GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: SpiralGroove on January 18, 2022, 11:19:47 AM
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If I used a standard co2 cartridge for a plenum, how many CC's are added to the existing set-up?.
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Found it on another thread - roughly 1.5cc's per gram or 18cc's for the standard 12 gr. cartridge.
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I was considering these threaded 16 gr. cartridges for a similar idea.
(https://m.media-amazon.com/images/I/815k3i3qADL._AC_SL1500_.jpg)
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Yes James,
Considering exactly that (I was thinking of threading), but would use the threaded 16 gram cartridge, enabling a 24cc plenum.
The big question for me is How much pressure is safe for the standard metal cartridge?
This could be done to my RAW (Air Force) PCP - by in-letting stock to accept (there is room). However, could I use a set-point up to 145 bar?
Most importantly, don't want to create anything unsafe.
If I can't use the co2 approach, how thick do aluminum walls (cylinder) need to be to withstand (2100 PSI+) 145 bar - safely?
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A 16 gr. CO2 cartridge adds about 20 cc to the volume.... I used one for a reservoir on my .25 cal Disco Pumper Carbine.... Reply #45....
https://www.gatewaytoairguns.org/GTA/index.php?topic=37401.45 (https://www.gatewaytoairguns.org/GTA/index.php?topic=37401.45)
(http://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/IMG_2725.jpg)
Detail photo above from Reply #16.... They are threaded 3/8"-24NF.... and you can drill the neck out (to at least 3/16") for more airflow to use as a plenum.... They actually have an insert pressed in, I drilled it out until the insert spun out, but I can't remember the drill size.... The drawing I got with my 16 gr. cartridges said the burst pressure is 500 bar, but CO2 vessels are normally rated at 1800 psi.... That would indicate a safety margin of 4:1.... A minimum of 3.5:1 is used by ASME for all pressure vessels.... That would work out to 2070 psi, with a 3.5:1 safety margin.... You should be fine at 145 bar....
Bob
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Thanks again Bob ;),
This set-up on my RAW HM1000X LRT (Airforce) should work in the stock between the M-Lok rail and 480cc tank.
Once set-up, out of sight/mind in a beautiful rifle.
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The threads on the cartridge are not tapered, so you will have to seal them by soldering or installing an O-ring somehow.... You might get away with glue or sealant of some kind, but I have never had success sealing HPA with those.... I soldered the cartridge into the brass gauge adapter on my pumper....
Bob
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The threads on the cartridge are not tapered, so you will have to seal them by soldering or installing an O-ring somehow.... You might get away with glue or sealant of some kind, but I have never had success sealing HPA with those.... I soldered the cartridge into the brass gauge adapter on my pumper....
Bob
Regular plumbing solder & flux …. aka sweating a copper pipe?
If yes, no sweat…🚀.
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Bob, I just checked .... regular solder won't hold high pressures.
What did you use?
Sounds like the o-ring option maybe best :D
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What about a flat bottom hole to use a bsp type seal?
Dave
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I used regular soft solder.... It's not holding a slip joint, like a copper fitting on a pipe.... it's only sealing the threads, which are supplying the strength.... I used resin flux(not acid) and tinned the threads, inside and out, and shook off/out the excess.... then heated the joint, threaded it in until bottomed, added a bit more solder on the outside to wick the joint full, and then let it cool....
Bob
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Thanks ;)
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If I can't use the co2 approach, how thick do aluminum walls (cylinder) need to be to withstand (2100 PSI+) 145 bar - safely?
Hi Kirk,
I know that your primary question has been answered, but wanted to make one point:
Wall thickness of a given material required to contain a specific pressure is not a contestant. It is directly proportional to the ID of the vessel.
The walls of a CO2 cartridge are thin, but that works because the ID is small. As soon as you make a pressure vessel 4 times larger in its ID (for example), the wall thickness must increase by 4 times to maintain the same strength and factor of safety.
