Flyng Dragon PCP Air Tube Failure

[stalwart]

I am looking for a XS60 receiver that I can use for a jig. If anyone now wants to dump one let me know. If you want to saw the top only so it won't fire I am fine with that also.

So, what's the plan?

[moorepower]

PMed.

[CptMoonlight]

The bottle had to be put on at some point. Could the bottle have been cross threaded during the build? I suppose there are several possibilities, however, there has to be a solution. Hopefully this is an isolated incident and no one will be hurt. Regardless, the solution needs to be found and if it's a design issue, certainly fixed. If this all comes down to one act of carelessness on the behalf of one person, hopefully that person is no longer working on air guns or has anything to do with them whatsoever.

[tehsquirrel]

I dunno I may be biased some but I call BS. 

So the dude filled it to EXACTLY 1450 right before...  Sure.  Nobody ever says they fill their gun to 1450 unless they want YOU to know "dang" sure they didn't 'overfill' it.  All we know is that this happened in the summer in some guy's vehicle while it was banging around in one of those thin fabric cases. 

You see that damage and you've all seen what 1500 psi is capable of.  Could that have been caused by 1500 psi?  It's certainly possible but I don't think its probable. 

I'm willing to accept all the hate and discontent that this will generate but please understand that there is more going on here just based on the descriptions. 

[moorepower]

It had to have blown straight out without deforming the tube, which kind of leads you to think the thread engagement too shallow to hold pressure.

[moorepower]

I dunno I may be biased some but I call BS. 

So the dude filled it to EXACTLY 1450 right before...  Sure.  Nobody ever says they fill their gun to 1450 unless they want YOU to know "dang" sure they didn't 'overfill' it.  All we know is that this happened in the summer in some guy's vehicle while it was banging around in one of those thin fabric cases. 

You see that damage and you've all seen what 1500 psi is capable of.  Could that have been caused by 1500 psi?  It's certainly possible but I don't think its probable. 

I'm willing to accept all the hate and discontent that this will generate but please understand that there is more going on here just based on the descriptions.

Really, who doesn't know what psi fill they JUST used. If you do a little reading on the forum, there are quite a few guys that fill these to 2kpsi., which by the way, I would hope this would make them reconsider.

[BigTinBoat]

I have received some info from the owner of the gun.... He won the gun a couple years ago at the GTA shoot, and has never used it, so the gun is new, and he has never had it apart.... He took it to Douglas' to shoot a short Chrony string, shot 3 shots, refilled it to 1450 psi and put it in the case and then in the truck and it went bang and the air tube nearly hit his wife in the head as it departed the scene....

I understand the owner would not want to be the one at fault for say overfiling, but the above just does not make total sense to me.

Who takes a gun they have never used, loads it into the car, along with the wife, and drives to a neighbors house to shoot the gun just 3 times (unless something happened to it)? And then fill the gun, to 1450psi (which I'm sure would have taken just a blip of air, right? Would 3 shots have even taken the pressure down 100psi), and drive back home? Not me. I mean why just 3 shots?

[rsterne]

The thread depth an XS-60c / FD-PCP is over 3/4".... Even in soft aluminum, a third of that depth should be overkill for strength.... If the threads were engaged to full thread form height, and since the aluminum isn't as strong as the steel, if the tube pulled out you would expect the threads in the receiver to be missing / torn / severely damaged.... We will have to await better pics of the right inside to determine that.... Finding the tube would tell us exactly what happened, I sure hope that occurs....

Soooooooooooooo.... here come all the conspiracy theories.... and the end of this thread, for it will shortly be locked or end up in the Non-Productive Gate.... 

Bob

[Sfttailrdr46]

 Dave and DEz have both said they want to hold off on any final word until all the facts are in. All I ask as one of the Moderators for the PCP Gate is to not rush to judgement on either case, Mike M at Flying Dragons has stated to DEz that he wants to know what caused the failure more than anyone. Please refrain from speculation or blame placing and lets let the facts speak for themselves 

[ezman604]

I really will plead that folks refrain from all of the conspiracy theory stuff. All attempts are being made by all parties concerned to find out EXACTLY what happened in this case. This thread will NOT find it's way to the NP Gate or deleted. It is needed information and serves as a reminder to all that play with HPA to never get complacent. Use care at ALL times!!!!
Anything can happen to ANY airgun, there is always a possibility of something unusual happening, as in this case. Please keep the conjecture out of this thread and let's stick to the KNOWN facts. As the airgun gets closer examination by Mike, we will hopefully get an answer.
This thread will stay intact and may even become a sticky if necessary. We take safety issues seriously!!!!

[moorepower]

Did anyone else notice the barrel band did not even move?

[ezman604]

Yes...several including Mike. Again, he needs the reservoir if possible to see EXACTLY how to reconstruct the events.

[avator]

Dave and DEz have both said they want to hold off on any final word until all the facts are in. All I ask as one of the Moderators for the PCP Gate is to not rush to judgement on either case, Mike M at Flying Dragons has stated to DEz that he wants to know what caused the failure more than anyone. Please refrain from speculation or blame placing and lets let the facts speak for themselves 

I agree. Locking this thread would be a huge diservice to those of us who own these guns, and there are quite a few of us. I would hope that we can all act as the grown men and women that we are and let the facts tell the story. Especially those that don't own the guns.

