Rear tank gauge
Hi All,
First time here…
Reading some posts over the last couple of days, learning and having fun simultaneously, I decided to tell also my experiences.
I think that for a PCP tank, a gauge is a must.
Although I have used the gauge mounted in the neck of the bottle, it does not pleasing me 🙄 for two main reasons:
1º The gauge in the bottle neck is very small, and difficult to read (and the useful zone of reading even more) and I believe that it is not accurate enough.
2º I dont like the the asymmetric protuberance of the gauge in the bottle neck turning around while I screw the tank on. I see it fragile and dangerous if it receives a blow.
Then I decided to mount a real good gauge in the only position that is possible: the bottom of the bottle.
To do it, is indispensable to do drill a hole in the thank ( this is forbiden in some countries), but as a experiment I decided to take the risk, but with the due precautions of safety .Please note that I don´t say to anybody to do that.
The first thing of all, to locate a suitable gauge. In my case I had to order it do, since I did not find what was searching in the shops of pneumatic and hydraulics.
In two weeks they made a gauge of 40 mm of outside diameter and 250 Bar on a large scale, with a rear thread of 1/8 G and 11mm length:
After, measure and verify the thickness of the bottle bottom wall,mesuring the outside and after the inside, I found that the wall thickness is 7 mm. More than enough for my purposes.
Afterwards, centre the tank on the lathe as best as possible and drill and thread the wall of the bottle….Yes, as natural as it sound , a hole in the bottom. 😀
For cutting the thread I help my self with a little drop of cutting fluid.
Nevertheless I do not want to allow that the whole pressure of the tank should push on the threads of the gauge and I decided to install a nut from the interior to hold safely the gauge. It has also an O ring to avoid leaks: 😉
I had to do also the special key for this nut:
To install the nut inside the tank with the special key, was tricky and difficult due to the narrow space, and especially because you work blindly!! 😕 😕 😕
Once installed the gauge and its nut, I protected the whole assemble with a cover of aluminium specially designed to embrace the tank and to protect the gauge of possible shock and blows.
In addition it gives more resistance to the whole set. And it gives me the confidence of not having the gauge sticked into my shoulder.
Before installing it, I tried that the gauge fits very nicely inside its new housing:
Once quite mounted, the test-proof of pressure was satisfactory, I sprayed the tank rear with soapy water,charged the bottle very slowly, no bubbles at all, and for 20 days I left the tank loaded on 200 bar without losing only one bar of pressure. 😀 😀 😀
Already I have neither to count pellets nor do calculations simply I begin to shooting in 185 bar and finish on 100 bar. With good consistency of speed. I also have a good control of the presure while charging from the scuba. 8)
At the same time as I began this project, also I did an anatomical butt adjustable in length and height to do more ergonomic the set. Also it protect the glass gauge when not in use.
The screws that hold the support of the butt to the bottle are nylon pointed, to not damage or to create points of pressure on the surface of the tank
And this way there stays the whole set mounted and ready to shoot.:
Postscript
I do not recommend to anybody to do the same thing that I have done, since this is potentially dangerous specially if you dont have the proper tools….And knowledge
Each one calculates his own risk and do in consequence
Hope you like it
All Replies
These tanks are mass produced and as such Im willing to bet that they are over engineered to err on the side of caution. As you said, they do not run each tank through those extensive tests to verify its structural integrity. They most likely do simple tests on say one in a hundred tanks and if those pass the whole batch gets the Aok. Im also willing to bet that you could take two tanks of the same type and cut them in half and there would be irregularity’s between the two or even in its own thicknesses. If youve ever seen how these tanks are produced you would probably be surprised. They take raw materials and heat, spin, stretch, pound and stretch some more until they are the right size.
Another thing I dont understand. Why do folks get uptight about the threads holding? I have recently been sourcing out high pressure gauges. Ive looked at dozens and they all have about a 1/4 inch of thread in about the same sized hole. Many of these gauges are rated for over 5000 psi. I havent heard of a big problem of the threads shearing and the gauge shooting across the room. I think Xaloc has gone far beyond what is required to hold a gauge like that under pressure. The only thing in question is the tanks integrity. For that all I can say is look at the guy installing fill adapters in an almost identical tank. He has had no tank failures. Ideally someone should drill one and then have it re certified.
