N/A Why don't PCPs all have safety burst disks?

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Normkel

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Aug 21, 2020
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The only PCP that I recall that has/had a safety burst disk was my Kral Mega Marine. That is a feature that I value highly, but it seems that only a few guns have what seems an obvious safety feature.

Many Kral have them, and a search shows that some: Trimex (never heard of that make), Niksan (never heard of), Reximex, Air Venturi, Pallas (never heard), Kuzey (never heard).

* the "never heard of" comment isn't a shot at these makes, simply illustrating that I haven't even known to consider these for purchase.
 
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Some do, but most don't. The theory is that an oring would give out and not hold pressure if you go too high in the action. Bottles are another matter. Aluminum would go crazy, that's why they are normally, if not all, limited to 230 bar, (there might be a 250 bar, but I've not seen it). Carbon fiber are really strong and they typically would leak with a loud hiss and not go boom.

These things, handled with even a decent modicum of care, are inherently very safe. Manufacturers couldn't handle the liability insurance if they weren't. I used to work in the plastics industry and did some work with HPA cylinders ie CF, and I can tell you that it takes a very high pressure to get them to leak. IIRC breathing air cf cyls have a failure pressure of something like 17,000 psi, or over 1100 bar. That's for a (again going from memory) 7" diameter cf cyl. As cyl diameter goes down, the ability to hold pressure goes up. So a 60mm cf cyl would have an even higher failure pressure, assuming the same thickness dimensions. That "smaller diameter=higher pressure capability" is why in the USA, any cyl under 2" does not require a periodic test, as if properly designed, it can hold a lot of pressure.

That info is from a few years back, so take it with a grain of salt.
 
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Normkel said:
The only PCP that I recall that has/had a safety burst disk was my Kral Mega Marine. That is a feature that I value highly, but it seems that only a few guns have what seems an obvious safety feature.

Many Kral have them, and a search shows that some: Trimex (never heard of that make), Niksan (never heard of), Reximex, Air Venturi, Pallas (never heard), Kuzey (never heard).

* the "never heard of" comment isn't a shot at these makes, simply illustrating that I haven't even known to consider these for purchase.
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I'm leaning into a meme here... No need for a burst disc, 700 orings will let loose first.
 
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Normkel said:
The only PCP that I recall that has/had a safety burst disk was my Kral Mega Marine. That is a feature that I value highly, but it seems that only a few guns have what seems an obvious safety feature.

Many Kral have them, and a search shows that some: Trimex (never heard of that make), Niksan (never heard of), Reximex, Air Venturi, Pallas (never heard), Kuzey (never heard).

* the "never heard of" comment isn't a shot at these makes, simply illustrating that I haven't even known to consider these for purchase.
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Kral, Reximex, Kuzey are all the same ownership and share some parts. That's why you see them with the same style burst disks. Niksan also Turkish Imported by Donnyfl. Pallas is either another subcompany of kral or another Turkish company making the same guns. Trimex appear to be a rebrand of the Niksan for another market of the world.
 
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bchannell said:
Some do, but most don't. The theory is that an oring would give out and not hold pressure if you go too high in the action. Bottles are another matter. Aluminum would go crazy, that's why they are normally, if not all, limited to 230 bar, (there might be a 250 bar, but I've not seen it). Carbon fiber are really strong and they typically would leak with a loud hiss and not go boom.

These things, handled with even a decent modicum of care, are inherently very safe. Manufacturers couldn't handle the liability insurance if they weren't. I used to work in the plastics industry and did some work with HPA cylinders ie CF, and I can tell you that it takes a very high pressure to get them to leak. IIRC breathing air cf cyls have a failure pressure of something like 17,000 psi, or over 1100 bar. That's for a (again going from memory) 7" diameter cf cyl. As cyl diameter goes down, the ability to hold pressure goes up. So a 60mm cf cyl would have an even higher failure pressure, assuming the same thickness dimensions. That "smaller diameter=higher pressure capability" is why in the USA, any cyl under 2" does not require a periodic test, as if properly designed, it can hold a lot of pressure.

That info is from a few years back, so take it with a grain of salt.
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I am a Power Engineer and still retain some memory of pressure vessel dynamics, although it's likely a bucket of salt in my case. ;-)

CF bottles fail in the sense of a large leak, rather than an explosive burst, is my memory. Plastics = magic, so your explanation is informative. I recall the test and burst pressures as being 3x-5x working pressure for some pressure vessels.

It was in the sense of a (hazard) burst, rather than (inconvenient) leakage that I was posing the question.

It is illegal in some jurisdictions to transport a pressurized gas vessel in the passenger compartment of a conveyance, which I feel is more than reasonable.

I was uncomforable and stopped transporting SCBA tanks to the range because I had to have them inside. Perhaps I should be more clear when referencing that as my concern was not with regards to a catastrophic burst, but rather the effects of even a modest rate of venting of 45 minute or 60 minute, 4500 PSI into the vehicle. I feel that retaining control would be a concern.

