Leshiy 2 explodes

[Glem.Chally]

Compression generates heat. That's why our cylinders and tanks are warm after filling.

Fire piston - Wikipedia

en.m.wikipedia.org

Fair enough, but the guy I'm quoting is asking what the source of ignition is in a cylinder and how could it blow? Essentially, I was just saying that it can ignite without heat. Unless I'm mistaken on that? I've been wrong before haha.

Edit. I should have said source of ignition not heat in my first comment, my bad.

 

[sb327]

For combustion, 3 things are needed.
Heat
Oxygen
Fuel

How much heat? Stubbers eluded to the heat during filling. He is correct and he also quantified by saying it would need to be a fuel with a low ignition point. Although warm, I do not think our compressors can fill fast enough to create the heat needed. ETA: in the reservoir, obviously it can create the heat needed in the compressor’s cylinder

From a tank? Yep, heat is created, but again, the fill rate is limited (especially in a Leshiy2 considering the type of check valve). Nothing like a diesel engine for sure.

A springer diesels (combusts) due to the rate of compression creating enough heat.

Dave

 

[Motorhead]

Just a thought exercise for all those thinking it could be oil (alone) that caused this. Remember, a drop in pressure (shooting) creates a cooling effect.

Dave

In containment yes it does.
A HP leak contacting atmosphere pressure compresses those molecules in close proximity creating localized heat .... best I understand the physics going on.

But then again a laymen in such physics

 

[stoutblock]

I am convinced a pristine sample is more than safe. Yet we have a catastrophic failure of a production article in service that should be understood. A true understanding requires it to be duplicated. I have not heard the results of the lab tests? Material, induced damage (impact), corrosion, machining flaw, fatigue etc?

 

[jarmstrong]

any history of diesel ignition causing equipment damage or operator injury in pcp shooting or bottle or gun tank being filled,
damage or injury?
do not care it someone managed to get a little diesel in a big bore high flow, in the transfer port area, that did 'not' create a damage problem. I am looking for real world negative results, not theories.
Please post or link them here, I had enough fear p orn, chicken little,,, "the sky is falling". I would to see evidence, please.
I am not trying to start an argument, I am open to proof.

I do not think this is the source of the Leshiy failure.

 

[sb327]

That was kind of my point with my thought exercise. If pcp’s diesel ignited AND failed, I think it would be prevalent.

The whole subject is kind of the elephant in the room when it seems I read almost daily someone saying DO NOT GET OIL IN A PCP…SILICONE ONLY. My question to myself is always why? And if it can combust, how?

I’m really curious to see some evidence.

Dave

 

[subscriber]

Overly rapid filling of a low capacity airtank can raise the temperature inside high enough to do nasty things. The link below is about an HPA filter being pressurized very rapidly because its exit valve was closed. This rapid compression of the air in the filter tube resulted in the white filter material inside being scorched brown, and potentially igniting fully due to what amounted to adiabatic compression. Essentially, like a fire piston would ignite solid tinder. Except, if a large enough volume of solid fuel was lit in excess air already at several thousand PSI, this could potentially blow up the container.

Presumably, flammable oil might be ignited under similar circumstances; but, while an oil film may not have the surface area of air filter fiber material, high enough temperatures could cause oil to flash boil, then the vapor to ignite:

How hot does the air in a PCP get? Probably Hotter than you think. - Airguns & Guns Forum

How hot does the air in a PCP get? Probably Hotter than you think., Air guns, Airgun Forum

www.gatewaytoairguns.org

 

[Stubbers]

I uhm don't want to admit to this but....

I had a hand pump causing issues once, I was angry at said pump and forcing that pump up and down like a hungry gorilla, what resulted was every o-ring inside the gun being ruined due to heat, and I scorched the cotton filter inside the hand pump, literally burned to a crisp.

You don't even need to rapidly fill a pcp reservoir to bugger things up.

I strongly do not believe this incident of failure was caused by similar, but heat can certainly be introduced into an airgun via rapid filling or...a failed pump filling.

-Matt

 

[CsakEn]

Cool videos about the fire piston thanks for that, you see what I meant. If there is a fuel oxidant mixture it will burn.
anything liquid can and condense and collect. If there is too much oil in the head may not all burn in the compressors head it will get past it…Did I see some liquid level collection pattern on the bottom of the cylinder or was that some anodizing imperfection?

