Reserve Valves - How Do You Use Them?

[SurfLung]

- Without a pressure gauge, I used to dive until I was empty and just come up when I got that first difficult breath. There are usually 2-3 difficult breaths left in a DH when you go empty... I haven't done it for awhile but that's the way I remember it. Anyway, from then on, I knew about how much time I had with a tank and would use my watch to time my air consumption. But these were lake dives of usually the same 15-25 ft depths.
- In recent years, I've dived at Fortune pond down in the 80-127 ft depths and using a pressure gauge, I was shocked at how much quicker the air gets used up at deeper depths.
- Watching my computer for no decompression bottom time while keeping an eye on the pressure gauge so I've got enough left for proper assent... Well, it doesn't seem possible to do it right without actually KNOWING the remaining air pressure.
- My Dad used to say you can't get into trouble with a single 72 cf tank. Dive until you run out of air at any depth and it won't be longer than no decompression time. So in that case, I can see the reserve just letting you have the air to breath as you ascend rather than a free ascent (IF the single 72 story is true... Is it?).
- But what about diving doubles or triples. How do you know how much air you're using when diving different depths. Run out of air with some decompression stops and the reserve isn't going to give you enough time... Right? So how do you estimate or know your air consumption at changing depths without a pressure gauge?

[luis]

-

- My Dad used to say you can't get into trouble with a single 72 cf tank. Dive until you run out of air at any depth and it won't be longer than no decompression time. So in that case, I can see the reserve just letting you have the air to breath as you ascend rather than a free ascent (IF the single 72 story is true... Is it?).

That concept can be easily proven to only apply in relatively shallow water and if you are not a very light breather. All you have to do is some basic air consumption calculations and compare it to the NDL (no decompression limits) from any dive table.

I remember doing those calculations for class in the early 70’s.

The calculations are obviously going to change a lot depending on what you assume for your SAC (surface air consumption), but with a reasonable SAC you can start exceeding your NDL (from a single dive) at around 80 ft (or 90ft).

You do need very good SAC to get into trouble much shallower than that, but it is very possible. And of course, if you do any repetitive diving you could easily exceed your NDL with your second steel 72, at much shallower depth.

A simple air consumption calculations as a function of depth will show you what I am talking about.

The calculations are easy, we did them without a calculator back in 71 (I would have a real hard time doing it without a calculator now-a days). But now I can do it using Excel and even plot some graphs for different SAC as a function of depth and superimpose the some NDL numbers from a dive table. I will do that later and post the graph.

[Herman]

Bet I can can get into trouble on a 72.....I went into 5 minutes of deco on a AL-80 on Bonaire ....and still had 1500 psi in the tank. Guess that is what you get for diving with Barlowe.

[Ron]

Back when I was still diving on the regular with a buddy, I did some math and laminated a predive reserve card for j valves. It looked like this:

Emergency gas plan, which covered a loss of gas emergency at depth for a diver, where two divers would ascend on a single SCUBA:

130 feet = 20.5 cubic feet
120 = 17.6
110= 16.1
100 = 14.6
90 = 12.1
80 = 10.9
70 = 9.74
60 = 7.5
50 = 6.6
40 = 5.7
30 = 1.9

Calculations assume 1 minute at depth on reserve solving issue, and a buddy breathing ascent on a single SCUBA with 1.0 CFM for ascents.

I then compared this to my other table on the back of the card, which is the mathematical amount of gas held in reserve by my various tanks. For argument's sake, most singles have a 300 psi j valve spring, and most doubles have a 500 psi spring. If you multiply that by the tank factor of that tank, then you have a good guess as to the reserve, like this:

Single 70 reserve = 8.5 cubic foot reserve
Single 72 = 8.6
Single 80 = 7.75
Double 70s = 14.25
Double 72s = 14.4


Then, I pick the tanks dependent on the target depth. Also, if I'm in the springs, I just dive until I get bored, then swim up lol. I have summed all of this dumb math in a simple mantra for gas planning without a SPG:

Single tanks for 60 feet or less if you want gas reserves
Double tanks for 60 feet or more if you want gas reserves

Most of this was when we were doing short decos on back gas. I inspect my j valves at every fill. FWIW. This same table could be used for solo, as since it is written off of buddy breathing it would still use the same gas for a single diver on the ascent. This is only assuming that you want a gas reserve for your ascent, and that you are not going to CESA. I knew I could CESA, but my buddy at the time was much older than me, and I wasn't sure if he wanted to do a 60 foot CESA, so I carried reserve gas because I figured it was easier than towing a diver with an embolism back to the boat. It really all depends on your risk tolerance. This table is, in my opinion, a very safe way to vintage dive with a responsible amount of extra gas.

