Plastic second stage failures

[Akimbo]

There is an interesting article in the Spring 2017 issue of Alert Diver Magazine: A Free-Flowing Failure

The plastic housing of the second stage failed and caused a freeflow. It isn't clear to me if the plastic housing was exposed to full IP pressure or not. Does anyone know what regulator this is?

Here is a related article that shows how long it takes for various failures to empty a single 80 that appeared in Advanced Diver Magazine:
Life Ending Seconds, 3000 to Zero in 72 Seconds

 

[tech3324]

The yellow 2nd stage pictured is a US Divers octo, I have one. I think any of the USD plastic 2nd's like the SE or SEA series are exactly the same construction. I do inspect them but have not had a failure.

 

[Akimbo]

I don't have an exploded view, is the housing exposed to LP pressure? The article is a little vague.

 

[tech3324]

Here's an exploded view of an SE. I think only the metal inlet fitting is exposed to LP. What do you think?

Why does the pdf not display inline?

 

[Akimbo]

Yeah, it looks that way to me. Thanks.

 

[cerich]

cracks in second stage housing used to be not uncommon, almost every brand had issues along the way, USD, Oceanic, Dacor, HOG and I am sure a few more I cant recall off the top of my head.

In the last 5 years or so virtually every brand has moved to better plastic choices... why it took so long ion some cases I don't know.

It was in fact something I chased very early at HOG. I hated the material our oem used with all the brands they made seconds for, then once I got the material I wanted watched the other brands they made for start to change to the material I choose.. LOL I could get mad about it but in fact I am glad because it really is a better material. Heck I even told some other brands that their material sucks and to use the one I choose, at first they got mad at me, then even the maddest eventually changed over.

 

[Akimbo]

A lot goes into the quality of injection molded parts beyond the material itself, which is also true of metal castings. It is a little surprising to me that the LP (Low Pressure) circuit isn't entirely made from metal parts like all the regulators I'm familiar with. I don't have any reservations over plastic second stage housings. Not many common (inexpensive) injection molding plastics are rated for pure O2.

 

[cerich]

A lot goes into the quality of injection molded parts beyond the material itself, which is also true of metal castings. It is a little surprising to me that the LP (Low Pressure) circuit isn't entirely made from metal parts like all the regulators I'm familiar with. I don't have any reservations over plastic second stage housings. Not many common (inexpensive) injection molding plastics are rated for pure O2.

most seconds are metal where the air passes in, however, the housing still needs to be waterproof, and if it cracks, it literally sucks water with every breath.

Plastics, being what they are, some batches were OK, other batches were a PITA, a very common plastic used by many brands was tough but when cured not well, or additives off or whatever could end up pretty brittle and cracks would start to appear with long term curing (months here) or stress fractures.

The yellow octo in that article was famous among techs for it in the 90's, I saw dozens, maybe hundreds of them with cracks.
I also have experienced entire shipments by the time they arrive have cracks(thus why I said no mas to that type of plastic), and know of other brands that would get a batch of second stage housings that cracked as well.

Other brands historically choose better from the get go or changed in late 80's , others were more stubborn on their choice because when done right they were fine and much lighter. problem was that consistently done right wasn't so consistent.
I want materials that last as long as possible, always.I am ok with a little more weight, it isn't like we don't add lead to sink anyhow. Yeah, it's a travel issue..but I will fall on the durable side of the coin

 

[cerich]

most seconds are metal where the air passes in, however, the housing still needs to be waterproof, and if it cracks, it literally sucks water with every breath.

Plastics, being what they are, some batches were OK, other batches were a PITA, a very common plastic used by many brands was tough but when cured not well, or additives off or whatever could end up pretty brittle and cracks would start to appear with long term curing (months here) or stress fractures.

The yellow octo in that article was famous among techs for it in the 90's, I saw dozens, maybe hundreds of them with cracks.
I also have experienced entire shipments by the time they arrive have cracks(thus why I said no mas to that type of plastic), and know of other brands that would get a batch of second stage housings that cracked as well.

Other brands historically choose better from the get go or changed in late 80's , others were more stubborn on their choice because when done right they were fine and much lighter. problem was that consistently done right wasn't so consistent.
I want materials that last as long as possible, always.I am ok with a little more weight, it isn't like we don't add lead to sink anyhow. Yeah, it's a travel issue..but I will fall on the durable side of the coin

I recall one reg that didn't crack in use, but when you went to service it about 1/3 of the housings would crack, and my shock recently when the latest version of said reg had the same plastic in the same trouble spot, they must like selling cases. (I actually broke a new one when looking at it... to show a engineer the problem, he wasn't that impressed with me)

 

[Akimbo]

however, the housing still needs to be waterproof, and if it cracks, it literally sucks water with every breath.

No debate. The real issue is a housing failure can make the second stage inoperable but shouldn't freeflow. I've had all metal US Divers second stage housings fail and diaphragms split on Poseidons. Dumping gas at a high rate is an unacceptable failure mode.