[Paul68]

The thread depth an XS-60c / FD-PCP is over 3/4".... Even in soft aluminum, a third of that depth should be overkill for strength.... If the threads were engaged to full thread form height, and since the aluminum isn't as strong as the steel, if the tube pulled out you would expect the threads in the receiver to be missing / torn / severely damaged.... We will have to await better pics of the right inside to determine that.... Finding the tube would tell us exactly what happened, I sure hope that occurs....

Soooooooooooooo.... here come all the conspiracy theories.... and the end of this thread, for it will shortly be locked or end up in the Non-Productive Gate.... 

Bob

My thoughts exactly Bob. Even without full engagement, I would think there would be very clear thread damage. The barrel band remaining intact is certainly weird. I too would love to have that tube found and some good close ups of the both the tube threads and receiver threads posted.

I am beginning to wonder if that tube was fully engaged within the receiver. It LOOKS like it would have to have been threaded on only a quarter of the way at the most to come out like that.  Right now, that's the only way I can see a tube blowing out this way without damaging the threads.

[rsterne]

I have been extremely careful to try and present only the facts that have been given to me, and to try and analyze those logically to the best of my ability.... If indeed the threads did pull apart, it would have been about the least likely mode of failure that could be expected.... I only have a sample of one to base my opinions on (my son's FD-PCP), and although the threads are a bit loose, I have every confidence this would not happen to it.... However, there are reports of much looser samples circulating, even in the XS-60c which the FD-PCP is based on.... That may be part of the story, I hope we eventually get to the bottom of it....

Calculations of thread strength are based on the assumption of a proper overlap and fit between the male and female parts.... This insures a shear plane of very nearly 50% of the material threaded together.... The shear plane is the pitch diameter (roughly the mid-point between inner and outer diameters) times PI, times the length of thread engagement, divided by two, because half the area in shear is in each part, male and female.... The weaker material in shear should fail first, in this case the aluminum receiver instead of the steel tube.... It the threads are not fully engaged, because the female threads are cut too deep (too large an ID), or the thread on the tube too deep (too small an OD), or both, then only the tops of the triangular threads are touching instead of the full face of the thread.... Think of a pyramid, with an inverted pyramid pressing to the side of it.... Now slide the inverted pyramid up, and draw a line through the mid point of the overlap.... The area providing the strength is reduced.... Since the strength of the material is the area in shear times the shear strength of the material, it is now weaker.... Eventually, the weaker material will fail....

Explaining this failure (and assuming the threads pulling out is what we are dealing with, still undetermined but it seems likely) is difficult.... It is possible that the tube was only threaded in a thread or two, although you would expect to see the last thread in the receiver missing in that case.... However, considering that the seal between the tube and the receiver is located 3/4" inside the receiver, where the end of the tube compresses a square-section O-ring against a shoulder, it would be very difficult to get it to seal at all if the tube were only threaded in a turn or two.... The air should have literally poured out nearly as fast as you put it in.... I would point out that even a few threads, properly engaged, should be plently for strength.... even with a soft aluminum receiver.... Finding the missing tube would certainly help a lot....

Bob

[Paul68]

WHich is why I simply can't get an understanding of this failure. If not in fully, no decent seal. If in fully, thread damage should be very obvious...


 

[Tomg]

So the tube left in one piece (nothing remains in the breech) Finding the tube will reveal details, however you would expect the threads on the steel counterpart to have even less damage than the receiver (aluminum) being the weaker part.
I have seen separation of two parts where there was barely any damage to the threads on both parts (pressure was in the 1200psi realm). I was shocked to find no sheared threads, and could only conclude that the outside part expanded to the point of letting go of the inserted part.

[BigTinBoat]

... Since the tube is 7/8" OD, at 1450 psi the end force is about 870 lbs.... That is all I know for now, if I see any more photos of the threads in the receiver I will share that information....

Bob

Bob,

Based on the shape of the tube, the approx weight of the tube and using the 870lbs of force can you "estimate" the max distance the tube could have flown giving an "optimum" angle and discounting the unknown resistance of tearing thru the gun case?

[michaelthomas]

Even very experienced people can make mistakes when filling.....so you can never really rule out that sort of thing.  I saw a very experienced shooter dump 4500psi into one of my guns.  He was borrowing someones tank because his was too low.  It had a fill setup that he wasn't used to.  It can happen.

I'm editing this to say that I'm not suggesting that this may have been the case.....just mentioning it.

Mike

[PakProtector]

... Since the tube is 7/8" OD, at 1450 psi the end force is about 870 lbs.... That is all I know for now, if I see any more photos of the threads in the receiver I will share that information....

Bob

Bob,

Based on the shape of the tube, the approx weight of the tube and using the 870lbs of force can you "estimate" the max distance the tube could have flown giving an "optimum" angle and discounting the unknown resistance of tearing thru the gun case?

I don't think so...but I will invite any and all ov youse out to look. As has been mentined, finding it will be very useful, and the downrange cone is poorly defined, and very large in area. Some of it underwater( SCUBA folks welcome, and we won't drain your tanks for filling PCP's either ). the tube is also stick-sized, and not coloured to stand out....though I doubt we'd find it even if it were orange.
cheers,
Douglas