But you can drill holes in a structural shear wall… 😉
The diaphragm doesn’t have to be untouched, it just has to retain enough strength to hold up the building (allowable penetrations in shear walls will be a drawing in the engineers set of plans)…
The hole at the bottom of the tank could be within the allowable parameters… Only testing or an engineer could tell you for sure…
The main point is that we can speculate either way and most have speculated towards the negative. It could be perfectly fine, but we will not know until it is either tested or calculated by an engineer familiar with this type of application……
Stepping back and looking at the DOT certification process brings up a lot of questions and there seems to be some leeway in the process to account for structural manufacturing flaws and abuse of the tanks…
I don’t see magnaflux testing or the xraying of tanks to confirm the integrity of internal metal lattice structures and to look for any micro fractures in the manufacturing process for each tank…
I’d bet dollars to doughnuts that if you paid an engineer to figure this out his response would be very different than that of Catalina Cylinders. And if there was a serious money making potential Catalina Cylinders would change their tune and look at it instead of dismissing it outright.
When someone dismisses things outright they usually have an ulterior motive or they don’t want to take the time to take a real look…
After all it hasn’t exploded yet… 😕
The houses I work on usually require the engineer to sign off the job, he has got to cover his ass by inspecting the craftsmanship of the work There are limitations on how much you can cut up a shear wall before it will fail, if you start cutting the shear panel it becomes weaker with every penetration you make. So, my opinion if you drill a hole in a high pressure tank it becomes weaker.
Don’t get me wrong the guy has a great idea, there are lots of guns out there that have a gauge on them, and I think one on the airforce guns would be a good feature. However putting a hole in a tank that you rest your face on is not, until proven.
Saw, that applies IF your minimizing the shear wall sizes. If you have a house fully engineered (which is expensive) you are allowed a lot more penetrations in the shear walls and leeway in it’s seismic design. For two story residential there is a bit more room for error in the engineers calculations.
I’m sure you have worked with TJI’s, have you noticed how much you can cut a 9.5″ TJI before it is unsafe.
Now when you build a tower, say 20 stories or more then things become a bit more critical and the engineer has to sign off on a slew of items before the rest of the construction can begin.
I personally like to cover the entire house in shear ply, I sleep better knowing my clients will most likely survive the next big one… Why, see below…
An engineer’s art it to design things just strong enough to work under typical operations (with earthquakes, what exactly is the loading??). Take sizing a beam for example, unless there is a damn good reason an engineer will not oversize a beam, it would be considered ‘ugly’ to them…
I certainly think if the tank was designed for hole to be drilled and tapped this venture would be production worthy.
If it were me I would make two tanks exactly the same, one I would send out and have it pressurized until it explodes and see where and when it breaks, if it were safe enough from the testing data I would use the second tank…
Voltar, what kind of pressure were those things running at? Wow! And sometimes we may disagree but I will always take your words as good sense and solid knowledge from some serious experience…
Now I really want to know where an AF tank will burst. 😆
the slip blind is not a good analogy.
1. A center punch creates a flaw, that along with a tensile stress and low fracture toughness will cause any mmeatal to fail.
2. Your welder , just by the use of the torch ,metalurically altered the steel.
3. was the steel of the proper material and thickness to begin with?
The use of a lathe to drill the bottom of any “turned Tank” or as you say “spun” will actually make the tank stronger by removing the area flawed by the tail stock.
A nut on the inside along with threads seems to reasonably mitigate any threat of ejecting the fitting.
I dont think this man is trying to give DIY instructions to harry homeowner with a cheap chinese lathe. He is obviously skilled and educated.
now i think catalina and dot gave good advise.
It takes tens of thousands of dollars to get an organization qualified to repair a pressure vessel in the U.S. and with good reason.
