Scubapro SPG Failure

[Mike Walker]

So, we all hear 'point the SPG away' when pressurizing in OW classes. But who has actually seen one fail?

Well, mine did today - violently. Fortunately, into my hand and not my face or any dangly bits nearby.
The behaviour was interesting enough that I'm posting here to see what discussion forms.

Scubapro compact pressure gauge (theoretically rated for 400 BAR per the website).
It's seen over 400 dives, roughly 60 of those on HP tanks up to a worst case of about 245 BAR.
Generally it has been treated very well. It could be mistaken for brand new based on appearance.

Connected up to HP tank for a gear check and shortly after cracking the tank the little o-ring on the back (that presumably serves as an overpressure valve) pops out.
That's odd. Push it back in, give another try - same result.
Try a third time - entire glass face pops off into my hand with quite a bit of of force.

At this point I'm worried I have a significantly overfilled tank.
Swap shops SPG on and it reads a perfectly normal 230bar, as does my transmitter.
The tank was not overfilled.

I see ScubaPro's warranty is only 1 year on gauges.
That's nice.
Why is their gear failing spectacularly under very mundane conditions...

Anything I'm missing here that would justify this failure?

 

[Bigbella]

I see ScubaPro's warranty is only 1 year on gauges.
That's nice.
Why is their gear failing spectacularly under very mundane conditions...

Anything I'm missing here that would justify this failure?

Judging from your detailed account, it just looks like you, sadly, received a punk SPG, which will have to be replaced, like that of a disposable lighter, since they're irreparable. Your recent experience is a bit different from mine, since I have experienced serial hose failures in the last few years -- particularly with the "Miflex" variety, of which I have discontinued use -- but never with the SPG cases themselves.

Most of mine are decades-old and still kicking; generally, they're quite dependable -- and why they have been around for so long.

As an aside, there are actually very few manufacturers of SPGs themselves -- primarily Italian, like TermoIndustria Milano, which has been around for about a century, and who have long produced gauges for many familiar brands of scuba equipment, most likely including both ScubaPro and Poseidon . . .

 

[James79]

So, we all hear 'point the SPG away' when pressurizing in OW classes. But who has actually seen one fail?

Well, mine did today - violently. Fortunately, into my hand and not my face or any dangly bits nearby.
The behaviour was interesting enough that I'm posting here to see what discussion forms.

Scubapro compact pressure gauge (theoretically rated for 400 BAR per the website).
It's seen over 400 dives, roughly 60 of those on HP tanks up to a worst case of about 245 BAR.
Generally it has been treated very well. It could be mistaken for brand new based on appearance.

Connected up to HP tank for a gear check and shortly after cracking the tank the little o-ring on the back (that presumably serves as an overpressure valve) pops out.
That's odd. Push it back in, give another try - same result.
Try a third time - entire glass face pops off into my hand with quite a bit of of force.

At this point I'm worried I have a significantly overfilled tank.
Swap shops SPG on and it reads a perfectly normal 230bar, as does my transmitter.
The tank was not overfilled.

I see ScubaPro's warranty is only 1 year on gauges.
That's nice.
Why is their gear failing spectacularly under very mundane conditions...

Anything I'm missing here that would justify this failure?

As @Bigbella said, probably just poor luck that you got a lemon that leaked internally. To add to that, though, the piece on the back that popped out is an overpressure plug... pushing it back in and trying again repeatedly is akin to replacing a fuse that keeps popping without looking for the reason it popped. I'm glad you just had the glass face pop out, rather than break (leaving sharp shards into your hand rather than a nice smooth disc).

Respectfully,

James

 

[Mike Walker]

As @Bigbella said, probably just poor luck that you got a lemon that leaked internally. To add to that, though, the piece on the back that popped out is an overpressure plug... pushing it back in and trying again repeatedly is akin to replacing a fuse that keeps popping without looking for the reason it popped. I'm glad you just had the glass face pop out, rather than break (leaving sharp shards into your hand rather than a nice smooth disc).

Respectfully,

James

That's where I think this gets the most interesting: 2 simultaneous failures in unrelated components.
The overpressure should have been the weak point and kept failing (breaker tripping in your analogy).
What caused the progression to the gauge face given the system was nowhere close to its design limits?
(The OP O-ring popped on the 3rd try as well roughly simultaneously with the face)

Since SP can't be bothered to publish a manual or assembly diagram I'm curious about the relationship.
(Though, I suppose I now have one to dissect...)

 

[James79]

That's where I think this gets the most interesting: 2 simultaneous failures in unrelated components.
The overpressure should have been the weak point and kept failing (breaker tripping in your analogy).
What caused the progression to the gauge face given the system was nowhere close to its design limits?
(The OP O-ring popped on the 3rd try as well roughly simultaneously with the face)

Since SP can't be bothered to publish a manual or assembly diagram I'm curious about the relationship.
(Though, I suppose I now have one to dissect...)

Inside the guage is a simple bourdon tube, and it is all inside the same outer housing. A leak in the bourdon tube itself allows tank pressure into the housing (that was never meant to hold it).... my guess with yours is that the pressure relief plug popped as designed, but not before the guage face was stressed. Repeat that a few times and the face popped the last time before the plug. The lack of a diagram from SP is really just a case of them designed to be a sealed unit, never expected to be opened or repaired.

Respectfully,

James

 

[Mike Walker]

Inside the guage is a simple bourdon tube, and it is all inside the same outer housing. A leak in the bourdon tube itself allows tank pressure into the housing (that was never meant to hold it).... my guess with yours is that the pressure relief plug popped as designed, but not before the guage face was stressed. Repeat that a few times and the face popped the last time before the plug. The lack of a diagram from SP is really just a case of them designed to be a sealed unit, never expected to be opened or repaired.

Respectfully,

James

View attachment 756670

Thanks, that makes sense. So the OP actually relies on a sequential failure in an OP scenario: first the tube fails and then the subsequently the OP blows before the face/housing does. Unlike a burst disc the OP is a one-time use situation since it is downstream and indicates the internal tube has already permanently failed.

Interesting.

 

[James79]

Thanks, that makes sense. So the OP actually relies on a sequential failure in an OP scenario: first the tube fails and then the subsequently the OP blows before the face/housing does. Unlike a burst disc the OP is a one-time use situation since it is downstream and indicates the internal tube has already permanently failed.

Interesting.

Yep, but within reason "over pressurizing" the gauge (Like putting a guage that tops at 3500 on a 4000 psi tank) typically will just ruin the calibration on it. The over pressurization that the blowout plug is for is an over pressure of the housing, which can only happen from an internal failure of the bourdon tube.

 

[L13]

Yep, but within reason "over pressurizing" the gauge (Like putting a guage that tops at 3500 on a 4000 psi tank) typically will just ruin the calibration on it. The over pressurization that the blowout plug is for is an over pressure of the housing, which can only happen from an internal failure of the bourdon tube.

The second failure was not the blowout plug coming out. It should ALWAYS come out if there is a leak in the bourdon tube. The actual second failure was when it didn't blow out, allowing the housing to overpressurized and blow out the glass.

 

[BoltSnap]

The safety feature of the gauge did it's job properly but your trying to "fix it" wasn't proper. You can't blame SP for that.

 

[James79]

The actual second failure was when it didn't blow out, allowing the housing to overpressurized and blow out the glass.

The safety feature of the gauge did it's job properly but your trying to "fix it" wasn't proper. You can't blame SP for that.

Agreed, the blow out plug popping was it working as designed, and repeat attempts to overcome that safety feature (reinserting the plug) resulted in the faceplate failure.