There is a very simple method for calculating the "projected area" that the air pressure acts on, to try and "blow the lid" on the vessel. Bursting the tank across its diameter is the primary failure mode for small diameter tanks of a given volume. For larger diameter tanks the axial strength starts to become the limiting factor, because the "endcap" area increases with the square of the diameter. Whereas the projected area across the diameter is linear with the ID.
It pays to calculate both stresses, but for typical airgun tanks the limit for radial bursting is reached much earlier. That said, if an endcap at full tube ID has a very coarse thread, the tube wall may be thinned so much that it becomes the primary failure point.
With a necked bottle shape, such as a CO2 cartridge the area you connect to at the piecing end, is so small that the force on the (threaded or soldered) joint is so low, it is easily contained. Think about the thinner section that is actually pieced to let the CO2 out. That is strong enough to contain the CO2 "on the shelf" and during warm shipping. How can that work? Because the area exposed to gas pressure is small.
Other than stress due to air pressure, if the air tank is mounted via one end, I would consider its weight acting on the cantilever mount, and shock to the system on firing. For a CO2 cartridge this consideration is easily satisfied - compared to a horizontal 500 CC CF tank, for example.
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flat nylon washer below the canister, the canister crushes the nylon making a perfect seal every time.. Just like you may see on a HPA hand pump
what Dave said above.
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Guys
For what it's worth,
The average wall thickness of the 12gr Co2 cartridge is .035", from the several I have cut in half.
Somewhere on this site, I added a list of all the different Co2 cartridges/cylinders,
there is several sizes useable to us air gunners for conversion..... ;)
HTH's
Don
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Don,
What is the OD of such CO2 cartridges? I want to see if my calculation method reaches a valid max working pressure conclusion.
Thanks
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12 gr. CO2 are about 0.730" OD, they fit inside the 0.745" airtube easily....
Bob
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Sub
The ones I measured/cut in half (Crosman Branded) are .735" in diameter, give or take .001"...... ::)
I have several here that run from .728" to .731". they are old 10yrs + to the newest I got got last week.
HTH's
Don
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Thanks Bob and Don,
The attached screen captures are for two sections of air tank. The larger one has a .73 OD and .035" wall thickness, just like the CO2 cartridge body. The smaller one is half the size of the larger one in both ID and wall thickness.
The point of this exercise is to show that the ability of a given tube material to contain gas pressure depends on both the wall thickness and the ID. That if you reduce the ID by a factor of two, then you can reduce the wall thickness by a factor of two - without increasing the stress in the walls of the smaller tube, when containing gas at the same pressure as the larger tube.
This is a simple half-shell analysis, where an arbitrary section though the midline would be the same as any other section through the midline. An arbitrary one inch long section of constant diameter is considered, simply because it makes the calculations simple.
I chose 2070 PSI as the internal pressure to match Bob's safe pronouncement for a CO2 cartridge. My calculation of 19.5 kPSI stress in the walls at that gas pressure suggests that CO2 cartridges are not made from mild steel. But rather from a material with a yield strength of at least twice that of mild steel.
The red A, C and E represent benchmark data points for the CO2 cartridge size, while the red B, D and F represent the "half size tube" for comparison:
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=195444.0;attach=388247;image)
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Subscriber, if it helps any , there was a guy on the old green forum who hydroed a 12 gram to failure, burst occured at 9000 psi , the wall failed.
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Your calculations are pretty close to what you get for the stress using Barlow's formula.... My "pronouncement" of 2070 psi for a safe pressure was based on the manufacturers claimed burst pressure of 500 bar for the 16 gr. cylinders I purchased.... Your calculations were for a 12 gr., and I would point out that a 0.001" difference in wall thickness changes things quite a bit...
