Failed Regulator or Operator Error ?

[Stout]

I ran across a story a couple of days ago where a diver was complaining that a rental regulator had failed underwater and lead to an out of air situation. The ( relatively ) inexperienced diver claimed that:

The pressure gauge needle was swinging wildly at depth, no mention of what it was doing at the surface.
It was very difficult to breath through the reg at depth. no mention of breathing difficulties during the descent.
The gauge dropped from 2000 PSI to 200 PSI very quickly

The representative of the company that responded to the claims in the story responded with what I'd consider platitudes and neither confirmed no denied the possibility that the regulator might have needed maintenance or repairs so there's no admission of guilt there, so to speak.

Now I'm no gear guy BUT.....

In OW we were taught that the way regulators are designed, they fail into freeflow, not shutting themselves off and.....I've seen this before where a diver starts off breathing normally only to run out of air at depth due to not having the air turned on properly, i.e. only turned on a quarter turn.

Based on this limited amount of information I have I'm tempted to go with an operator error explanation for this incident rather than blaming the gear. I suppose it's possible that the diver had both an empty tank to start with as well as a sticky gauge

Are my suspicions correct or am I somewhere out in left field with my interpretation of just what caused this out of air emergency ?

 

[300bar]

Sounds like a valve not opened all the way.

 

[Dirty-Dog]

The fluctuating SPG is almost always going to go along with a valve that's only partially opened.

 

[TSandM]

That sounds EXACTLY like what happens when you crack the valve open -- something people do when they are taught the "open the valve all the way and then turn back a quarter turn" procedure. They get confused as to whether the valve is open or closed, and end up cracking a closed valve a quarter turn. The reg breathes fine on the surface, but down around 3 ATA or so, it no longer works.

 

[boulderjohn]

I agree that his valve was only partially opened.

If you are on the surface and breathing, the needle will swing, but you won't notice it when you breathe. Get down to a greater depth, and you will feel it while the needle swings. Get down farther and you won't get enough air and will think the tank is empty.

 

[Hawkwood]

..
The pressure gauge needle was swinging wildly at depth, no mention of what it was doing at the surface.
It was very difficult to breath through the reg at depth. no mention of breathing difficulties during the descent.
..

I showed this to a student this weekend. In about 5 feet of water I closed her valve to just a "hair" crack open. We both watched the needle bounce back and forth as she inhaled and exhaled.

As 300bar said, the valve was not open all the way. Depending on how much, the effect would not be noticed at surface, or at "shallower" depths, but would become pronounced at depth.

EDIT: Geeze, we must have all been typing at the same time!

 

[Akimbo]

I agree that a cracked valve is the likely culprit assuming the first stage filter was clean and the water was warm enough to rule out freezing. This sort of symptom can occur due to the higher gas density at depth and be OK on the surface… but rarely.

It is a good idea to take a fast deep breath while watching your SPG just before entering the water. Check the valve if the pressure drops. Abort the dive if the valve is open.

 

[boulderjohn]

EDIT: Geeze, we must have all been typing at the same time!

It's like what I hear about playing Jeopardy. The winner is not necessarily the one who knows the most answers, it's the one who is fastest to the buzzer.

 

[Stout]

Cheers and thanks for the replies

An improperly opened valve was the only way this incident made sense to me. The diver is faulting the rental outfit but, the plot thickens. The representitive from the dive op, the one who I described as spouting platitudes was not only the divemaster but the buddy as well. There would have been a buddy check, either in the water or on the surface ( I know this operator ) especially with an OW diver and I guess, technically, the buddy/DM was engaging in a little CYA after realizing that failure to/improperly check the diver's valve was the most likely cause of the incident.

The incident took place in tropical waters so freezing wasn't an issue.

I'm not looking to assign any blame to either the DM or diver here, merely determine the veracity of the divers claim that she was given improperly maintained gear to use at a shop that I'll most likely be diving with next month.

 

[underH2Oman]

It sounds like it was acting like the valve may not have been open all the way. If the gauge was a little sticky it would read inaccurate but I do not believe it would fluctuate up and down as it would still need pressure in the system to move up and lack of pressure to move down.

In OW we were taught that the way regulators are designed, they fail into freeflow, not shutting themselves off ?

This is mostly accurate but not totally. The most common regulators on the market are of a downstream design. That means that the flow of the gas is pushing against the seats that controls the open and closed phases. If a first stage problem allows the pressure in the hose (intermediate pressure) to increased the second stage would allow excess pressure to bleed out (freeflow) it usually starts as a small trickle. A blast the mask off the face thing maybe but that is more commonly a second stage issue. perhaps a freeze up in cold water causing the lever to not return the seat to a closed position.
There are some regulators that are of an upstream design. That means that it takes the air in the hose to seat the second stage. If the intermediate pressure was to increase it would cause the regulator to become slightly more difficult to breath. They are often designed to have a pressure relief mechanism built into the system. An example would be a Poseidon Jetstream where the pressure would push the second stage forward on the hose and release gas between the hose and second stage and then reset to the original position.