Failed Regulator or Operator Error ?

[mala]

I have witnessed an spg needle reading low during inhale on a 30m dive.
All pre-dive checks were fine including the cylinder valve open correctly and regs breathing fine.

The dive was aborted early and on further investigation later it was found that the tank valve was faulty in such a way that even when the knob was turned fully open the valve was only slightly open.

just saying .

 

[Stout]

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.

Thanks for the info. I'd never heard of an upstream design before. In this incident there was no mention of the diver using an octopus, nor any mention of air leaking from anywhere so I was *assuming* some sort of first stage failure if it turned out that there was a possibility that the reg might have been faulty.

---------- Post added December 17th, 2013 at 10:54 AM ----------

I have witnessed an spg needle reading low during inhale on a 30m dive.
All pre-dive checks were fine including the cylinder valve open correctly and regs breathing fine.

The dive was aborted early and on further investigation later it was found that the tank valve was faulty in such a way that even when the knob was turned fully open the valve was only slightly open.

just saying .

Interesting....

Is that something that happens with any sort of frequency ? Is it something that someone could fault a rental outfit for not discovering ? There's no mention of any sort of investigation WRT the reg or tank valve from the operator and it's kind of alarming to think that, were a faulty tank valve the cause of this incident, that I may be soon using that very same tank or valve.

 

[John C. Ratliff]

I would like to add a couple of points here. First, about the fail-safe free flow; that happens like has been discussed above for a first stage overpressure (high pressure air bypasses the first stage valve). But this is not the only type of first stage malfunction that can occur. Years ago I witnessed a diver allow sea water to get into the first stage of his regulator without the "dust cap" (which is actually a waterproof seal) on the regulator. This allows corrosion to form on the first stage, and the "sintered filter" which would restrict air flow at high demand and/or depth. In the tropics this can happen very quickly too, due to the heat and humidity.

Second, I investigated a fatal accident in 1987. I was asked my the coroner's office to produce a report on his death. I won't bore you with the four-page single-spaced report, but one detail has bearing here:

...The regulator was made by SCUBAPRO, and consisted of a Mk V first stage updated to include a Mk 10 cap, and an adjustable second stage of the same manufacturer. The second stage was without its exhaust tee; the 1st stage yolk retainer was loose. The second stage adjustment was tightened all the way down. Interstage pressure (tested after removing the low pressure inflator hose) was approximately 135 psi, which is at company specifications. Upon initial placement of the regulator on the test tank, there was a significant first stage air leak at the yolk retaining assembly. The "Technical Manual for Scubapro Regulators states probable cause as "a. One of the two pneumatic yolk piston O-rings is damaged. b. Damaged yoke retainer O-ring." and goes on to say that the suggested remedy is to "Return regulator to dealer for repair." I inspected this O-ring, and it was dry (unlubricated)...

3. Possible regulator malfunction--Second Stage: The regulator was missing the exhaust tee, which could have allowed water seepage into the second stage housing. THis is especially possible due to the high suction pressure needed to open the demand valve (see below). This would have made it a "wet" breathig regulator, and if it occurred over the whole dive, could have allowed enough sea water to enter the lungs in the form of a fine mist to impede oxygen transport from the lungs to the bloodstream. (See Skin Diver Mapazine, May 1987, "I learned about diving from this" for an account of this type of an accident).

4. Regulator malfunction--Second Stage: Breathing resistance was very high. The regulator was leaking air prior to the dive, and then the adjusting nut was screwed down by Mr. XXXXX to stop the leak. It was screwed all the way down. The following measurements were taken using a home-made open tube manometer:

Exhalation Resistance:
.....Cracking: 2 centimeters H2O
.....Full Exhalation (peak): 8 centimeters (3 inches) H2O

Inhalation Resistance:
.....Cracking: 10-12 centimeters (4-5 inches) H2)
.....Peak Inhalation: 26-28 centimeters (10-11 inches) H2O

This can be compared to the SCUBAPO chart for specifications on this first stage, which shows in Figure 7 a 1-4 inches of water breathing resistance for a well-tuned regulator of this brand. This would have cause quite a fatigue factor throughout the dive.

In this case, the regulator had been neglected, was being dived without an exhaust tee, and the adjustment feature abused to stop a leak when that should have led to an abort of the dive. A regulator breathing this poorly at the surface would be part of a lethal combination for this diver (there were several other factors as well).

What I am saying is that it is possible that a neglected regulator, even a very good regulator, can produce very poor breathing characteristics if abused. Rental regulators are always suspect for this kind of abuse, and so should be inspected with care prior to a dive.

SeaRat

 

[BRT]

Don't forget the possibility of debris in the tank dip tube.

 

[PsyWulf]

Meh i've had this happen due to a valve not being fully opened and getting knocked when we rolled off the boat. Worked fine on the boat,no needle movement. By the time we got down to 22m it became an issue. Kept a level head,borrowed the DM's octo while I removed my kit and sorted out the valve. I actually have this on video too accidentally since I was recording our descent when I noticed the problem :bonk:

 

[300bar]

I have witnessed an spg needle reading low during inhale on a 30m dive.
All pre-dive checks were fine including the cylinder valve open correctly and regs breathing fine.

The dive was aborted early and on further investigation later it was found that the tank valve was faulty in such a way that even when the knob was turned fully open the valve was only slightly open.

just saying .

This still comes down to a valve not fully open.
And even to operator/owner error.
The threads on the valve had been tightend way to fast for too many times.
I do have a valve like that in my workshop(marked DO NOT USE)
Treads on Part # 35069 are then damaged

 

[DivemasterDennis]

This thread is historic. When is the last time every responder agreed on the response? Including me.
DivemasterDennis

 

[Bob DBF]

J-valve in the reserve position, but I admit you don't get much of that anymore.



Bob
-----------------------------------------------
I may be old, but I’m not dead yet.

 

[beaverdivers]

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

I believe it is operator error.

We changed our training a number of years ago to the "All the Way ON or All the Way OFF" method. Perhaps it is a reoccurring problem due to a questionable training technique.

Are divers still taught the " 1/4 Turn Back " method?

 

[abnfrog]

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.

it also happens when a tank is put in backwards and the valve is closed to 1/4 turn ...breaths ok at the surface then 2ata nothing ...i think this is more likely what happened with him saying the gauge was moving up and down wildly ....