[Ron]

Also, never compare SACs with Greg, he is a fish.

[luis]

The charts below shows times versus depth.

It assumes a constant depth with a constant air consumption.

The No Decompression Limits were taken from the Navy and the NAUI tables.

You will notice that with reasonably low air consumption a diver could exceed the NDL even at 60 ft.

The first is using only about 63 cu ft (which is approximately what you get without the reserve). The second graph is using all 72 cu ft.






I just added another chart. This one is for double 72s. Again, this are simple calculations that assume that everything stays constant. It will give a general idea of how much time you have at depth (for different air consumption).

Anything to the right of the NDL means you have a deco stop obligation.





I hope this helps.

[Bryan]

Also, never compare SACs with Greg, he is a fish.

Greg (the lung) Barlow

[SurfLung]

- Thank you all for the information, and personal tricks, techniques. I think I am lacking in some knowledge on calculating air consumption. The only "How To Dive" book I can find at home is my Dad's old "DIVE" by Dick and Barbara Carrier. Whatever books I got when I took the NAUI course back in '69 I can't even remember much less find.

[1969ivan1]

I simply subscribe to the Allan K school of diving with a j valve .

[SurfLung]

- I emailed Allan K and got some humorous as well as valuable advice. He is at least as pure vintage in skills and practice as you are... Sent me some inspiring photos of you two diving full out vintage with triples and twin 38s... Nice!

[Herman]

Here is the way I do it..
Push rod up.
Go diving
When breathing gets hard,pull rod down
Go up.
If breathing gets really hard, go up faster.

[21]

Herman,
You were apparently the only one to answer the OPs question..

I will ad a few tid-bits from SoCal diving of years gone by..

We always reversed the valve "Cam" (for lack of the proper name)
So to active the J valve the diver had to push it up, rather than down.
The reason was Kelp..always an entanglement and the Jvalve was generally accidently forced down some time during the dive.

We also seldon used the pull rod, electing to reach over the shoulder to activate the valve to the up position. Easy to perform with the ealy equipment, however there were ocasions when you would like to see the ole arm grow an inch or two, maybe as much as six inches to reach the valve.

On those rare occasions when it was impossible to sctivate the J valve...
it was:
Blow and go
Flare and you are there!

SDM

[luis]

Here is the way I do it..
Push rod up.
Go diving
When breathing gets hard,pull rod down
Go up.
If breathing gets really hard, go up faster.

Yeah, I did that a several times back in the early 70’s. But, it gets old real quick when you get to the surface and realize that you have a long swim back to shore using your snorkel.

It is even more annoying when you reach the surface and you can’t see the small island we started the dive from. We could see the mountains of Puerto Rico, but that was not the direction we needed, to get back to shore. That is when you really trust your compass.

I remember in one occasion, a couple of my friends dropping their weight belts. We had a long swim with our snorkels and they didn’t have any flotation device. If I recall correctly, my buddy and I both had Fenzy so we could have carried their belt, but they were too quick to drop it. I thought about retrieving it, but it was fairly deep, and I don’t know if I had enough air.

Their weight belts probably had only 2 to 4 pounds, but the cost of a new belt was an issue for a high school student.


It wasn’t long before I got myself an SPG and started planning my dives a bit so that I could return underwater… not on the surface.

From the time and depth information, I have a fairly good idea of what my SPG is going to read, but I guess as an engineer, I like to see actual data… that is just me.


I did like J valves and had them on all my tanks even when I used an SPG.
I used to trick the reserve so that we could leave 50 to 100 psi inside the tanks when we flew from PR to St Thomas. The airline attendant would open the valve, but no air would come out.

When we arrive in St Thomas I would close the valve, disassemble the reserve, and replace the actual working lever shaft. Then we could go to the local dive shop to get an air fill without any questions of bringing in an empty tank.

[21]

Luis
Re: St Tomas
Did you frequent VDS Virgin Island Diving Schools on the peir owned by Marv Ellis?
Marv was a Texan but lived in OC and was certififed as an LA Co UW instructor.

He moved to the VI when it was unknown and open VDI.

During the time you were visiting VI I was teaching part time a local Community College and sent a number of ex-students to him for their first employment in the dive industry..Most returned back to So Cal after a year or so..
SDM

[ebj]

Can someone tell me what CESA stands for. I can still remember my instructor teaching us how to "blow and go" after running out of air. It was really special to get a tank with a J-valve, because with no pressure gauges you knew running out of air was a sure thing. Thanks Sam for the memories! None of the guys I dive with ever heard the term "blow and go".