How much air to surface with?

[tbone1004]

yes, so there are two things to consider. You need some sort of pressure to keep the regulators happy and to keep everything from coming undone. Yoke regs at low pressure can come loose a lot easier, tank valves can start moving if a DM hauls you onto the boat, etc etc. Then you need a CF requirement that is what you need to surface with safely, this is your Rock Bottom calculation. Some DM's are still stuck in the stone age and if you read the backup computer thread now, there are a lot of idiots that run things and don't actually know what critical thinking is, so they go 500psi regardless of what you're diving. It sucks, but it's not worth arguing with them because logic eludes them, so accept that you have a larger tank and if you're buddies have smaller tanks and a 500psi limit, you'll be above that when you surface.

 

[Lorenzoid]

I gather that that is because of something to do with the 1st stage?

Right. It's my understanding that surface-supplied rigs use a different kind of regulator entirely.

 

[tbone1004]

Right. It's my understanding that surface-supplied rigs use a different kind of regulator entirely.

their first stages can't depth compensate due to not being at depth which is why they need special second stages, or at least specially tuned second stages. Brownies third lung is rated for 80FSW which is about 50psi of compensation from the surface. Regs have to be tuned to be able to compensate for that 50psi shift in IP.

 

[stuartv]

You're missing some things here. Ambient pressure has no bearing on a rigid tank with 50psi in it. Even on the surface, 50psi is about half a breath. What good does that do for you?

Secondly, while a surface supplied reg MIGHT function at 50' with 50psi supply gas... actually it should... you're still going to be starved for gas unless you're asleep. I exaggerate, but you get my point. The reason it won't work so great through a first stage is two fold... 1. It's still less than a solid breath. 2. 50psi doesn't really flow (and it's not being forced) through the .006 orifice size in the first stage (again, I exaggerate, but you get my point), to get to the second stage. This is the hole that reduces 3000 psi to 140psi that the second stage reg then reduces to a pressure we can breathe.

Maybe you're confusing some things? "Half a breath" is a volume (unless I'm completely misunderstanding you). 50 psi is not a volume. If you have a rigid container with an internal volume of 500 liters, 50 psi of pressure in an environment that is 30 psi ambient will carry you a long ways. OTOH, a container with an internal volume of 3 liters that has 50 psi in it certainly won't give you much to breathe.

Second, I believe the orifice itself does not regulate the pressure down. There has to be something that occludes the orifice that is involved. The spring pressure of that occlusion device is what regulates the pressure down. If part of that "spring" is actually air (because it's a balanced reg), then that spring will get weaker as the tank pressure drops, which means air will continue to flow. If the regulator was "perfectly" balanced, then there would only be air acting as the spring and the air would continue to flow from the tank until the tank pressure was exactly equal to ambient pressure. If there's a mechanical spring, then the air would stop flowing when the tank pressure was higher than ambient by the pressure of the mechanical spring (putting it in somewhat simplistic terms).

One of the previous posters already stated that when the tank pressure drops below the IP, a balanced 1st stage will stop restricting the flow at all and becomes no longer part of the equation. What you are saying implies that that was incorrect. But, it sounds (very nearly) correct to me (only allowing for the presence of a mechanical spring still having some effect).

 

[Superlyte27]

The frightening part that Tbone alludes to, that most people in the recreational industry DO NOT get is that Dive Masters by and large are not much more than OW divers who were able to buy a certification.

Look at the requirements to become a "Dive Master". PADI says just 40 dives to start the course, 60 to finish it. Guys, I was a guppy at 60 dives. And most of those 60 dives were caves or wreck dives before I was certed. LOL (Don't do that. I'm lucky to have lived)

But 60 dives and you can be a person who has MASTERED diving? Show me that person. He doesn't exist. Most can't even master buoyancy and trim in that amount of time, let alone 5 different methods of propulsion, 6 different ways to clear your mask, an ability to lead and possibly save multiple divers in the ocean? YIKES!!! The thought of it makes my heart race.

So, this guy who could have done 30 dives in a quarry, then paid someone instructor who's running short on money a thousand bucks, gets a card that anyone can get that dictates they advise you on gas management? Most of them can't run a multi-level dive on tables. And you're trusting their advice on when to surface? No thank you.

Honestly, the instruction you've received so far is probably average. sadly.
My advice to everyone out there looking for instruction... Find an instructor who is diving a level higher the types of dives you ONE DAY wish to do. Find one that makes dives for fun that have nothing to do with teaching a class. Because this is one of the only ways you're going to know if that instructor is still passionate about scuba, or just does it because he needs a paycheck. There's nothing worse for the dive industry than the guy who teaches because he has to in order to eat. I want to earn a certification, not buy a certification.

 

[stuartv]

Come to Florida. I'll give you a cavern class. You'll learn what real gas planning is. And your life will be changed forever. And, you'll be a safer diver.

LOL I think I had a real gas planning class, recently, as part of Intro to Tech, AN, and DP. That is not the issue here. I am asking about guidelines for recreational dives where people generally don't do real gas planning.

