Why would a reg become difficult to breathe from?

[MrChen]

And here's another thought, should you find yourself in the situation that began the experience. If you have a good working regular set with a blown high pressure hose, take the high pressure hose from the rental set and put it on your set.

I suggested it and they said they aren't allowed to.

 

[MrChen]

Another possibility, which I have seen in the past. It has nothing to to with the the regulator itself:

Debris from the cylinder can partially block the dip tube of the valve. On aluminium cylinders a big ball of aluminium-oxide greater than 3cm in diameter can easily develop. On steel cylinders like ECS, the base metal does not form a powder, but big flakes of rust, very thin and a good 3cm long.

If a diver goes down head first or does a overambitious back roll, this debris can fall on to the dip tube, partially blocking it. As there is no imbalance between the cylinder and the inside of the valve until a diver inhales, the debris can just sit loosely lodged in the tube. Breathing becomes harder as the diver empties the air from inside the regulator and hoses, while some air may bleed past the partially blocked tube. If the pressure imbalance gets high enough, the debris may get dislodged and usually broken up into smaller pieces, allowing more or less normal breathing.

Chances of this are very low. I thought the first time I have seen it happen it's a one in a billion chance, but it did happen again at a later stage. It of course has nothing to do with you using the pre-dive switch. In a situation like this, the person usually abruptly moves his body, which may also help to dislodge whatever is in there.

As I could not believe it after I have seen it for the first time, I experimented with an old ECS cylinder in the workshop and sure enough, if the bottle is flipped as in a fast back-roll, this can happen.

Without the cylinder turning upside down at some stage, this is impossible to happen, as the air would not suck the debris up the cylinder.

Here's some more details: I had the hydro done on my tanks within the last 3-4 months. One tank did get tumbled, but it wasn't the one I was using. My tanks are steel Worthington 120s.

Could it have been debris in the first stage went through the hose to the 2nd stage or just debris in the first stage and I was lucky that no incident occurred on the first dive?

The first stage "knob" is just a pre-dive/dive adjustment. It not an actual knob, more like a lever shaped like a knob.

Was this your own cylinder or the dive operators? If yours, I'd get it VIP'ed right away if so. If there is any corrosion that may be your issue. Get the valve serviced at the same time as well and pay close attention to the dip tube.

Yes, my tanks, and recently serviced with a hydro.

 

[ChrisMBC]

Here’s a diagnostic question: was it a lot of effort to get any gas to come out? Or was it easy to start the flow of gas, but the volume was not sufficient?

 

[Zef]

Did the reg set they gave you have rubber hoses or braided flex hoses?

The only thing I can think of that would cause a 2nd stage to go from breathing easy to breathing difficult and then back to easy with a turn of the dive/predive lever is if the inner hose of a braided flex hoses deteriorated and a piece blocked up the 2nd stage but was then dislodged by movement of the venturi lever.

Knowing what kind of hose connected the 2nd stage to the 1st stage would help.

-Z

 

[MrChen]

Here’s a diagnostic question: was it a lot of effort to get any gas to come out? Or was it easy to start the flow of gas, but the volume was not sufficient?

I had to suck pretty hard, but I did get air.

 

[MrChen]

Did the reg set they gave you have rubber hoses or braided flex hoses?

The only thing I can think of that would cause a 2nd stage to go from breathing easy to breathing difficult and then back to easy with a turn of the dive/predive lever is if the inner hose of a braided flex hoses deteriorated and a piece blocked up the 2nd stage but was then dislodged by movement of the venturi lever.

Knowing what kind of hose connected the 2nd stage to the 1st stage would help.

-Z

They were rubber hoses.

 

[Zef]

The first stage "knob" is just a pre-dive/dive adjustment.

Did you mean to type 2nd stage?

-Z

 

[ChrisMBC]

I had to suck pretty hard, but I did get air.

I’d be interested in other people’s opinion, but I wonder if it could have been something obstructing the lever, which was knocked loose by turning the Venturi knob. Even a piece of debris in the housing?

In theory, high cracking pressure + low gas flow would point towards a problem with the lever (I’d think) rather than something obstructing the flow of gas out (which wouldn’t effect cracking pressure as much).

I have no actual experience in this though, just the experience of a lot of ‘challenging’ regulator assemblies after Mr Singler’s regulator course…

 

[Tanks A Lot]

Could it have been debris in the first stage went through the hose to the 2nd stage or just debris in the first stage and I was lucky that no incident occurred on the first dive?

Debris going from the cylinder, through the first stage, into the second stage is very likely indeed. Debris from the cylinder that makes it to the first stage would start to clog up the sintered filter. All sintered filters that I have seen from the big manufacturers will not break into pieces, but rather clog up and stay that way. They will grow progressively harder to breath the more debris they catch, until at some point they do not let air through at all. They do not break though.
Some off-brand filters do buckle when clogged up completely and pressurized. This is easy to see if you just look into your first stage inlet. They usually do not break into pieces, but rather split.

Different steel cylinders rust very differently. A Faber cylinder would develop a fine powder, which can't really clog up the dip tube. When still wet, this usually sticks to the walls and base. ECS cylinders, or Vitkovice do develop flakes of rust at the base, especially the ECS. I do not have experience with Worthington cylinders, so I can't speak about those.

 

[buddhasummer]

I've seen some rentals use electrical tape to cover tank inlet, I've also seen folk attach reg with said tape still in place. Tank can be fully on and can still deliver some air if tape was torn a little when reg was attached to tank. (Yoke)