I am a scuba diver enriched mix cylinders have green special o ring material not even the standard black o ring stuff Like in PCP. But green o rings are expensive you know...and strictly no lubricant. Maybe the cylinder was taken apart lubed up with the wrong lube. petroleum based lubes are more common than our silicon based special type. Remember that.

Or he just used oxygen tank from a hospital that would explain it all. Mystery solved.


looking at different tooling shapes maybe Ed wanted to give you more shots per fill by drilling deeper

 

[subscriber]

The blown Leshiy tube does not have soot on it. Unless such was cleaned off, this bang was probably not caused by combustion. But overpressure on top of a marginal design is still on the table. The question was can one have dieseling inside a PCP air tan?. The answer is "yes" of fast filling, but "no" on firing - assuming combustible fluid or dust is present in large enough quantities to add significant heat.

Fire pistons use dry fibrous material to generate embers. I have not seen anyone use oil in a fire piston, except to demonstrate dieseling. This is because the oil does not have the properties to make a useful ember. If you manage to light it via rapid compression, the flame goes out rapidly, even if liquid oil remains

At 16 minutes and 24 seconds into the video below, dieseling is demonstrated with what amounts to a fire piston.

The rest of that video is pretty interesting and entertaining too.

 

[JimD]

Most gases including the oxygen and nitrogen in the air cool as they expand due to the Joule Thompson effect as already mentioned. But oil doesn't cool, it heats up. It seemed like the manufacturer's initial reaction was a moisture issue. Could there have been a moisture issue that also involved getting compressor oil into the tank? A shot happens to have just the right amount of oil in the air going through the valve and it diesels?

My guess is whatever happened is pretty unlikely. I don't know about the design margins in the Leshy 2, I read at least several of those posts but I am still not sure if I agree the margins are lower than normal. But there has to be at least hundreds if not thousands of Leshy 2s being used and only one incident like this reported? That suggests to me whatever happened is an unusual combination of things.

 

[subscriber]

Jim,

Somehow I think if combustible oil is used i a compressor, that compressor would be damaged by dieseling, long before any PCP downstream chokes on oil residue. Compressor manufacturers are careful to specify "compressor oil". If you used engine oil in your Yong Heng it would not last very long...

I have never heard of oil heating up when the pressure is dropped suddenly. Just because I have not heard of something does not mean it does not exist. Perhaps any molecular agitation will heat oil. On the other hand, diesel engines work by compression ignition. Yes, there is flame on expansion, but it was initiated on compression.

Back to the Leshiy; doesn't it have two air tubes? If one had conditions that would provoke dieseling, what about the other? Both would contain oil residue (if that were the problem), and even if the second tube was stronger, the bang in the first would raise the system pressure further and set off the second one. If the second tube is totally undamaged, then the exploded tube was defective in design, manufacture or material. Making one tube stronger and the other weaker deliberately in terms of pressure holding capability would be like making a chain with half the links weaker to save weight...

One could ask where the fill port is on the Leshiy? Is it possible to fill it so fast that the tube temperature can get high enough to anneal the material? I would think that would take some doing, and that it would melt the synthetic material cheek rest. Or at least make it stink.

Or is this a case of a sharp corner provoking material fatigue from habitual overfilling "for a few more shots", then a crack unzipping when it had had enough.

Corrosion from moisture seems more likely than dieseling from oil. Although anodized aluminum is usually a pretty good protective layer. Anodizing is brittle, so it may actually reduce fatigue resistance in a corner with a less than ideal geometry. If the anodizing crack, moisture can get at the base metal and corrosion can help to degrade the area of the tube that can least afford it.

Adding a simple burst disc to the system would help substantial over filling. But using a burst disc that fails at 100 PSI over rated will pressure will itself fail after a less than ideal number of fill cycles. So it is customary to use burst disks that are perhaps 1000 PSI above the rated fill pressure - and well within the margin of safety - because you are not supposed to fill that high, if you read the manual.

Does the Leshiy have a burst disk near the fill port? If not, it seems to need one...

