extremely strong & robust. There are videos out there somewhere of guys shooting them & couldn't get the bullets to penetrate. I don't think there's anything you could do in the normal course of airgunning that would get them to fail.

Understood. It's mainly that I like the streamlined look and size of these narrower aluminum tubes vs. a bottle. The gist of my question is why aluminum is only said to handle 3,000 PSI but the S45 is rated at 4,500 PSI.

Example: https://www.bintacllc.com/product-page/bintac-b-w-s45-357-mini-9-inches-super-shorty-release-soon

Upgraded 350CC Carbon Fiber Front Tank Or Front 250CC and Rear 250CC Tanks [both metal cylinders - my comment]
Air Tube Capacity: 350CC Max
Air Filling Pressure: 4500 PSI

 

[Gerry52]

Don't forget that CF tanks are carbon fiber wrapped around aluminium & then resin coated over all. Not just carbon fiber. That's why the higher psi capacity.

 

[subscriber]

The gist of my question is why aluminum is only said to handle 3,000 PSI but the S45 is rated at 4,500 PSI.

Because that was the specs the manufacturer designed the tanks to. You could design an aluminum tank to hold 4500 PSI if you wanted to. It would have a proportionately thicker wall than one designed for 3000 PSI, at the same ID. That would make it proportionately heavier.

One way to avoid making an aluminum tank walls heavier, while still being able to handle high pressure is to reduce the ID. Generally, a long skinny tank can hold twice the pressure compared to a short one of twice the ID, at the same wall thickness. Of course one cannot see tank ID; only OD. So you have to take the tank's rated working pressure to mean what it says. Also, making a tank with its ID half the diameter of a comparable tank to enable doubling the working pressure, means it will have quarter of the air capacity, at a given length.

Aluminum is odd compared to steel with regard to fatigue life. Aluminum fatigues even when loaded to a quarter of its yield strength; while steel can have an almost infinite life at such low loads. In other words, filling a "bit over" the working pressure to get more air in is an especially bad practice with aluminum air tanks. Wait for the tank to cool, before adding more air. If you plan to use it in a hotter environment, then filling to less that the rated pressure would be the smart thing to do. Try not to exceed the rate working pressure. Not because the tank is likely to rupture then, but it makes it more likely to rupture later.


See fatigue endurance limit comparison between aluminum and steel:

Endurance Limit of Aluminum: Why Steel is the Unusual Material - Mentored Engineer

Steel and Aluminum are the two most popular materials when it comes to making structures. Yet, steel seems to win more. One of the ways that it beats Aluminum is

mentoredengineer.com

https://www.researchgate.net/figure/Comparison-of-steel-and-aluminum-fatigue-behavior_fig1_322220529

 

[AGN1023]

Don't forget that CF tanks are carbon fiber wrapped around aluminium & then resin coated over all. Not just carbon fiber. That's why the higher psi capacity.

That I didn't know. True across the board?

I also downloaded an AEA manual that lists the aluminum tank as "7075 aluminum alloy," and I found tables on its wall thickness vs. PSI strength. I suppose faith will suffice on this!

 

[HunterKillerBravo]

You can upgrade to the 500cc carbon fiber tank they have.

 

[Firewalker]

Yupper, I yanked the heavy aluminum tanks from my ANA'S and replaced them with carbon fiber.

 

[silvershooter589]

Haven't heard any reports of an AEA tank failing.

If you really want something to worry about, get a Defender 2.0 and fill up those carts to 5000 psi relying on an ultra thin burst disc to hold that air in. The fact that those miraculously do hold air and also don't fail in a dangerous manner makes me feel a lot better about tanks like AEA uses. They have some decent thickness and weight to them, plus a very large amount of threads screwing them onto the gun & for the end caps.

 

[bchannell]

One other thing to mention, and maybe I missed it, is that as you go up in pressure with an aluminum cylinder, the wall thickness is not linear. It would take some fairly thick walls to make a bottle that holds 4500psi, and it would be quite a bit heavier. My guess is that 3000psi or so is the 'sweet spot' in manufacture. I only have one rifle, and older generation FX Royale with an Al bottle, but it works great so I've never considered switching to CF. I do also have another Royale that is CF and reg'd, but guess which one gets shot the most....the AL version, don't ask me why, I just love that rifle.