What people think of SCUBA training

[Littlerayray]

Yeah sorry, I thought you were talking about valves. Then was thinking you meant balanced first stage vs. unbalanced, the latter being something else I doubt I've ever seen.

It's all good
I'm this note does no one else feel it is important to know how the equipment you use is keeping you alive
Ie: the first stage drops the pressure from 3000 psi to 150 psi and that your 2nd stage drops it from 150 psi to ambient air pressure???

 

[TMHeimer]

It's all good
I'm this note does no one else feel it is important to know how the equipment you use is keeping you alive
Ie: the first stage drops the pressure from 3000 psi to 150 psi and that your 2nd stage drops it from 150 psi to ambient air pressure???

Yes, it's good to know those things. At least the basics. There are those who are completely familiar with every part of a regulator, which comes in handy if you work as a repairman or service your own stuff. The DM course goes into pretty detailed explanations of all the "whys" in diving--physics, physiology, equipment (ie. the dangers of painting a tank with this or that kind of paint). At least the "old" PADI course did before 2010--I don't know exactly what in those areas was trimmed down in favour of more practical knowledge, like requiring some experience in search & rescue and deep diving. I figure that other than the debate about OW not including basic rescue skills, the OW course tells you what you need to know to not kill yourself. Much more knowledge above that is very desirable, but in most cases not necessary. I have a Masters in Music totaling 178 credits, but probably used 20% of that in my teaching and playing careers.

 

[stuartv]

Yeah sorry, I thought you were talking about valves. Then was thinking you meant balanced first stage vs. unbalanced, the latter being something else I doubt I've ever seen.
I don't recall learning much detail about the 4 laws you mention back in OW course (just really basic), but that was 13 years ago, I may be wrong.

If you have ever seen a ScubaPro Mk 2, you have seen an unbalanced 1st stage.

I could be wrong, but I think any 1st stage that attaches to the tank valve on its end (versus on the side, like any higher end reg) is an unbalanced 1st stage. That design does not have anywhere for a balance chamber to live.

Besides, the Mk 2, other examples would be the Hollis HO2 O2 reg, and the various DGX and Dive Rite drysuit inflation 1st stages and O2 deco regs.

It's all good
I'm this note does no one else feel it is important to know how the equipment you use is keeping you alive
Ie: the first stage drops the pressure from 3000 psi to 150 psi and that your 2nd stage drops it from 150 psi to ambient air pressure???

I was really surprised during my IDC by one of my co-instructor candidates. He is a friend that is also a technical diver. during a classroom session during our IDC, it became clear that he didn't really understand how regs worked - e.g. 1st stage drops pressure to 140-ish, 2nd drops it to ambient. Difference between a piston and diaphragm. Difference between balanced and unbalanced. Him being a techincal diver also, I was pretty surprised at his lack of detailed knowledge in that area.

But, it begs the question, does a recreational diver really need to know those things?

A question I like to ask, to see how people respond is "if the 2nd stage is dropping a higher pressure down to ambient, why do we need the 1st stage? Why can't the 2nd stage just be the only stage, and drop the pressure from 3000 (or whatever) all the way to ambient in one stage?" So far, nobody has ever had a ready answer.

 

[Littlerayray]

If you have ever seen a ScubaPro Mk 2, you have seen an unbalanced 1st stage.

I could be wrong, but I think any 1st stage that attaches to the tank valve on its end (versus on the side, like any higher end reg) is an unbalanced 1st stage. That design does not have anywhere for a balance chamber to live.

Besides, the Mk 2, other examples would be the Hollis HO2 O2 reg, and the various DGX and Dive Rite drysuit inflation 1st stages and O2 deco regs.



I was really surprised during my IDC by one of my co-instructor candidates. He is a friend that is also a technical diver. during a classroom session during our IDC, it became clear that he didn't really understand how regs worked - e.g. 1st stage drops pressure to 140-ish, 2nd drops it to ambient. Difference between a piston and diaphragm. Difference between balanced and unbalanced. Him being a techincal diver also, I was pretty surprised at his lack of detailed knowledge in that area.

But, it begs the question, does a recreational diver really need to know those things?

A question I like to ask, to see how people respond is "if the 2nd stage is dropping a higher pressure down to ambient, why do we need the 1st stage? Why can't the 2nd stage just be the only stage, and drop the pressure from 3000 (or whatever) all the way to ambient in one stage?" So far, nobody has ever had a ready answer.

Here is your ready answer the reason for 2 steps is to help on wear and tear think of a screen door slamming that's what would happen to the reg also I believe that there was one reg that did drop from 3000 to ambient give me a second I can look it up

 

[Littlerayray]

Who knows maybe I had a great instructor maybe it's me paying attention but it could also be my wanting to know what and how things are keeping me alive

 

[stuartv]

I'm like you. I want to know. I'm just not convinced that it is a "need" to know thing for recreational divers. So, in the limited time that is available during an OW course (however much time that is, as determined by the instructor/shop), I'm not sure it's something I would go into great detail on. Actually, it is not something I go into great detail on - unless a student asks. I'll give 'em as much detail as they want.

As for the ready answer, I have my own ideas of why it is done like it is. I think there are several reasons and none of them are to do with saving wear and tear. My point was not that I am seeking an answer. My point was only that I like to ask that question to see how people who are "teaching" about regulators handle it. I think someone who really understands how regulators work should be able to come up with at least one reasonable proposition for the answer, just off the top of their head. So, my question is more of a test for the person I'm asking, regarding their poise and their real comfort with the subject, than for me to obtain a definitive answer.

 

[RyanT]

Here is your ready answer the reason for 2 steps is to help on wear and tear think of a screen door slamming that's what would happen to the reg also I believe that there was one reg that did drop from 3000 to ambient give me a second I can look it up

Years ago I had a SpareAir....bad for so many reasons. That system has an integrated 1st/2nd stage. The one I had constantly had leakage problems. I suspect as @Littlerayray suggested, it was due in part trying to bring really high pressures down to ambient, directly.

 

[tr3a]

If you have ever seen a ScubaPro Mk 2, you have seen an unbalanced 1st stage.

I could be wrong, but I think any 1st stage that attaches to the tank valve on its end (versus on the side, like any higher end reg) is an unbalanced 1st stage. That design does not have anywhere for a balance chamber to live.

Besides, the Mk 2, other examples would be the Hollis HO2 O2 reg, and the various DGX and Dive Rite drysuit inflation 1st stages and O2 deco regs.



I was really surprised during my IDC by one of my co-instructor candidates. He is a friend that is also a technical diver. during a classroom session during our IDC, it became clear that he didn't really understand how regs worked - e.g. 1st stage drops pressure to 140-ish, 2nd drops it to ambient. Difference between a piston and diaphragm. Difference between balanced and unbalanced. Him being a techincal diver also, I was pretty surprised at his lack of detailed knowledge in that area.

But, it begs the question, does a recreational diver really need to know those things?

lA question I like to ask, to see how people respond is "if the 2nd stage is dropping a higher pressure down to ambient, why do we need the 1st stage? Why can't the 2nd stage just be the only stage, and drop the pressure from 3000 (or whatever) all the way to ambient in one stage?" So far, nobody has ever had a ready answer.

US Divers "Mistral" , and others

 

[60plus]

From post #53"A question I like to ask, to see how people respond is "if the 2nd stage is dropping a higher pressure down to ambient, why do we need the 1st stage? Why can't the 2nd stage just be the only stage, and drop the pressure from 3000 (or whatever) all the way to ambient in one stage?" So far, nobody has ever had a ready answer."

Most experienced gas welders could answer that. A regulator only regulates to within a given % and has a varying high to low pressure characteristic that changes with inlet pressure. Your scuba second stage reg has to give an output that is accurate to withing a fraction of a mB. This could not conveniently be achieved in a single stage reg. If you are burning (oxy / fuel gas cutting) a single stage reg will do because the output pressures are fairly high and need not be maintained that accurately. For welding thin materials with small nozzles you need the more accurate control a 2 stage reg gives.
If you tried to use a single stage reg for scuba and it was set for comfortable breathing when the tank was at high pressure you would find it would free flow as the tank pressure dropped. MIG welding using single stage regs waste gas because of this characteristic. Single stage regs also build up more pressure when the gas is not flowing, causing a surge when flow starts.
In scuba if you had a single stage reg at your mouth, the hose between the reg and tank would have to be much more substantial than a 150 psi hose.

 

[tr3a]

From post #53"A question I like to ask, to see how people respond is "if the 2nd stage is dropping a higher pressure down to ambient, why do we need the 1st stage? Why can't the 2nd stage just be the only stage, and drop the pressure from 3000 (or whatever) all the way to ambient in one stage?" So far, nobody has ever had a ready answer."

Most experienced gas welders could answer that. A regulator only regulates to within a given % and has a varying high to low pressure characteristic that changes with inlet pressure. Your scuba second stage reg has to give an output that is accurate to withing a fraction of a mB. This could not conveniently be achieved in a single stage reg. If you are burning (oxy / fuel gas cutting) a single stage reg will do because the output pressures are fairly high and need not be maintained that accurately. For welding thin materials with small nozzles you need the more accurate control a 2 stage reg gives.
If you tried to use a single stage reg for scuba and it was set for comfortable breathing when the tank was at high pressure you would find it would free flow as the tank pressure dropped. MIG welding using single stage regs waste gas because of this characteristic. Single stage regs also build up more pressure when the gas is not flowing, causing a surge when flow starts.
In scuba if you had a single stage reg at your mouth, the hose between the reg and tank would have to be much more substantial than a 150 psi hose.

Have you ever dove a single stage regulator?