With regards to an "O" ring acting as a safety release, they are routinely employed for much higher gaseous and liquid sealing. If the "O" ring is to be the safety release, it might seem that substituting an "O" ring of different material or dimension might negate the untility?

I wonder if anyone has queried the designers to determine which "O" ring is the "weak link"?

I'm probably the only one who is learning from this thread.
 
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Normkel said:
Lacking in any artistic talent, no meme will be forthcoming from here, but I hold great hopes that someone may contribute.
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It's thought meme with the contingent of anti pcp or anti cuz pcp brand because oring leaks.

I can tell you that on an fx maverick, if your buddy is pretty beer buzzed and cranks the second reg to 190 bar because supersonic slugs is amusing in the moment,the gun vents on its own and I have to rebuild it for them 😂
 
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Motorhead said:
At such time when SAFETY becomes having a FAILURE :oops: you got much larger design and materials issues to work out !!!
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It's subjective. I'm a fan of the gene pool working itself out, but why don't any of the industrial pneumatic controlled machines I work on have blow off valves on them when a ram could be sent to outer space if things went wrong? I get your point but any gun left in the sun is going to vent, or extrude an oring and still vent.

That said I've done some crazy home brew pcp stuff and paintball stuff over the last 25 years and it's much safer than we would think but is obviously to be respected . I've had burst discs do there job 1 time, other than that they've all been failures from cyclic life or moisture in the air. Well and a co2 one from a friend putting it in hot water to up the pressure in early paintball days.

Safety precautions retain vision, fingers and lives.
 
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Ohhhhh, extruding an o-ring, my Tuxing does that on the filters and I don't get much above 310 bar, which is where the burst disk kicks in. My Raptor has burst disks but they are set really high, never really wanted to test the upper limits of stupidity, been in the gene pool for a bit, for some unknown reason.
 
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On extruding o-rings, while a softer 70-75 duro is indeed softer than say 90 duro. Both can seal at high pressure SO LONG AS .... the tolerance of clearances present don't allow the o-ring material to migrate out of the containment groove being forced to travel within the gap of a poorly sized joint. As In: Od of the male part being within the I.d. of female section too loosely.
* I've seen countless times when taking apart High Pressure PCP's where said o-ring is nearly out of its containment groove and a black smear along side both assembled parts pushed down stream of the pressure source.
Other times when fit is excellent, the o-ring is so square with zero migration into the gap !!!! you would swear it is some sort of new newfangled seal design :rolleyes:

Biggest issue with using 90d where 70 is specified is that 90d has very little stretch or compressablity. Try and stretch a 90d onto a male fittings o-ring groove it either won's stretch that far before breaking, or suffers that once assembled into the female component said o-ring won't compress enough to allow assembly, or hangs up on a shoulder if present. Forcing parts together will many times simply slice the o-ring on it's O.D.

Just a share ....
 
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Motorhead said:
On extruding o-rings, while a softer 70-75 duro is indeed softer than say 90 duro. Both can seal at high pressure SO LONG AS .... the tolerance of clearances present don't allow the o-ring material to migrate out of the containment groove being forced to travel within the gap of a poorly sized joint. As In: Od of the male part being within the I.d. of female section too loosely.
* I've seen countless times when taking apart High Pressure PCP's where said o-ring is nearly out of its containment groove and a black smear along side both assembled parts pushed down stream of the pressure source.
Other times when fit is excellent, the o-ring is so square with zero migration into the gap !!!! you would swear it is some sort of new newfangled seal design :rolleyes:

Biggest issue with using 90d where 70 is specified is that 90d has very little stretch or compressablity. Try and stretch a 90d onto a male fittings o-ring groove it either won's stretch that far before breaking, or suffers that once assembled into the female component said o-ring won't compress enough to allow assembly, or hangs up on a shoulder if present. Forcing parts together will many times simply slice the o-ring on it's O.D.

Just a share ....
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Which is why I boil the darn thing they stretch when hot. They do return to original dimensions when they cool.
 
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Considering how many funky extruded O-rings I’ve replaced over the years, I will freely admit my instincts were that an O-ring is likely to give way in the case of an extreme overpressure condition. However one day I was talking with the lead designer of a reputable PCP manufacturer about hydrotesting. I naively assumed they had to take special measures when testing at extreme pressure to prevent O-rings from giving way. His answer: Nope, just the same 70 durometer O-rings we use in standard production.

The examples of extrusion failure we typically see are the result of more sane pressures acting on the elastomer…but for a long, long time. For short periods of time, the material may be capable of holding vastly higher pressure, and that’s no bueno if the vessel decides to give way first.
 
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I had a pressure failure once when I overcharged my S410. Air Arms did do a pretty good job of engineering a safe failure point into the design. The way the reservoir is designed, it's weakest point is after the threads at the muzzle end so if it fails the thin area mushrooms out and the o-ring is extruded. There was a loud whoosh when it happened, but no bang. A burst disc would have been better though.
 
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