Exploding SPG gauge faces?

[kablooey]

I wish I'd seen this thread earlier, because I have a personal experience with a pressure gauge exploding in my face. And it was my own stupid fault.

It was one of those yoke style gauges used to test tank pressure. It was leaking air out of a plug on the back. It was some kind of over-pressure blow out plug I think. I put a small piece of masking tape over it to stop the leak, thinking it would still blow out if it had to. MISTAKE #1

I used it several times after that with no problems. So, I thought everything was fine, and I'd replace the gauge sometime soon. MISTAKE #2

One evening I was out in my garage getting my gear ready for a dive the next day. I clamped the gauge on my tank. Then leaning forward with my eyes wide open I looked directly into the gauge and turned the knob. BIG MISTAKE #3
I'd been trained not to do that. I apologize to all my instructors. You were right.

Before I knew anything was wrong I felt a not-unpleasant sensation like being punched in the face with with a big soft boxing glove. Then I heard the pop. Then I saw the blood.

The plastic gauge cover had shattered and sent dozens of plastic shards in the general direction of my face. The skin on my upper lip, chin, and both sides of my nose had been instantaneously scrapped off. They were surprisingly clean wounds, and mostly just on the surface layer of skin. I had scrapes only, no deep punctures, but the wounds bled like crazy.

You're probably wondering about my eyes?
I wear glasses.
Never felt so grateful for bad eyesight.
The lenses must have deflected the shards. My eyes were untouched.

Go ahead, I deserve whatever names you guys are going to call me. Have fun.
Just learn from my mistake. I know I have.
I don't even look directly into my wrist computer any more when I turn my air on.

K

 

[Akimbo]

How do you check for a leaking Bourdon tube?

Methods vary but most manufacturers that I have seen pressurize a bank of them (before closing the plastic or metal housing), turn the valve off, and wait for a pressure drop. Actual bourdon or helicoid failures are very rare at this stage and are more likely at the weld or solder joint between the tube and adapter block. Any mechanical pressure sensing mechanism will eventually fail from work-hardening related metal fatigue but it requires a lot of cycles.

That is one of the reasons that gauges used in high vibration industrial applications are Glycerine filled, which effectively dampens the cyclic effect on the tube and drive mechanism.

Hmmm... or did you mean to check your own gauge? I can't imagine a leak that is so slow that the housing or blow-out plug wouldn't fail before you had the chance to check.

Here is an image of an Oceanic SPG with a plastic housing and helicoid movement exposed (back cut off with a hacksaw). Note that the gauge needle is driven directly from the concentric-wound and flattened helicoid tube rather than amplified through gears like a "C" shaped Bourdon tube.

 

[divad]

I was being facetious, but sincere thanks for the elucidation. An SPG is an odd situation with internal and external pressure considerations. When the one in my (old) car breaks, it just leaks oil. The externally pressurized version is more "interesting."

 

[Bob DBF]

How do you check for a leaking Bourdon tube?

Shove it underwater and look for bubbles?


Bob

 

[MaxBottomtime]

I had the plastic cover on a small spg fire away when I opened the valve. It landed thirty feet away.

 

[Saniflush]

How do you check for a leaking Bourdon tube?

WHEW! For a moment there I thought you said bourbon tubes. For the record mine always have holes in the top of them.

 

[divad]

Have you been dwinking?

 

[Sam Miller III]

The SPG was introduced to the American diver in 1954 via a number of advertisements in Skin Diver Magazine (SDM.)

It was a new device to the American dive community, but the SPG had originally been developed, introduced and used extensively by the great French SCUBA diver, Instructor, author Yves le Prieur in 1934 (for all of your who declare they began diving before the SPG)

In 1954 the Mar Mac SPG slowly appeared on the shelves of the pioneer SoCal dive shops and a few scattered centers of diving primarily in the metropolitan areas of NY city and Chicago. It's acceptance as a diving accessory by the divers was guarded, but as all new devices of diving it was slowly accepted by a select few.

Then reports of a number of problems began surfacing...

The Mar Mac had three distinct problems

1
2
3

Yes, it was the reason divers every where are recommended (taught?) still to this day are turn the SPG face away when turning on the air supply
SDM

 

[Akimbo]

@Sam Miller III

Do you recall if the original/early HP ports had the tiny flow-restricting hole? I know it has been an industry norm for all of my life but don't know if that carried over to SPGs right away.

Also, do you recall when blow-out plugs were introduced in SPGs. Every one I have owned had one but that wasn't until the mid-1960s and certainly doesn't mean that every brand had them.

 

[EastEndDiver]

Sam Miller have you wrote a book yet about the history of diving and if no when I really like your insite and knowledge on the beginnings of diving !!