Ever wonder how strong an airtube really is?

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Hajimoto

Hajimoto

Member
Oct 23, 2016
1,080
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Wilbraham Massachusetts, United States
hajimotoproductions.com
As most of you know I am a MROD owner and fan. I have added a Huma Reg and a bunch of other tweaks and modifications to the rifle. See the below photo of her in her full Night Sniper glory :)

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Well with the IR lights, Screens, Batteries, Scope Camera, Scope, Bipod and other little doodads the rifle weighs in at a whopping 14 pounds!
So in looking for ways to shave off some weight I came across a new lightweight air tube that is available and they shared some of their pressure testing sessions.

Take a look at this, it is nuts! This ole boy will shave 1.5 pounds off the MROD, Woo Hoo!

 
"BeachGunner"Yea, I saw this Haj. Pretty remarkable. Glad to know there could be a 3x safety margin of the stated tube. 
It would be cool to see someone do this with a higher rated tube like a Cricket or Taipan which says they can be filled to 300 bar, I think?
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Are you volunteering a Taipan Beach???? LOL 
 
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"cilami"Impressive. Lloyd's videos are always very interesting... and convincing.
By the way, Haji, what recording device do you have in your NV system?. Your setup looks really nice. I am still looking for a good solution to record my night shooting videos.
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The NV setup is a Hajimoto Scope Cam Assembly. You can watch how I did it and build one yourself :) When you are done you can do the following including Infrared Night Vision.
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Here is my Build video and a video of the night capture. All light seen in the nighttime video is Infrared floodlights. To the human eye, it was pitch black.
 
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Nice to see the ability to lower gun weight (for us older guys) for a field gun. I thought I had seen this before and I found the post.

http://www.airgunnation.com/topic/most-compact-marauder/

I know I had seen recommendations somewhere when Matt was doing his build about adding an additional valve screw due to the "softer" aluminum, but can't find it now. I wonder are these tubes just "drop in"? or is there an additional valve retention screw?
 
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I had a custom aluminum air tube done to my marauder 6 months ago thanks to a forum member here Vash that fabricated the tube with his amazing cnc skills. I paid around 140$ for the work including materials. I am glad Lloyd confirmed all the calculations I did prior to following through with this. The first time I filled my tube was a little nerve racking.

I didn't add any valve retention screws or anything but was recommended to do so by others on another forum.

Glad to see others being able to enjoy the ideas I brought to the marauder platform :) The 1.5 lb difference is huge and you couldn't pay me to go back to the chromoly tube.

This tube is just shy of a 3.5x safety factor being it failed at 10k which makes it 3.3x safety factor but in my book that is good enough...I believe the marauder tube in factory form can withstand the full 3.5x and possibly even 4x prior to failure. I actually expect potential failures on these tubes to be around 2.5-3x which means in some cases these tubes may blow at or around 7500-9000 psi, especially if you were to repeatedly fill and empty the rifle at those levels. FWIW

-Matt
 
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"ackuric"I had a custom aluminum air tube done to my marauder 6 months ago thanks to a forum member here Vash that fabricated the tube with his amazing cnc skills. I paid around 140$ for the work including materials. I am glad Lloyd confirmed all the calculations I did prior to following through with this. The first time I filled my tube was a little nerve racking.
I didn't add any valve retention screws or anything but was recommended to do so by others on another forum.
Glad to see others being able to enjoy the ideas I brought to the marauder platform :) The 1.5 lb difference is huge and you couldn't pay me to go back to the chromoly tube.
-Matt
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OK, so I wasn't dreaming that. I had thought I heard about a recommendation of adding a screw to the value retention so the tube would not "rip" or the holes "elongate" due to the softer aluminum (compared to the steel).

Nice to see guys everyday average airgunners coming up with innovative ideas for these basic guns.
 
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"Hajimoto"
"AirGunShooter"Hajimoto - Have you ever performed a hoop stress calculation on an air gun pressure tube to determine the allowable pressure at the material's stated yield strength?
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No sir I personally have not. Sorry

It was just curios if you were in any way involved with the pressure test video?

