LP hose fitting failure.

[Richard Mason]

Had a bit of an alarming moment yesterday, just before setting out in the car for my scallop dive.

As some may know, I have a fairly flamboyant drysuit which I’ve had for about 8 yrs now. In the past 12 months, I’ve replaced a neck seal, fitted a shoulder dump, repaired and re-repaired a puncture and since Xmas, covered the boots, which had multiple leaks, in aquaseal and last week replaced a cuff seal.

On Sunday, the zip jammed shut in 28ºC heat, although this eventually came good and I think, although I’m not sure that I’ve fixed that problem…for the time being.

The last few dives which have all been shallow, short duration stuff (10-15 mins at 10-12M), either on scallop surveys for the State DPIW, or this last weekend, returning to catch the bu99ers.I’ve noticed a slow leak from the second stage of my Aqualung Legend, at the drysuit d/f hose outlet.

I assumed this was perhaps a dodgy o-ring and after putting it off for various reasons (complacency and always something better to do, like eating, drinking & sleeping), I finally decided to check it over yesterday morning before returning to the scallop beds for a quick dip.

Anyway, off came the d/s inflator hose, I had a look at the o-ring but could discern nothing amiss but changed it anyway; screwed it back in, gently tightened it with a spanner and the threaded male fitting just sheared off inside the LP outlet. I’d used the spanner gentle as could be and I just felt it give. Shortly after this, my dive buddies (Pink Panther of YD and Bruno) arrived, to find me hurriedly changing to one of my other regulators (an Omega – an excellent piece of kit).

I’d assumed that I’d need to get the sheared male fitting removed by my LDS (it’s soft brass so I didn’t want to risk using an extractor) but Bruno, a retired motor mechanic took one look, grasped the protruding sheared off bit between thumb and forefinger and removed it using finger pressure alone, so it certainly wasn’t in too tightly, meaning I hadn’t used excessive force on the spanner. It also means, that this part was within a beesdick of breaking off and it could as easily have happened during a dive, as in my garage.

Closely examining the sheared off faces of the house and the male fitting, it looks like this has been going west for a while, there’s obvious oxidation of much of the face, with only a little bit of shiny brass, (the bit that finally broke) evident. This was obviously the source of air bubble leakage, so it was a progressive problem.

Pretty scarey stuff, if this had gone during a deeper dive, I’d have been in deep do-dos (although I always carry a pony on anything beyond 10-15M, so perhaps not).

What had caused it? Well, I’ve had this hose (with the d/s) for 8 years now and during that time, it’s lived on at least 6 different regulators and gone through 8 annual services, involving removal & replacement – I can only surmise that the strain of being removed and replaced, perhaps being a little over-tightened by myself and/or others could have fatigued the part, which is only relatively soft brass, leading to it’s failure. It was only serviced 6 months ago too.

Lessons I take home from this?

1. If you have a leak, check it out, if it’s not simply a misaligned O-ring, consider leakage through a crack in the fitting.

2. Don’t over-tighten hoses.

3. Be aware that hoses and fittings carry a real risk of failure.

4. I definitely need a new drysuit.

As for the scallop dive, well another 50 molluscs died a horrible death last night, being eviscerated from their shells with a sharp knife. I was able to borrow a wetsuit for the dive but I have to say it wasn’t a pretty sight; my trim and buoyancy control were ratshit, I hit the bottom with a crash (I had turret shell fragments inside my fin foot pockets to prove it), I was all over the place, it was a horrible dive, I used twice as much air as usual. I think the sensation of water flooding in via every orifice was a bit off-putting too, although in a 7mm hood attached wettie, with farmer johns etc, in 17ºC water, I was actually uncomfortably warm during the dive.

[simon varley]

Rich,

when you tighten the fitting the o-ring compresses into the shoulder and the force is transferred axially. As soon as the threads sheared off there was nothing for the o-ring to press against and the axial force was lost. That's why your mate could remove the stub by hand.

I'm not saying you overtightened it - it doesn't sound so by your description - but you can't infer anything just from the fact it was easily removable.

It does seem a very odd sort of failure. I don't suppose you could post a picture of the failed surface. You can tell a lot from the shape/colour of the fracture face. (well, I can't obviously, but I'm sure someone here can)

[Richard Mason]

Originally Posted by simon varley

Rich,

when you tighten the fitting the o-ring compresses into the shoulder and the force is transferred axially. As soon as the threads sheared off there was nothing for the o-ring to press against and the axial force was lost. That's why your mate could remove the stub by hand.

I'm not saying you overtightened it - it doesn't sound so by your description - but you can't infer anything just from the fact it was easily removable.

It does seem a very odd sort of failure. I don't suppose you could post a picture of the failed surface. You can tell a lot from the shape/colour of the fracture face. (well, I can't obviously, but I'm sure someone here can)

Yes, I'll do that when I get home.

[Jay_Benson]

A photo would be good - but make the failure surface fill the frame. You could benefit from my professional opinion.

Anyway work want to benefit from it right now so its back of your head time.

Look forward to the photo.

[the_negligent_snail]

Originally Posted by simon varley

Rich,

when you tighten the fitting the o-ring compresses into the shoulder and the force is transferred axially. As soon as the threads sheared off there was nothing for the o-ring to press against and the axial force was lost. That's why your mate could remove the stub by hand.

Had exactly the same problem wiht a Cylinder Head stud in a old lancia I was restoring. Bu**er snapped well before the torque setting and the remains were in the cylinder block so could not get anything to grip on it. Phoned round some engineering firms for "Spark erasure" quotes and put off by the amount tried to tap it out with a shap punch (trying to turn it with each tap).

It came out as though it was fixed in butter - no problems at all!

[Richard Mason]

Originally Posted by Jay_Benson

A photo would be good - but make the failure surface fill the frame. You could benefit from my professional opinion.

Anyway work want to benefit from it right now so its back of your head time.

Look forward to the photo.

This is about the best I can do.

[Woz]

Was it leaking from there at all?

[Richard Mason]

Originally Posted by Woz

Was it leaking from there at all?

Yep, I reckon it must have been, the tarnished condition of the sheared faces seems to indicate that it was cracked for a while.

[Richard Mason]

Just one last question for those who know.

I've been discussing this occurence with some of the divers down here and more than one has commented about "cheap Chinese kit". Now the hose concerned is an Apeks, it came with the suit, which is a Protec, admittedly now 8 years old (so it's hardly surprising, something had to give sooner or later).

But does anyone know where Apeks would source things like hoses?