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Author Topic: Air tube fabrication  (Read 407 times))

Offline BeauJames

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Air tube fabrication
« on: October 13, 2021, 10:53:12 AM »
Need to make a new airtube assembly for my Kral NP02. Iím going to a little longer barrel and want the airtube to match. Iíd like to see the new airtube be good up to 4,500 PSI and rework my valve in the future. Donít know how doable that is. I work in a steel shop, and we do pressure vessels so I have a wealth of knowledge around me. We donít do small pipe/tube pumped to 4K though. We also have a couple machine shops that do work for us, theyíve done a few projects for me. Any metallurgist on here with a recommendation for material and wall thickness. Iíve got code books to go off of, but they donít tell me this 1 1/2Ē S/40 pipe with this thread on both ends is good for xxxx psi. I can hydro pressure test it also if need be.

Thanks for any and all help.
Beau Moody
  • USA, Oklahoma, Locust Grove

Offline TroyHammer

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Re: Air tube fabrication
« Reply #1 on: October 13, 2021, 12:31:53 PM »
The tube on the NP03 is aluminum not sure about the 02. Any pressure over 3600psi will likely need a reg.  Hard to get it consistent shot to shot starting that high with out one due to valve lock or you end up with a cliff tune. OD of the tube is nearly identical to the bulldog and I think they're using 2024-T3 for the higher pressure tubes but still 36-3800psi is the most pressure recommended even then.
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Offline sb327

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Re: Air tube fabrication
« Reply #2 on: October 13, 2021, 12:48:59 PM »
Hereís a handy calculator I use quite frequently. Remember to change the safety factor as well.

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

I think most folks use 3.00 sf for yield strength

Or

5.00 sf for ultimate tensile  (you might check those numbers out to make sure, hopefully Bob chimes in)

Having that figured out THEN find the properties of the material you had in mind.

Buy from a trusted source

Dave
« Last Edit: October 13, 2021, 12:51:42 PM by sb327 »
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Offline BeauJames

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Re: Air tube fabrication
« Reply #3 on: October 13, 2021, 04:39:51 PM »
Thanks guys, the gun will be regulated. And the high pressure is not all that important to me. Since it has a 4500 psi bottle and Iím making a new air tube why not make them to match, if it doesnít cause a whole list of problems including cost of material.

All material will be bought through our vendors at the shop.

Troy, to regulate the gun Iím assuming the bottle needs a reg and the front air tube needs a reg, or a reg on the bottle and the front tube becomes a giant plenum? Am I correct in my way of thinking. Sorry new to dual air reseviour guns?
  • USA, Oklahoma, Locust Grove

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Re: Air tube fabrication
« Reply #4 on: October 13, 2021, 11:56:10 PM »
Beau,

One has to assume the regs will fail (because they can and sometimes do) and the tube will see the full reservoir pressure.  So, good call on making all parts robust to the same level.
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Offline TroyHammer

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Re: Air tube fabrication
« Reply #5 on: October 14, 2021, 04:26:07 PM »
Beau,

One has to assume the regs will fail (because they can and sometimes do) and the tube will see the full reservoir pressure.  So, good call on making all parts robust to the same level.

The Kral valve has a burst disk so it will blow if it sees much over 3000psi that should help with the tube seeing tank pressure due to reg failure.
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Offline BeauJames

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Re: Air tube fabrication
« Reply #6 on: October 15, 2021, 09:57:26 AM »
Subscriber
I didnít think of it in terms of reg failure, even with the burst disk in place it would be nice not to worry about it. I was going to make it as strong, just so I had the option.

How do I regulate it? The gun of course fills from the front fill valve on the air tube, which fills the bottle also. The bottle is connected to the air tube on the valvebody outside the the air tube, via small copper line. It seems just by looking at it that a standard regulator in the air tube, like the Huma I have in my PB, wonít work. It would only allow my bottle to get the set reg pressure. So that puts me at regulating the bottle and the air tube only being a plenum. Am I missing something? I havenít had this gun stripped down and the valves out, but everything seems to be standard Kral Puncher.
« Last Edit: October 15, 2021, 10:00:26 AM by BeauJames »
  • USA, Oklahoma, Locust Grove

Offline sb327

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Re: Air tube fabrication
« Reply #7 on: October 15, 2021, 10:17:06 AM »
Can you post a picture? Kinda curious about the Ďsmall copper lineí. Not saying itís not sufficient but just curious I guess.

I see what you are saying about the arrangement leaving only the bottle air unregulated. If thatís the case, like you said, youíll just have an extra large plenum.

