O-ring and SPGs

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icechip

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While in the pool the other day, my o-ring on my SPG went. Lots of bubbles as I lost tank air until I shut off the valve and ended my time in the pool. Got me thinking that if it had been an actual dive, this would have been an OOA. My question is, other than investing in an AI hose-less computer and transmitter and not have any SPG hose, is there (or could there be) some way for an old style SPG on a hose to be disengaged or shut down during a dive if the o-ring were to go? Just wondering.
 
Which o-ring was affected? If it was the o-ring between the hose and the SPG, then the reality is that you were probably not in jeopardy of an OOA situation. In fact if your high pressure hose bursts, blows an o-ring, etc...you have plenty of time to make a safe and slow ascent with a safety stop, presuming you were properly managing your air in the first place.

The orifice at the end of a high pressure hose where it attaches to the 1st stage is quite small...this is to restrict air flow in case of such casualty.

The opposite is true of a low pressure hose rupture.....you will lose a lot of air very very fast as the orifice at the hose/1st stage junction is relatively much larger to increase the flow of air to the diver while breathing.

Adding an AI transmitter and removing the SPG would not eliminate the potential for o-ring failure. There will still be an o-ring on the threads of the transmitter that screw into the 1st stage.

Some divers who use an AI transmitter will use a short hose to attach the transmitter to the 1st stage...this reduces the chance of transmitter damage due to someone grabbing/lifting the tank/regulator assembly by the transmitter mistaking it for the tank valve. This will add an o-ring to the hose - 1st stage interface and often will add 2 tiny o-rings on a high pressure spool at the hose - transmitter interface....this makes things on par with the number of o-rings in an SPG setup (not including the o-ring to seal the case of the AI transmitter itself).


Here is a good video by Scuba Toys that better shows how long you have when suffering a high pressure hose failure.


-Z
 
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Which oring? The hp hose-to-1st stage? Or one of the tiny spool o-rings?

going AI will only eliminate the tiny spool o-ring connection. And honestly, most issue I have seem from there are just tiny "champaign" bubbles, where gas loss will be minimal. These are often a neglected maintenance point. My bet is a total spool oring failure is from a pretty old o-ring or hasn't been cleaned and serviced in a while.
 
There are in-line shutoff valves for 2nd stage hoses....these are sometimes used on stage bottles that have only one 2nd stage....with this setup it is heavily suggested that an over-pressure fitting be added to the 1st stage.

-Z
 
My first question was when was it last serviced? I've seen lots of people dive with champagne bubbles on gear obviously not getting around to changing the O ring before it gets too late (not suggesting you have done so)

In my experience 90% of gear failures is from lack of preventative maintenance and as mentioned above spools are often ignored. I ghave all my O rings changed on an annual basis
 
The key to the long video is this picture:
upload_2018-4-1_7-43-14.png


The picture of the hose fitting on the left is a High Pressure hose inlet fitting (fitting to the tank). As you can see there is a restrictor, pin hole sized orifice, on the inlet fitting. This orifice allows pressure to flow thru to the other end of the line (to a SPG or pressure sensor) but limits the volume thru it. In the event that the hose leaks or is completely severed it would take about a half hour to deplete a standard tank. This should reduce the risk of an OOA situation and allow the diver to exit the dive in a controlled manner. As a double safety most 1st stage regulators also have a similar orifice incorporated in the internal gas path to the HP ports so if a hose or plug came loose you should still have plenty of time to do a controlled exit.
A low pressure hose on the other hand has no restrictor and is designed to deliver large volumes of IP (LP) air to the user. When it goes the bottle will empty very rapidly.
 
Having an SPG spool O-ring start leaking on a dive, isn't even a reason to scrub the dive unless it is a particularly critical one. As indicated, the loss is likely fairly trivial, especially when the leak is small which it generally is. I wouoldn't start a dive with a full HP hose failure or suspected one, but I've done a number of dives with a leak.

Shutting down the hose also stops you from having any info about tank pressure remaining, which I consider a very valid reason to scrub the dive. I'd rather have a leak and know what tank pressure is.

Leaks from the LP side are a completely different matter, emergency scale!

For reference: Life Ending Seconds • ADVANCED DIVER MAGAZINE • By Curt Bowen
 
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To me the in-line shutoff valves just mean two more hose connections, plus the valve mechanism and another o-ring to leak. O-rings do need to be pre-emptively changed from time to time.(G)
 
I would not add anything to be able to shut it down either. I have had a dive buddy develop a leak by the crimp on a HP SPG hose. We finished the dive without issues.

We always have a spare, lubed and ready to go SPG spool in our kit. Cheap, small, easy to change.
 
Which o-ring was affected?

Yes, it was the o-ring between the hose and SPG. Thank you for the video.
 
https://www.shearwater.com/products/teric/

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