Air Arms Why you shouldn’t overpressurize your S4xx/5xx
- Thread starter Sawney Bean
- Start date
The video below shows an air tank being destructive tested, using air, inside a robust test chamber.
The chamber door is distorted after the bang, because of the amount of energy released.
If your PCP air tank can enable you to shoot 100 shots at 30 FPE, and the overall efficiency is 50%, then the energy contained in that air is over 6000 FPE (because you do not shoot it down to zero). If all the air in that tank is released abruptly by rupturing the tank wall it has the potential to do a lot of damage. Way more than would happen in a hydro test to failure, because the energy is stored in what amounts to a giant gas spring is thousands of times more than in nearly incompressible water. That is why hydro testing is preferred.
The video of the air tank exploding inside that chamber should make it clear, that that is what we are trying to avoid. Any arguments that are not about avoiding hazards are just hot air.
The chamber door is distorted after the bang, because of the amount of energy released.
If your PCP air tank can enable you to shoot 100 shots at 30 FPE, and the overall efficiency is 50%, then the energy contained in that air is over 6000 FPE (because you do not shoot it down to zero). If all the air in that tank is released abruptly by rupturing the tank wall it has the potential to do a lot of damage. Way more than would happen in a hydro test to failure, because the energy is stored in what amounts to a giant gas spring is thousands of times more than in nearly incompressible water. That is why hydro testing is preferred.
The video of the air tank exploding inside that chamber should make it clear, that that is what we are trying to avoid. Any arguments that are not about avoiding hazards are just hot air.
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The way the marauder tube failed in Lloyds test would not have resulted in an explosion with air, the failure was not catastrophic. In hydro-static tests where they are catastrophic the resulting damage is generally loud, and the damage very evident that the event would be catastrophic, plenty of examples of failed hydro-static tests showing this. The failure observed during the ocean gate vessel's testing was so profound it shook the colleges building and damaged equipment.
Again, I am not the only one holding the opinion that this thin margin is worrisome, yet you're hyper-focusing on me. I don't stand alone, having a tube fail at just 20-30% over stated fill pressure is not okay in my book. If you feel comfortable with those margins so be it, I am not here to change your mind. I am not here to win anything, it's not how this works.
-Matt
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In Lloyd's video the valve retention screws pushed back allowing a small minor gap to where the air would relieve itself so fast that the pressure would drop rapidly, not allowing the valve to push back further. A more catastrophic event would be one where the valve screws failed and the valve then launches itself from the tube much like a projectile down the bore of an airgun.
So yes, building design features that allow the least catastrophic failure in the event of one is most desirable, but those features shouldn't allow failure at only 20-30% over stamped pressure.
-Matt
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Here is a video of a catastrophic type of failure, this would be very unpleasant to be around be it using hydraulic fluid or air.
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The o-ring failure video is closer to the AA failsafe design, in that it does not throw chunks. The video where Lloyed ruptures the tube would be more violent, of air were used; and it failed at 30kPSI, not 10.
I am posting both videos below:
I am posting both videos below:
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I am not opposing controlled design failures, in fact I encourage them... I am merely stating my concern with them being only 20-30% within manufacturers recommend fill pressure..
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OSHA standards apply to employers subject to the Occupational Safety and Health Act of 1970. One needs to know how to read the entire standard, including all of the peculiar OSHA definitions and standard interpretations to properly apply them. The short/easy answer is that it is not applicable to an airgun used for its intended purpose.
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There is no standard for pressure vessels of this size, they aren't held to any that I am aware of. There's also a bunch of literature for ASME and DOT standards in these regards but again, pressure vessels of this size do not apply. Doesn't change my stance nor the many others who feel the same way. The literature I provided is in regard to general safety that I intend to adhere to for airguns in my possession.
-Matt
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Funny you state 50% when the OP's gun failed at way under that. I'd have no problem personally with someone who filled 20% over with for example a marauder.
-Matt
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You made it clear than damage at a 30% overfill was not acceptable. So, I am asking if you would be OK buying a PCP that had been overfilled by 50%. Not once, but every time. Because it could stand 300%.
Or is it just that fact that some over filling can be hidden, and others result in instant obvious failure?
The AA 500 manual states not to fill over the pressure indicated on the cylinder. That the warranty would not cover damage that results. It does not say, don't fill more than so many percent over:
Linked manual from the AAUK site:
S510-XS-FAC-ISS3.pdf
drive.google.com
It doesn't take an intentional overfill to achieve failure here, corrosion, scratches, dents, dings, faulty gauges, and temperature swings from cold fill to a hot car could result in failure.