(https://hosting.photobucket.com/albums/oo221/rsterne/Important/.highres/CO2 16 gr_zpslpmokahj.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/a8f72a68-64d3-494b-98b3-85ba6a7a34e2/p/573a56b6-acf7-4054-9de8-a4280c749f43)
We do not know what the material is, and everyone has different ideas about what is "safe" and what isn't.... ASME requires 3.5X the working pressure for the minimum pressure for failure, but they only require a 1.5X safety margin to the "worst case" for yield.... I assume that is after years of fatigue, maybe a million cycles, and that depends on the material.... Steel typically has a "threshold" below which there is virtually no fatigue issues, and for most steels that is 50% of the yield stress (ie a safety margin of 2X using yield strength).... I use 2.5X the yield and 3.5X the tensile as my design point for pressure vessels, but a lot of guys use 3X the yield, which depending on the material may be 4X the tensile or more....
Bob
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Rob and Bob,
More data and info is useful. I agree that one does not know how close the strength of one CO2 cartridge manufacturer is to the others.
My assumption is that an AG pressure vessel should be 3X stronger based on yield strength. I don't like to use ultimate strength because once the parts starts to yield, it has already failed - in my opinion. It may be a safe fail; or fail safe to bulge in a manner that lets air escape past an O-ring, for example. Staying well below yield makes fatigue failure much less likely - more important with aluminum parts. So, more of a "how do I prevent myself falling off the roof" approach; than "how many bones can I break before I am out of action" :)
If a given batch of CO2 cartridges had a few samples bursts at 9000 PSI, then using similar ones to 3000 PSI as a plenum would seem almost OK. Although that is then 3X over ultimate strength, rather than the preferred 3.5 X over ultimate strength. Limiting such cartridges to 2500 PSI would be the smart thing to do.
It is possible to determine yield strength on a pressure test by looking at the gradient of a chart for the volume of fluid forced in as a function or pressure increase. When that near straight line (spring curve) starts to bend to a flatter gradient, yielding and thinning out of the material is starting to occur. If the test were paused there and the pressure released, the specimen vessel would have an increased OD, compared to before the test. To my mind, that is the info I prefer to use, with a 3X factor of safety. That said, rupture is a much clearer measurement point, that is hard to argue about. Just need to test more than one sample to get an idea of the variability before deciding what would be safe.
The question of fatigue becomes more important with "stronger" (harder) materials; where the yield and ultimate strengths are closer to each other. That, and a low "elongation at yield" are clues that the material is more brittle. Better to use a thicker wall of softer material, than can stretch a bit without blowing up. A bulged pressure vessel is a clear warning that you are looking for trouble, before actually running into catastrophic failure: A bulged gun barrel is a much better outcome, than one that splits, should one inadvertently shoot a bullet into one that did not clear the muzzle, due to a low powder charge...
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With the intent of using the CO2 cart as a plenum, it will see full fluctuation of the pressure from hi to low then back to high every shot, would this most likely shorten the service life?
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With the intent of using the CO2 cart as a plenum, it will see full fluctuation of the pressure from hi to low then back to high every shot, would this most likely shorten the service life?
not if its below a specific yield stress , which we dont know the exact number .( lets assume its 4000 psi ) so it would never in theory fatigue to failure as a plenum
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Guys
Here is some info on several type of CO2 cylinders/cartridges,
Lots of info about the spec's for each type, etc.
I have my mechanic friend looking for the car bottle, might make a good low pressure Air Tank.....LOL
http://www.lelandltd.com/disposable_gas_cyl.htm (http://www.lelandltd.com/disposable_gas_cyl.htm)
Tia,
Don
ps, Thanks to the member that sent me this info, it is greatly appreciated.
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Thanks, Don
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FYI -
The co2 cartridge thread is 3/8" - 24 per my die.
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FYI
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Alright Guys,
Finally got the plenum parts made using a 20 gram Co2 cartridge, so it should add about 25cc's to the existing RAW HM1000X plenum.
I contacted Martin at Airguns USA, but he couldn't give me the OEM plenum dimensions - likely around 25/30 cc's.
See pics of new plenum attachment ... with OEM plug it replaces. Tested brass plug before drilling hole for 38"- 24 thread and it holds air just fine using a 480cc bottle o-ring.
- Also have pics of where the stock will be cut to accept the plenum and longer brass plug.