Early in the video when tube diameter measurements were taken after the first pressure cycle and it was noted the change in diameter, the material had already yielded. When designing and working with high pressure materials to be used with a compressible fluid, we consider a yield of this magnitude to be a material failure. Any time an item is stressed to the point of exceeding the specified minimum yield strength of that material, the item has officially failed. Testing to ultimate catastrophic failure is certainly important, but it is not a point I would ever want to use in the real world safety design rating of a product. Hopefully those doing the video performed a calculated yield point to use for predicting material failure and fatigue related cycles. 
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"Hajimoto"
"BeachGunner"Yea, I saw this Haj. Pretty remarkable. Glad to know there could be a 3x safety margin of the stated tube. 
It would be cool to see someone do this with a higher rated tube like a Cricket or Taipan which says they can be filled to 300 bar, I think?
Click to expand...
Are you volunteering a Taipan Beach???? LOL
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I wish I had one to volunteer!! 
 
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"AirGunShooter"
"Hajimoto"
"AirGunShooter"Hajimoto - Have you ever performed a hoop stress calculation on an air gun pressure tube to determine the allowable pressure at the material's stated yield strength?
Click to expand...
No sir I personally have not. Sorry
It was just curios if you were in any way involved with the pressure test video?
Early in the video when tube diameter measurements were taken after the first pressure cycle and it was noted the change in diameter, the material had already yielded. When designing and working with high pressure materials to be used with a compressible fluid, we consider a yield of this magnitude to be a material failure. Any time an item is stressed to the point of exceeding the specified minimum yield strength of that material, the item has officially failed. Testing to ultimate catastrophic failure is certainly important, but it is not a point I would ever want to use in the real world safety design rating of a product. Hopefully those doing the video performed a calculated yield point to use for predicting material failure and fatigue related cycles. 
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Reallllly????? Do you mind if I grab your comments so the seller can respond to me? I have already ordered it but i do not want plagiarize the comment either that or you comment directly, Thanks.
 
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"Hajimoto"
"AirGunShooter"
"Hajimoto"
"AirGunShooter"Hajimoto - Have you ever performed a hoop stress calculation on an air gun pressure tube to determine the allowable pressure at the material's stated yield strength?
Click to expand...
No sir I personally have not. Sorry
It was just curios if you were in any way involved with the pressure test video?
Early in the video when tube diameter measurements were taken after the first pressure cycle and it was noted the change in diameter, the material had already yielded. When designing and working with high pressure materials to be used with a compressible fluid, we consider a yield of this magnitude to be a material failure. Any time an item is stressed to the point of exceeding the specified minimum yield strength of that material, the item has officially failed. Testing to ultimate catastrophic failure is certainly important, but it is not a point I would ever want to use in the real world safety design rating of a product. Hopefully those doing the video performed a calculated yield point to use for predicting material failure and fatigue related cycles. 
Click to expand...
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Reallllly????? Do you mind if I grab your comments so the seller can respond to me? I have already ordered it but i do not want plagiarize the comment either that or you comment directly, Thanks.

PM sent.
Click to expand...
 
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According to my calculations this tube can and should yield (fail) at around 7600 psi...which makes a working pressure of 2500 psi @ 3x safety factor for those who are curious. I personally use a similar tube and am fine with only a 2.5x safety factor on yield which gives a working pressure good up to 3040 psi.

You can check for yourself here:

https://www.engineersedge.com/calculators/pipe_bust_calc.htm

For those who are used to over filling their marauder tubes to 3200~ for a few more shots, I highly advise against this as the cyclic damage my add up and that is only a safety factor of around ~2.37x

FWIW: Yielding is defined as the material changing shape/dimensions under load permanently. IE: You have 1.25" OD and the material stretches to 1.26" and doesn't return to 1.25" OD when empty.
 
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