miketsp
Contributor
..snip..
Has anybody even heard of a gauge sending "shrapnel" in the last 20 years? 30 years?
..snip..
..snip..
"Explode" and "shrapnel" are overstatements. The worst case scenario would really involve the face plate popping off, something that is really a relic of a bygone era of instrument design.
..snip..
..snip..
First off, the whole "exploding SPG" notion is a relic of a bygone era, and a false argument. Has anyone reading this ever ... in, say, the past 20 years ... seen an SPG explode? I know I haven't.
..snip..
As far as the SPG example goes, all of my SPGs have a built in failure point in the case should the bourdon (sp?) tube fail to contain the HP. On most of them, it is a small rubber plug in the back of the SPG but on one, the plug is on the top. I have never seen or heard of one failing in that mode. I watch the SPG as I turn on the gas.
..snip..
If the comments above are to be believed then I come from a bygone era.:depressed:
I was on a boat a couple of years back when one blew and although it certainly couldn't be described as an explosion it was a good "pop" and the pieces of the plastic (not glass) faceplate came out at enough speed to leave marks in the woodwork. They certainly would have made a mess of someone's face or eye.
After the initial pop the ensuing leak was of course very minor due to the pin-hole limiter in the hose.
As for the safety plug, until recently I had 2 Italian SPGs purchased in 2002, each with over 300 dives and they started giving problems (sticking) within a couple of months of each other. Since I like to know how things work I dismantled both. One did in fact have a corrosion point on the Bourden tube and the other was still pristine inside. However, the point is that neither had any sort of pressure relief plug. Both were solidly constructed, hermetic brass housings and the only place for any Bourden tube leak would be out through a shattered face-plate. And there was no way that the face-plates would just "pop" out. They were held in place by a screw down metal rim overlapping the face-plate by some 4 - 5 mm.
Edit added after discussing pressure relief of Bourden gauges with a maintenance mechanic at the company I work for. Although he wasn't familiar with diving SPGs he does work a lot with industrial gauges.
He told me there is no standard practice. Some manufacturers have no relief mechanism but these generally use safety glass that is supposed to granulate when sujected to an explosive internal pressure. Others have a plug that in fact serves a dual role allowing the gauge to be glycerine filled for use in situations where there is vibration. Others have a "disc" - a stamped weakened area in the metal housing that is supposed to give way when sujected to an explosive internal pressure. And some even have a fancy pressure release valve with a spring loaded mechanism.
Last edited: