Why don't agencies teach the vacuum test? Or do they?

[johnmckenzie]

While researching for an article on ScubaGadget I noticed that of the Open Water Diver training texts and videos I reviewed, I have not found one the teaches new dive students to do a quick vacuum test on their second stages after hooking-up their regulator up to the tank; but before turning on the air (e.g. inhale on the second stages to check for leaks).

My first question: Are some certification agencies teaching this procedure in their materials? If yes, which ones?

SIDE BAR: My regulator guru explains it this way. If you have a leak anywhere in your air delivery system, from a loose yoke to an exhaust port flap folded over, a suck on the connected second stages can tell you if air is getting through somewhere. While some leaks may be found by hissing air, you cannot test for some other leaks after you turn on the air and before you enter the water (e.g. exhaust port). If you miss a leak it could mean a wet breathing regulator. The potential consequences are scary if it was a wet octo needed in an emergency.

My second questions: Is there any reason all certification agencies shouldn't add this quick vacuum test to their gear setup training in videos and manuals?

Thank you for your feedback.
John

 

[pisoiu]

I can think of few situation where this wont work
-minor leaks may be very hard to detect, you have to keep negative pressure longer than one is able to hold breath to detect a change in inspired volume
-some leaks due to tears or punctures in flexible materials (hoses) may be minimal or inexistant when the system is not pressurised and same tears or punctures may expand under pressure.

 

[johnmckenzie]

Thank you for your reply. I am not talking about a definitive test, just an extra margin of safety. For example: My exhaust port folds over occasionally if I have to use a hose for rinsing. If I do the pre-dive vacuum test it is immediately evident and I can fix the problem before a dive. If I miss the fold-over and dive with the regulator in that condition, some water is going to get into the air stream.

I can think of few situation where this wont work
-minor leaks may be very hard to detect, you have to keep negative pressure longer than one is able to hold breath to detect a change in inspired volume
-some leaks due to tears or punctures in flexible materials (hoses) may be minimal or inexistant when the system is not pressurised and same tears or punctures may expand under pressure.

 

[eponym]

My first question: Are some certification agencies teaching this procedure in their materials? If yes, which ones?
Thank you for your feedback.
John

SSI includes this step in gear assembly. It's described in a paragraph in section two of the OWD student manual, under the heading "Before you turn on the air." First step is exhaling through second stages to check for stuck valves. Second step is attempting to inhale to check system integrity. Third step is examining the mouthpieces for tears or missing bite tabs or loose (or missing) tie wraps. Fourth step is to check that the SPG reads zero when air is off, and zero out the depth gauge.

-Bryan

PS. So that's how I have them do it.

 

[tstormdiver]

SSI includes this step in gear assembly. It's described in a paragraph in section two of the OWD student manual, under the heading "Before you turn on the air." First step is exhaling through second stages to check for stuck valves. Second step is attempting to inhale to check system integrity. Third step is examining the mouthpieces for tears or missing bite tabs or loose (or missing) tie wraps. Fourth step is to check that the SPG reads zero when air is off, and zero out the depth gauge.

-Bryan

PS. So that's how I have them do it.

That is exactly how I teach it also in the equipment assembly part of the course (also SSI).

 

[chillyinCanada]

And once the air us turned on do you then have them take some quick breaths off reg whilst watching guage to see if psi measurement changes, thereby indicating air isn't turned on after all?