Getting my First Reg - Need Advice

[buddhasummer]

He mentioned 2 years.

 

[Darghu]

I read wrong my bad.

 

[george_austin]

I was in contact with Miflex at the time, and there was much suggestion that hose failures may have been due to improper maintenence.

I confirmed this wasn't the case... In 25 years diving, I'm unaware of anyone ever cleaning hoses internally using detergents.

I informed Miflex about the issue of polymorphic crystallization, but didn't get a reply on that matter.

When DAN SA took up the investigation, the issue of polymorphic crystallization was somewhat substantiated - and has featured in their warnings.

I'm unaware if/when Miflex accepted that as the issue and/or took corrective actions.

Thank you for this. Probably the most important thread I've read on this board - and the most interesting and eye opening info.

 

[Darghu]

So since 2015 Miflex have not said a word about this issue ?
By any chance did you try specific Miflex hoses to see if 2 y after issues are still here ?

 

[Bierstadt]

The failure mentioned specifically to nylon braided hoses occurs with the inner layer of the hose.

It was first reported on my blog (see below) and was then taken up by DAN SA for investigation and study.

Nylon-Braided Regulator Hose Diving Emergency

Since publishing that report (which was disseminated widely on social media), I received numerous communications from divers / centres across the globe who, upon close inspection, found the same issue. The issue reached the attention of DAN, who instigated a study... which came to the same conclusions as I did (on my blog) about the need for close inspection and the need to attribute a lifespan to these hoses (2 years), regardless of use.

The root cause of the failure is Polymorphic Crystallization of the inner layer. This is a chemical degradation of plastics caused by temperature variation on the hose over time. The material becomes solid, then brittle and then crumbles.

View attachment 417108

You can't avoid temperature variation on the hoses when diving. So, it's not specific to one region or environment. Hoses tend to be stored in warmer temperatures, whether in a heated house (in cold climate) or room temperature (in the tropics). The hose is then cooled when you enter water and compressed air travels along it.

The issue specific to nylon braided hoses is that the degradation of the inner layer is effectively concealed by reinforced middle and outer hose layers. This allows the inner layer to completely crystallise, without obvious external sign, and restrict gas flow through the hose.

In the incident I observed, all the regulator hoses (2x IP reg hoses and 1x LP hose) had been bought as a batch, and all three had failed simultaneously. No failure was apparent at the surface or during initial descent, but gas flow ceased once 2.8ata was exceeded. It required an emergency gas donation (from myself), or it could easily have been a fatal incident

In contrast, rubber (2-layer) hoses would conspicuously bulge, and fail cursory inspection, as soon as any compromise to the inner layer occurred. Nylon braided hoses do not - they are engineered to 'not fail' if the inner layer is compromised. Miflex market the hoses based on this premise.

View attachment 417109

The reason why this failure is particularly insidious is because the nylon braided hose will still appear flawless on external inspection... and the restriction of gas flow may not be evident at surface breathing pressure. Gas supply may only become compromised as gas density increases at depth; as was the case in the incident I observed.

This isn't about 'cheap' hoses.... it's primarily about the higher quality hoses. These high quality hoses are the ones whose middle and outer layer unwittingly conceal the breakdown of the inner layer.

More photos of the same effect that were collated by DAN:
View attachment 417111

From DAN:

"It would be premature to speculate that this deterioration is limited to braided hoses. Previously, hoses comprised a rubber inner hose, a single braid layer for reinforcement and finally a rubber outer sealing layer. Today the rubber inner hose is sometimes replaced with a polyurethane or nylon hose (referred to as thermoplastic). The middle or reinforcing layer is a polymer-filament braid, and the outer layer is either a second braid — which has the advantage of indicating when the inner hose has a leak — or a polyurethane or synthetic-rubber sealing layer.

Newer second-stage hoses with a thermoplastic inner layer may be vulnerable to degradation. This risk does not apply to internal layers of synthetic rubber, which appear to be impervious to this phenomenon. DAN Research would normally wish to conduct more in-depth analysis with a wider sample of defective hoses, but because this is a potential hazard to regulator function we prefer to err on the side of caution and report this phenomenon now." - excerpt from DAN Alert "Invisible Crystals"

Again, novice question here, but do rubber hoses have 2 or 3 layers? If a hose is made with a rubber inner and outer layer I can certainly imagine it bulging if the inner fails... but if it also has a middle braid layer, I don't see how it would. @DevonDiver thoughts on that?

 

[DevonDiver]

@Bierstadt

The problem of polymorphic crystallization isn't limited to nylon braided hoses.

However, the problem of polymorphic crystallization causing degradation that leads to hose blockage IS limited to nylon braided hoses... particularly the high quality 3-layer ones.

This is because the middle layer in these hoses is designed to guard against failure of the inner layer. It does it's job... too well... and disguises inner layer degradation until it becomes catastrophic.

Sure, the hose won't 'burst', but it can block.... leading to sudden and non-rectifiable gas supply failure.

In contrast, a rubber hose will instantly 'bulge' if there's the slightest failure of the inner layer. That's diagnosable pre-dive. You'd change that hose long before you got on the water with it.

As far as I'm aware, only nylon braided hoses have 3 layers: an inner layer, a reinforcing middle layer and a protective weaved outer layer. Rubber hoses I've seen only have 2 layers...an inner layer and outer rubber layer.

 

[Bierstadt]

@Bierstadt

The problem of polymorphic crystallization isn't limited to nylon braided hoses.

However, the problem of polymorphic crystallization causing degradation that leads to hose blockage IS limited to nylon braided hoses... particularly the high quality 3-layer ones.

This is because the middle layer in these hoses is designed to guard against failure of the inner layer. It does it's job... too well... and disguises inner layer degradation until it becomes catastrophic.

Sure, the hose won't 'burst', but it can block.... leading to sudden and non-rectifiable gas supply failure.

In contrast, a rubber hose will instantly 'bulge' if there's the slightest failure of the inner layer. That's diagnosable pre-dive. You'd change that hose long before you got on the water with it.

As far as I'm aware, only nylon braided hoses have 3 layers: an inner layer, a reinforcing middle layer and a protective weaved outer layer. Rubber hoses I've seen only have 2 layers...an inner layer and outer rubber layer.

Thanks. That makes sense. However, the DAN alert claims that rubber hoses can or do have a middle layer as well. If they do not - as per @DevonDiver 's experience - then all well and good - the bulge inspection approach works fine. If, however, there are some rubber hoses that do possess a middle reinforcing layer, then it would be possible for a diver to have a false sense of security with their hose (thinking any inner hose failure will result in bulging). It would be really nice to know what is in our hoses. Do we have any hose manufacturers on the Board? @cerich , can you speak to this question?

 

[cerich]

Thanks. That makes sense. However, the DAN alert claims that rubber hoses can or do have a middle layer as well. If they do not - as per @DevonDiver 's experience - then all well and good - the bulge inspection approach works fine. If, however, there are some rubber hoses that do possess a middle reinforcing layer, then it would be possible for a diver to have a false sense of security with their hose (thinking any inner hose failure will result in bulging). It would be really nice to know what is in our hoses. Do we have any hose manufacturers on the Board? @cerich , can you speak to this question?

even many of the "rubber" hoses on the market, are in fact a type of plastic, not rubber. Rubber hoses are getting more rare

 

[tbone1004]

even many of the "rubber" hoses on the market, are in fact a type of plastic, not rubber. Rubber hoses are getting more rare

are the Deep6 hoses true rubber?

 

[cerich]

are the Deep6 hoses true rubber?

a plastic