 

[subscriber]

In theory, a PCP could diesel in the air space behind the projectile, before the projectile starts moving, and before that space expands. The high pressure air rushing in is going to compress the ambient air already behind the projectile, and heat that space for an instant before the projectile has had time to get moving. As soon as the projectile moves, the space behind it expands and then after a very short time, the TP (and flow path) acts as a flow restriction. Both of these factors cool the air below ambient temperature; thus cancelling any heating that occurred as the poppet opened. Now, the air rushing past the partially open poppet probably causes enough pressure drop over the valve to cool the air in the "heating period" I am suggesting might exist behind the stationary projectile that is yet to overcome its stiction in the chamber. Followed by inertia.

Has anyone had a PCP shoot faster and louder while generating a burnt oil smell (else it could just be the poppet valve sticking open occasionally) ? I have not heard of PCPs dieseling on "firing". If you could provoke a PCP to diesel on firing, it would seem to occur in the barrel, rather than in the air tank or plenum, where the air expands and thus cools on firing. The barrel is strong because it has only a small diameter hole down the middle, so barrels are typically not damaged by dieseling in springers, for example.

Yes, PCP barrel walls are often thinner, but just go and look at the pressure rating for thin walled hydraulic lines, made from annealed steel so that they can be formed by bending to fit a given application. Or look at the unsupported rim thickness of a brass .22 rimfire case. Small tubes don't need thick walls to stand high pressures.

It is the comparatively large bore of a PCP air tank that makes it so fragile, and its large internal volume that stores so much energy, that makes it pop "so easily", and make such a mess when it lets go.

 

[Stubbers]

I have had smoke from the muzzle of my pcp barrel, to what the cause was? Idk, I'll never forget it nor has it been a common occurence, but it certainly wasn't the plume of adiabatic air exhausting the muzzle, it was a slow wisp of smoke that did have a smell to it.

-Matt

 

[subscriber]

Thanks for the data point, Matt.

 

[Cloudrider]

I have had smoke from the muzzle of my pcp barrel, to what the cause was? Idk, I'll never forget it nor has it been a common occurence, but it certainly wasn't the plume of adiabatic air exhausting the muzzle, it was a slow wisp of smoke that did have a smell to it.

-Matt

I would guess that be vapor from projectile lubricant...

 

[Stubbers]

I would guess that be vapor from projectile lubricant...

Probably spot on! Although like I said I don't think its common so must have been a specific condition with the valve that contributed? I don't recall if it was my balanced valve or conventional valve that it occurred on. Thanks for commenting.

-Matt

 

[subscriber]

There is a difference between heating lube hot enough to evaporate, and hot enough to start an exothermic reaction. Oil vapor and burnt oil vapor don't smell the same. Ditto for wax vapor and burnt wax vapor.

 

[JimD]

I think the point about compressor oil being resistant to ignition is a good one. But it is not immune. The flash point is just higher. I also kind of doubt that the expansion of the air in the plenum would cause oil to get hot enough to ignite. It was Wikipedia but when I reviewed the theory of gas cooling the article mentioned oil heating up. No idea how much. It is hard to believe it could get hotter in the gun than it does in the compressor. But if it happens on expansion the air would not necessarily be in the barrel yet and the regulator might be open. The regulator would seem to need to be open for the resultant pressure spike to affect the air storage chamber. I doubt this is the cause, just seems like a remote possibility if nothing else checks out.

I offered to swap another scope onto my son's inexpensive break barrel - a Crosman nitro piston - and whatever oil he used on it dieseled on the first shot. Unmistakable sound but some of that could have been the speed. I think it was supersonic. Sharp crack like a powder burner. If a PCP dieseled in the barrel I would expect it to be unmistakable too. If it happened inside the gun, it would seem like it would probably not be subtle either. But it seems far fetched it could happen inside the gun. It would require the temperature increase from expansion to exceed the flash point for the lubricant.

 

[Sicumj]

There is a lot of speculation. So again this looks like a drop or explosion. Unless you analyst the metal for traces of hydrocarbons you cannot rule out a petroleum ignition. Which I doubt. My guess is we will always be guessing what happened here. If you cannot recreate the fault, you have not proved the cause.