Thank god, you sir, were not around in Ben Franklins days. You may have curtailed a lot of innovations.
Now that is amusing. I am an innovator, maker, perhaps you missed all that.
Cheers,
Walter…
voltar:
the slip blind is not a good analogy.
1. A center punch creates a flaw, that along with a tensile stress and low fracture toughness will cause any mmeatal to fail.
2. Your welder , just by the use of the torch ,metalurically altered the steel.
3. was the steel of the proper material and thickness to begin with?
The use of a lathe to drill the bottom of any “turned Tank” or as you say “spun” will actually make the tank stronger by removing the area flawed by the tail stock.
A nut on the inside along with threads seems to reasonably mitigate any threat of ejecting the fitting.
I dont think this man is trying to give DIY instructions to harry homeowner with a cheap chinese lathe. He is obviously skilled and educated.
now i think catalina and dot gave good advise.
It takes tens of thousands of dollars to get an organization qualified to repair a pressure vessel in the U.S. and with good reason.
Thank god, you sir, were not around in Ben Franklins days. You may have curtailed a lot of innovations.
I maintain that this guy is a fool and has no clue regarding the safety of his venture. There is no call to applaud this period.
Think of it this way:
The tank is drilled and tapped AND a threaded nut is inserted through the tank top. This nut will be 16mm in diameter say 0.630″ and the tap for 1/8npt is 0.400″ leaving a wall on the nut of 0.065″.
Now to top it all off a 1/8″ gauge has but 1/2″ of threads available so how much good is the nut? How thick or thin must the tank bottom be to allow the use of that nut?
Here is a real example when I worked in a gas plant. We would isolate systems by the use of a pancake blind. After a series of failures regarding these blinds it was determined by a metalurgist that the center punch mark in the center of the pancake used by the weldor to cut the circle weakened the blind to the point of failure.
They were forthwith abolished from use and only perfectly flat blinds are permissable now.
I say this is a foolish idea. He is definitely not the first to try this as there is a guy doing fill fittings in the bottoms of Rapid tanks.
Not a real good idea either!
Walter….
No engineer here by any means.
However in house construction, we have shear walls.
These are walls that are built for lateral resistance, usually 2×4, 2×6, whatever.
There are certain rules applied to such, how big a hole ect….
These walls are considered structural. There are specs. to how the shear panel is nailed to the wall, with how many nails, spacing, nail penetration.
Us in the house building trades call them diaphragms.
When you drill a hole in the bottom of a hpa tank you are breaching that diaphragm.I believe the hpa tanks are spun, could be wrong ?
The person who put the gauge on his tank is a smart man, but consider what happens to the metal of the tank when a hole is drilled into it.
Metal fatigue what ever?
Is it really worth having a gauge on your tank ?
Until they produce such a thing, I am willing to wait.
I however plause the gentleman for his innovative thinking.
I’m not knocking them for what they have to do, you said it best, they have to respond like they did…
And they are going to say this until they come up with an idea that works (like this one could) and then they would stand behind their product…
DOT certification is just a pressure test from all the links I clicked on… (And I am hoping I am wrong on this…) Why do I hope I am wrong, read below…
What guarantees the metal’s structure for each tank? Even the best manufacturing processes have problems…
Say there is a manufacturing defect so that the tank passes it’s initial certification, 100 cycles later it bursts (# of cycles fall under the re-certification time limit)… The thickness of metal is probably sized to allow for this problem… Typically structural building steel is loaded to no more than 60% of it’s breaking strength to account for such inconsistencies…
Is the DOT cert test going to find all the potential problems? Does it guarantee that every tank will work within it’s requirements, hell no!!! I would bet that the DOT assumes no liability for their determination that if a tank meets their certification test that it will operate without failure for the life of the certification…
Let’s say DOT tests a tank for cycles to bursting, there is still nothing that assures that the metal is the same for all produced tanks (obviously you can’t test them all to bursting)…
I think that if you screw the valve off and on many times you could have a fracture issue at the area where the valve screws in and out (granted that you load up the threads with a decent amount of torque). DOT doesn’t test this it just test the tank and probably even without a valve in it…
Either way there is obviously a huge fudge factor built in for all this HPA stuff…
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How about an intuitive comparison (I believe this is legit), I weigh about 250lbs, if I stand on a 1″ square footprint that is 250psi…
If I stand on a pencil sized stick it is about 1000psi.