I'll try to use Monster Pipe sealant, which under ideal conditions (pipe threads) is marketed to hold up to 3,000 gas pressure. Hoping this will hold on 3/8" - 24 (SAE) threads which aren't tapered. Fortunately, I only need it to hold about 2,100 psi or 145 bar ::).
Will put everything together in the next few days ;).
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As Bob had previous thought, the Blue Monster Pipe Sealant didn't hold the pressure for a moment.
Not even close :P.
- Will try soldering the 3/8" - 24 joint per Bob's method.
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Bob, I just checked .... regular solder won't hold high pressures.
What did you use?
Sounds like the o-ring option maybe best :D
It is not just the material hardness and strength that determines if a joint will hold air pressure. If the air pressure helps close the hole, a soft and "weak" material can work as a seal. Else rubber O-ring would not work.
With that in mind, a long narrow joint with lead solder wicked in should work. The force on the solder joint is the air pressure multiplied by a very narrow ring area. The much larger force trying to "spit out" the cylinder is carried by the threads.
So, providing the soldered joint is much deeper than it is wide, that should work fine. Assuming there is no pin-hole due to a lack of "wetting". But that is what joint prep and flux are for.
The above may be answering a question that has already been covered, but it is related to a common misunderstanding about what gas or fluid pressure a given material can stand. Just think of the brass case in a centerfire rifle. It seems like the material is not strong enough to withstand 50 or 60 kPSI. But the point is for the brass to expand, seal against the chamber wall, and let the barrel steel carry the load. The fact that it yields is what enables it to seal. The unsupported sections of brass (or O-ring in a PCP) have a very small area for the gas pressure to act on, and thus don't see more load than that material can support.
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Bob, I just checked .... regular solder won't hold high pressures.
What did you use?
Sounds like the o-ring option maybe best :D
It is not just the material hardness and strength that determines if a joint will hold air pressure. If the air pressure helps close the hole, a soft and "weak" material can work as a seal. Else rubber O-ring would not work.
With that in mind, a long narrow joint with lead solder wicked in should work. The force on the solder joint is the air pressure multiplied by a very narrow ring area. The much larger force trying to "spit out" the cylinder is carried by the threads.
So, providing the soldered joint is much deeper than it is wide, that should work fine. Assuming there is no pin-hole due to a lack of "wetting". But that is what joint prep and flux are for.
The above may be answering a question that has already been covered, but it is related to a common misunderstanding about what gas or fluid pressure a given material can stand. Just think of the brass case in a centerfire rifle. It seems like the material is not strong enough to withstand 50 or 60 kPSI. But the point is for the brass to expand, seal against the chamber wall, and let the barrel steel carry the load. The fact that it yields is what enables it to seal. The unsupported sections of brass (or O-ring in a PCP) have a very small area for the gas pressure to act on, and thus don't see more load than that material can support.
Thanks Subscriber ;).
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Straight (non-tapered) threads have a spiral shaped gap where air can pass....
(https://engineeringbonding.files.wordpress.com/2020/05/gap-between-threads.png)
All the solder has to do is plug that gap, as the strength of holding the part in place is taken by the threads.... The friction path retaining the solder in the gap is incredibly long (nearly 10" for a 3/8"-24 thread that is 3/8" long).... while the area that the pressure can work on to force the solder out of the gap is incredibly small (about 0.01 sq. in.).... While the same thing applies with a flexible sealant, if it can "flow" as all, it will eventually extrude out of the gap and you will get a leak.... A sealant that hardens (or a glue, like crazy glue) may work, or it may not.... If it isn't fully hardened, it will leak, and if the parts move relative to each other, it may crack and then leak....
Bob
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I love dropping in on these discussions. Rsterne, subscriber… reading those lasts posts about soldering threads, forces, materials filled a gap in my knowledge in a succinct and clear way. Happens most times I read your posts. I have no plans to do anything with a co2 cartridge… here at random.
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Hey Bob,
The Monster Pipe sealant failed immediately, so I soldered the joint this morning. I had trouble wicking the threaded Co2 cartridge, and especially the brass portion. I believe I did a poor job, not having done it before.