Dave
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Dave

Offline BeauJames

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Re: Air tube fabrication
« Reply #8 on: October 15, 2021, 01:09:19 PM »
It wonít let me post a picture. I thought it was my cell service/internet which is pretty bad, but I canít get it to post in town either. Iíve posted a few pictures on here before with no issue. Iím going to take different pictures when I get back home.
  • USA, Oklahoma, Locust Grove

Offline BeauJames

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Re: Air tube fabrication
« Reply #9 on: October 15, 2021, 01:30:30 PM »
https://canadashootingsupply.ca/wp-content/uploads/2021/08/brassairline.jpg

Hereís the copper line. The ends are turned up to a 90 and connect the bottle block to the valve. Iím working on pictures.
  • USA, Oklahoma, Locust Grove

Offline sb327

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Re: Air tube fabrication
« Reply #10 on: October 15, 2021, 03:27:11 PM »
I see. Thanks

Dave
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Offline TroyHammer

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Re: Air tube fabrication
« Reply #11 on: October 15, 2021, 04:04:45 PM »
You'll want a bottle regulator. They have their own foster fill nipple so it will eliminate the need to fill from the front with a probe. Only issue is it lengthens the shouldering of the gun.  Possibly a shorter bottle.  I have an aluminum 4500psi bottle that's only 350cc. If you found something like that it shouldn't make much difference.
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Offline BeauJames

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Re: Air tube fabrication
« Reply #12 on: October 15, 2021, 04:06:12 PM »
Dave,

I just noticed youíre in Stigler. Iíve got quite a bit of family down that way. Mainly Eufaula and Keota. Beautiful country. I canít get it to post, it even let me upload a picture for my avatar, but wouldnít let me in a reply.
  • USA, Oklahoma, Locust Grove

Offline BeauJames

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Re: Air tube fabrication
« Reply #13 on: October 15, 2021, 04:07:24 PM »
I didnít think I had a photo attached to the last reply, guess it decided to work. Hereís a better one.
  • USA, Oklahoma, Locust Grove

Offline BeauJames

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Re: Air tube fabrication
« Reply #14 on: October 15, 2021, 04:15:40 PM »
Troy,

Iíve got a short bottle on it now. .25 liter so it shortened the length of pull for my oldest son to shoot. Itís short for him with the stock slid all the way in, so hopefully the regulator wonít get it to long. Thanks for the help guys.
  • USA, Oklahoma, Locust Grove

Offline sb327

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Re: Air tube fabrication
« Reply #15 on: October 15, 2021, 05:10:41 PM »
Sounds like you got friends/family on both sides of me. I actually live pretty close to the dam.

It also sounds like Troy said on the reg. Go with the one on the bottle.

Thatís an interesting gun there. Looks pretty solid.

Dave
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Offline BeauJames

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Re: Air tube fabrication
« Reply #16 on: October 15, 2021, 07:17:33 PM »
Yes sir, sprinkled all along eastern Oklahoma. Thatís a good place to be. I lived outside Eufaula for a bit early in my marriage, never got on the striper below the dam. Caught a lot of crappie out of the lake though.

Thatís what I figured it would end up being. Itís a cool little gun, very handy. I wasnít sure how other guns configured this way connected the two reservoirs, seems like a simple solution and itís worked well so far. Itís a .25 and the most I could get with hammer spring adjustments is 680 with 25gr JSBs. Iím waiting on parts to convert it to .22 with a 16Ē barrel. Very accurate in .25, just want a little more velocity.
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Offline TroyHammer

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Re: Air tube fabrication
« Reply #17 on: October 15, 2021, 09:42:23 PM »
Yes sir, sprinkled all along eastern Oklahoma. Thatís a good place to be. I lived outside Eufaula for a bit early in my marriage, never got on the striper below the dam. Caught a lot of crappie out of the lake though.

Thatís what I figured it would end up being. Itís a cool little gun, very handy. I wasnít sure how other guns configured this way connected the two reservoirs, seems like a simple solution and itís worked well so far. Itís a .25 and the most I could get with hammer spring adjustments is 680 with 25gr JSBs. Iím waiting on parts to convert it to .22 with a 16Ē barrel. Very accurate in .25, just want a little more velocity.

My 25 is getting 880fps with 25.4gr with the 16" barrel. A new power adjuster, porting and a new hammer spring will get you there.
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Offline BeauJames

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Re: Air tube fabrication
« Reply #18 on: October 16, 2021, 01:54:15 AM »
Iím gonna get there with it. I need one of your power adjusters. I watched your video trying to keep up with the RAW. Good job by the way.

I have a large Jet drill press on a pedestal with a vise and bits/taps at work to do the porting. I havenít been confident enough to drill my transfer port and valve out. I know itís fairly straightforward, and Iíve got experienced guys around me, I just donít want to ruin a part not easily replaced. Iím still lacking a little info on how to also.

Weíre in hunting season now and with my .22 cal PB parts on it, it pushes 16gr AA at 870. Iím hoping for around 830 with the 16Ē barrel. I have quite a bit of 22, and very little 25 right now also, so it will do until Iím ready to really dive in. I need to do my PuncherBreaker also.

I need a good start for springs if anyone has a recommendation. Iíd like to have multiple different weights to experiment with. Iím trying to learn the tuning and modifying process. I love tinkering, still green in this arena.
  • USA, Oklahoma, Locust Grove