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Again, faulty gauges (very common in 25-28mm sizes), corrosion (not uncommon in 10-20+ year old tubes), scratches (also not uncommon in 10-20+ year old tubes), and large temperature swings from initial fill (here in Colorado it can go from <30F to 70F+ in the same day, where a car exposed to this heat can easily reach 100F+) are just a few of the potential contributing factors here. It's highly advisable to have a larger margin of error than 20-30% between stamped fill pressure and the pressure at which a controlled failure occurs. To that end, we're both running circles around the same statements, and I have nothing more to add here.
-Matt
-Matt
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That's the unit I'm waiting on. I ordered it about a week ago, but it has to ship from the UK.These come with a lower profile un-threaded stainless steel probe now. Already has a Foster fitting machined into it.
Air Arms Quickfill & Pressure Gauge Units, CNC'ed In England by Lane Regulators. | eBay
This quickfill unit can be installed in to and is compatible with all Air Arms versions Series Listed Below By Lane Regulators - Manufactured in the UK. ane Regulators, Regulator Parts & Kits. Air Arms - Regulators - Spares & Accessories.www.ebay.com
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I'm relatively certain that the last fill did not exceed 250 bar based on two things. One, I had the cut off set at 250 bar and two, I was periodically checking it as it filled and from my observations it was in the neighborhood of 220-230 when it let go. I wasn't peering at the gauge at the time, but I had checked it recently as I was waiting for it to complete its fill and so far the gauge on the compressor has been very close to the gauges on my different airguns.
I believe the damage had started prior to that, as I was experiencing a slow air leak prior to it failing.
One other thing that I wonder about is that when I had the gun apart to install the regulator I attempted a reblue on the tube using a cold blue. I heated the tube in the oven to approximately 175F to see if that would help with the bluing. It was cool enough that I was able to handle it with a rag and rest it on my pant leg while doing the rebluing. I was trying not to do anything that might affect the heat treatment of the tube. I would think that this would be far below any temperature that would affect the strength of the tube, but in light of what occurred, maybe it wasn't.
Once you make any claim on the internet there are those who will understandably doubt your word. If you choose to doubt me, there's nothing I can do to prove otherwise. TBH, I really don't care all that much. I just wanted to let others know what I experienced in case they were considering doing something similar. I know that had I read a similar report that I would not have do so.
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I'll chime in with info specific only to my narrow expertise in regards to metal finishing and heat treating as it applies to airguns/firearms. 175 F will not affect the heat treat of carbon steel. In fact, the factory "hot" blueing bath operates at a temperature of 292 F to 311 F depending on the type/alloy of the steel being blued.
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Thanks. I thought I was keeping it well below any temperature that could affect the temper, but after having it deform like that I started to wonder.
I'm of the opinion that this particular aspect of the S4xx design was fine at the time, but is now a weak point if you abuse it. It seems Air Arms came to a similar conclusion as their new rifles are rated to a higher pressure. Back in the days of non-regulated guns, handpumps and aluminum scuba tanks charging over 200 bar just wasn't very likely to happen and would either make your gun shoot slow or lock up the valve. These were seriously nice shooting guns though and I'd be surprised if large numbers of them don't get retrofitted with regulators and once it's been regulated the gun won't shoot slow or lock up with a big charge of air.
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Thank you for your polite reply.
As the air tube is relatively soft I am sure that you did not soften it by such mild heat. For example, the tempering temperature for 4140 to achieve a hardness of 40 Rockwell C is 400 degrees Celsius. You would need to exceed that temperature to reduce the hardness below 40 RC. I think PCP air tubes are low carbon steel, and that very few manufacturers heat treat them to begin with.
Some home builders use 4130 steel for air tubes, and that typically comes delivered at RC 20, which is twice as strong as mild steel. Anything stronger than that adds too much cost to the typical production airgun.
If you are confident that your o-ring blow out occurred at less than 250 BAR, that means the margin AA have on their system is less than 30%. They really do mean, don't fill over the pressure on the tube. A good data point for the rest of us.
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It's not just overfilling, one could fill at the recommended pressure of 200 bar with the older tubes at 40F and leave their rifle in a hot car and experience the same failure as OP as that itself could raise the pressure to 240 bar, never mind an air tube with a scratch, gouge, dink, any corrosion or other compromises present at that location of the air tube.
Very curious if their new design also includes the exact same design features as OP's older tube.
-Matt
Very curious if their new design also includes the exact same design features as OP's older tube.
-Matt
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You are right, Stubbers; increasing the temperature of the tank from 4 to 40 degrees C, will take it from 200 to 240 BAR.
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Happy to help where I can. I'm a retired firearm gunsmith, and a devoted springer guy. Love my Weihrauch and Diana rifles. However, I'm getting ready to invest in my first PCP, and I've been reading everything I can about the subject, both the positives and negatives, including this thread. It's all interesting to me. I have a lot to learn in regards to PCP's, and their safe use. There's a large base of knowledge here, so, I read.
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