After cooling, the seal held for about 15 minutes, but then leaked. Need to reheat, disassemble and re-join surfaces.
I used a regular(blue) propane torch .... should I try using MAP gas instead? I don't think parts heated well or evenly enough for the solder to flow properly. I have the rosin flux and basic silver solder.
Any thoughts ............... I'm all ears :D.
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Silver solder requires more heat, and a totally different flux.... I used regular rosin-core electrical solder.... I tinned the neck of the CO2, wiped it off, tinned the inside of the brass adapter and flicked the excess solder out of the hole.... I then started the threads, heated the parts and turned them together, until they bottomed.... I then wicked in a bit more solder from the outside at the threads to insure the joint was full....
As with any soldering, cleanliness is key.... The flux is only there to exclude air from between the solder and the base metal to that they can form a bond.... Solder will not stick to dirt or an oxide layer.... If solder "beads up" instead of flowing, the substrate either isn't clean, or isn't hot enough.... In my experience it is usually the former....
Bob
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Thanks Bob ;),
Got some electrical solder w/rosin core which has a melting point of 361f (lead) vs. 430f (no lead) silver solder.
Will try to join again tomorrow...
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Kirk,
Solder needs to wet the parts. Your joint has globs attached on the outside, suggesting the metal was rejecting the solder, rather than wetting it to wick into the joint. Possibly due to an oxide layer, or some other contaminant.
I wonder if the plated CO2 cartridge is part of the problem. I assume it has cheap zinc plating, but it might be another metal. You certainly need to abrade the surface layer of the plating at the threads off, and proceed to flux and solder within minutes to minimize re-oxidation. I think abrasion is preferable to using acid to clean the zinc, rather than remove the zink. While the CO2 cartridge is probably work hardened mild steel, acid does nasty things to hardened alloy steels. Research "hydrogen embrittlement".
Try to minimize your exposure to breathing in the vapor coming off the hot joint. Zinc vapor can make you feel really sick, despite it being "good for you". Whatever you are doing to reduce or prevent breathing lead vapor is probably adequate. It is just that people don't know that welding galvanized steel can make them sick. I don't know if this applies to soldering, because the temperature should be much lower.
Anyway, the videos below might help.
https://www.youtube.com/watch?v=JyVbjDsric4 (https://www.youtube.com/watch?v=JyVbjDsric4)
In case of zinc plating:
https://www.youtube.com/watch?v=vwqGqcKa2j4 (https://www.youtube.com/watch?v=vwqGqcKa2j4)
https://www.youtube.com/watch?v=vMsi66MMkqI (https://www.youtube.com/watch?v=vMsi66MMkqI)
I would like to suggest that you practice soldering on sacrificial parts. When one "does it right", it works instantly. I have never soldered to zink, but it would oxidize fast because that is its purpose in protecting the steel underneath.
(I get lots of hits that the plating is zinc. For instance: https://www.co2cartridges.co.uk/12g-co2-cartridge-paintball-airgun (https://www.co2cartridges.co.uk/12g-co2-cartridge-paintball-airgun))
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Thanks again Subscriber ;).
Will take in the videos before proceeding....
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I would think pre tinning the threads then screwing together after cooling could supply the needed sealing surfaces, think old lead seal on old pumpers ???
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Hey Guys,
Got a day off .... re-soldered plenum parts with electrical solder and it's Holding Air ;).
Thanks Bob 8) and subscriber & everyone else for input.
Also, used a 16 gram cartridge as this is my .22 caliber RAW.
The plenum should now have about 45cc's (25cc's OEM + 20cc's) of air on-board ... and should provide enough oomph for 60 FPE
- if necessary ::).
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(https://www.irishtimes.com/polopoly_fs/1.4473007.1612185073!/image/image.jpg_gen/derivatives/box_620_330/image.jpg)
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Here's a few pics:
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That works.
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Great job!.... 8)
Bob
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Kirk
Ya done GOOD........ ;)
Tia,
Don