Also, I am originally from Tallahassee and have already talked to Edd Sorenson about wanting to take his Cavern Class. I'm hoping to do that around the end of Nov or early Dec when I go home for a visit. After hearing so many times how crap all the instructors I've had are, I'd like to take Edd's class and see for myself how crap all my previous instructors were.

 

[Superlyte27]

Maybe you're confusing some things? "Half a breath" is a volume (unless I'm completely misunderstanding you). 50 psi is not a volume. If you have a rigid container with an internal volume of 500 liters, 50 psi of pressure in an environment that is 30 psi ambient will carry you a long ways. OTOH, a container with an internal volume of 3 liters that has 50 psi in it certainly won't give you much to breathe.



Second, I believe the orifice itself does not regulate the pressure down. There has to be something that occludes the orifice that is involved. The spring pressure of that occlusion device is what regulates the pressure down. If part of that "spring" is actually air (because it's a balanced reg), then that spring will get weaker as the tank pressure drops, which means air will continue to flow. If the regulator was "perfectly" balanced, then there would only be air acting as the spring and the air would continue to flow from the tank until the tank pressure was exactly equal to ambient pressure. If there's a mechanical spring, then the air would stop flowing when the tank pressure was higher than ambient by the pressure of the mechanical spring (putting it in somewhat simplistic terms).

One of the previous posters already stated that when the tank pressure drops below the IP, a balanced 1st stage will stop restricting the flow at all and becomes no longer part of the equation. What you are saying implies that that was incorrect. But, it sounds (very nearly) correct to me (only allowing for the presence of a mechanical spring still having some effect).

I was speaking in terms of scuba. Since I've yet to see a 500 liter scuba tank, let's just assume that any single tank you purchase, 50psi is not a full breath.

-edit-
upon further contemplation... My lungs are 6 liters. So half a breath would be 3 liters. That my friend is volume.

I'm a technician for almost a dozen different regulators. On every single one of them, there is a seat and a cone. That seat is held down against the cone by a very thick spring. The only thing that can move that seat away from that cone is 140psi or more. So, no tank pressure or low tank pressure, seat is fast against teflon seat, no gas can go in or out.

 

[stuartv]

Honestly, the instruction you've received so far is probably average. sadly.
My advice to everyone out there looking for instruction... Find an instructor who is diving a level higher the types of dives you ONE DAY wish to do. Find one that makes dives for fun that have nothing to do with teaching a class. Because this is one of the only ways you're going to know if that instructor is still passionate about scuba, or just does it because he needs a paycheck. There's nothing worse for the dive industry than the guy who teaches because he has to in order to eat. I want to earn a certification, not buy a certification.

My OW and Tech instructors have all been Trimix and Adv Trimix divers, several who also do CCR a lot. At least a couple of them are instructor trainers, also. And none of them teach because they need the money. Nor do they charge much. *I* didn't say they were crap. I just said that lots of people on SB have told me my instructors were crap.

 

[Superlyte27]

LOL I think I had a real gas planning class, recently, as part of Intro to Tech, AN, and DP. That is not the issue here. I am asking about guidelines for recreational dives where people generally don't do real gas planning.

Maybe, depends on agency and instructor. If you think surfacing with 500 psi is enough for an Ocean dive, I'd contend that you either had bad instruction or didn't listen.

I beg of you, please report back how class goes with Ed.

---------- Post added September 9th, 2015 at 05:07 PM ----------

You're not the only one who reads this page. Sometimes, it's not about you.

 

[redacted]

You're missing some things here. Ambient pressure has no bearing on a rigid tank with 50psi in it. Even on the surface, 50psi is about half a breath. What good does that do for you?

Secondly, while a surface supplied reg MIGHT function at 50' with 50psi supply gas... actually it should... you're still going to be starved for gas unless you're asleep. I exaggerate, but you get my point. The reason it won't work so great through a first stage is two fold... 1. It's still less than a solid breath. 2. 50psi doesn't really flow (and it's not being forced) through the .006 orifice size in the first stage (again, I exaggerate, but you get my point), to get to the second stage. This is the hole that reduces 3000 psi to 140psi that the second stage reg then reduces to a pressure we can breathe.

In an Al80, 50 psi is more than 1 cu ft. The typical volume of a resting breath is about .5 liters. For scuba and breathing deeply as we are taught, lets call it 1 liter. 1 cu ft is 28 liters. WOB will be quite a bit higher if that is the last 50 psi in the tank, but it is there for the taking unless the restricted breathing leads to panic. 50 psi is about 30 breaths.

The pressure in a balloon is only slightly over ambient, like maybe 1 psi over ambient. Scuba regulator opening is a bit smaller but less than an order of magnitude. Scuba is using a longer straw but you could always go to your alt to shorten that - I doubt if it will make any noticeable difference.

The problem is the gas is there but it will be more work to get it. And working harder when you feel you are not getting enough will not help.