If I stand on a footprint about the size of this “o” it is about 3000psi, now imagine me standing on the tank with a contact patch the size of an “o”…
How many more of me would it take to puncture an empty tank?
I bet you could put 6000-7500psi into an AF tank before it will go boom…
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An interesting number to see would be the area of thread contact in the rear mounted gauge (IIRC this determines the loading on the edge of the tank and this area would be the most likely place for a problem, not enough grip to hold the gauge, valley of thread begins to stress fracture, tank tears from the threads out…).
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Like I was saying, there appears to be a huge fudge (read: insurance) factor in HPA and it’s certification… Or the certification process is severely lacking (but full testing would be cost prohibitive)…
Not trying to argue with you Voltar, but do you really think he threw the rules out the window? I’m just trying to look at this from all angles and very much looking forward to your response… 😀
Well what do you think?
There is about 3,000fpe available in that tank and if released due to a fracture that tank will open like a bananna.
Don’t be so quick to knock safety ‘experts’ and tank vendors. They have rules imposed on them for public safety.
Experimenting and saying to hell with rules will bite someone someday and you better hope beyond hope you are not the one liable.
Walter…
Will the tank really go boom or just hiss?
Most stuff I can find does not point towards an explosion (unless you mix oil…)…
FACTIOD REGARDING “PROFESSIONAL”, “EXPERT”, and “ENGINEERING”…
NASA engineers said it was “IMPOSSIBLE” for a piece of foam to break through the carbon fiber leading edge of the shuttle’s wing…
And you would think these are the best and brightest at what they do… 😉
Shit happens, and when it does all the “Atta Boy’s” in the world cannot always make it better.
Many safety rules are not just for the person who is involved but also for the safety of innocent bystanders.
I think his modification is great. But that does not mean much if a hairline crack starts and one day splits the tank while next to a face.
Shadoh,
The D.O.T and Catalina are the ones that test these on a ongoing basis. They are going by experience in tank safety not so much “I think it is OK” as the rest of us do.
Xaloc mod is impressive and it is his own as he has stated. The other side is in the U.S.A that modification is illegal. Since he is in Spain it is his call. But for us State Side it is federally regulated on how these tanks are used.
They will say this UNTIL they come up with a similar item from which they can make $$…
Lots of breakthroughs come from people doing things the ‘experts’ say is impossible and dangerous, then it becomes common practice after some time…
It’s nice to witness breakthroughs and the resulting clamor of the naysayers…
Most of the time it’s what tells me I am on the right track… 😉
Guys I have been following Walter’s airgun work for a few years now and had the pleasure to meet and shoot with him a few times. I invited Walter to meet with good friend of mine who owns a CNC/Machine shop that produces aircraft and racing parts. Now the owner of this shop after inspecting Walter’s work and conversing with him came away with a high level of respect for Walter’s abilities on both machining and vessel theory.
I will not go into too much detail about Walter’s qualifications all I will say is he is more then qualified when it comes to high pressure vessels and I mean from a Commercial sense not a hobbyist sense.
Even though his comment may have sounded harsh it was more of a direct approach which was needed to induce debate because if someone with little experience or no commercial experience attempted this mod and an injury or death was the result we all lose.
So in reality we just have someone who does not want anyone hurt by trying to copy an idea, and taking shortcuts or making guesses.
I for one want and expect to hear the pros and cons on this Forum (polite on not) as ultimately we are a collective that frequent here to learn.
So thanks Walter and everyone else for sharing your opinions.
And NO I am not a relative of Walter’s just an Airgunner who has been shooting AG’s for over 35 years now and wants to continue to learn.
Randy
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Damn it Shadow, you said exactly what I was thinking in half the sentences… 😆