Tank Pressure

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Wetsuit
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Tank Pressure

Mon Jul 10, 2017 1:06 pm

Hello,
So I'am really new to the world of DH diving and have a question about tank pressures and there effect on DH regulator.

I'am planning on picking up a Phoenix DA Aqua Master, but want to know if my steel 120's are going to be to high a pressure for the regulator to handle. And if I should start looking for smaller tanks.

Thanks,

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Bryan
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Re: Tank Pressure

Mon Jul 10, 2017 1:22 pm

The Phoenix has a 232 bar (approx 3500psi) yoke. Unless you are doing double disc Florida cave fills you are fine. Industry recommendation is to use DIN when going higher than 3500psi.
The Phoenix first stage was designed to be compatible and used with all modern open circuit SCUBA equipment.

Some other great information can be found HERE
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

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Wetsuit
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Re: Tank Pressure

Mon Jul 10, 2017 1:53 pm

Great, Thanks so much

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2THDIVR
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Re: Tank Pressure

Mon Jul 10, 2017 7:06 pm

I use my Phoenixes (plural of Phoenix???) and Kraken on 3500 psi tanks 90% of the dives
Propably have over 100 dives on the Kraken and 300 + on the Phoenixes
never a problem, regs perform great
I have some of the early Dive Rite manifolds for the high pressure tanks that are 200 bar
broken down for singles
so I don't use Din

Scott

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Bronze06
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Re: Tank Pressure

Sun Jul 30, 2017 7:17 am

The Phoenix adapter and the Argonaut Kraken perform very well using HP tanks. Firstly, let me tell you what I've learned on this site.

Tank Pressures

Low-Pressure tanks in the present day sense, are tanks that can contain pressures between 1800psi to 3000psi using the manufacturer's description of what a low-pressure tank is. We're talking about Luxfer, Catalina, Faber and even Press Steel companies. A medium pressure tank today is considered a 3300 psi tank and a high-pressure tank is a 3442psi or even higher.
There was a time not too long ago where a low-pressure tank was considered 1800-2250 psi, with a 2475-2640psi tank being considered a medium pressure tank and a 3000psi tank was considered a high-pressure tank. This was pretty much the "standard way" of looking at tank pressures, starting from the early 1970s clear on up through the 1980's and early 1990's. As tank construction improved starting in the early 1990s with even higher tank pressures and capacities being made available, the aforementioned "Standard way" criteria changed. It should be interesting to see what happens in 20 more years.

As far as DH regulators are concerned;

A real reason a lot of folks like lower pressure tanks is the fact that they do not put as much wear on regulators. That said, Vintage regulators (from generally 1975 and before) were designed to withstand and operate under the tank pressures that were prevalent at the time of their manufacture. A vintage DH 1960 DW "Mistral" from US Divers was originally designed to operate using 1800 to 2475 psi tanks. That said, the US Navy characteristically tended to over fill their 2475 psi tanks to 2800 and even 3000psi back in the 1960s and had no ill effects. I regularly use 80cuf. 3000 psi tanks on many of my vintage regulators without having any problems. That said, it can cause more wear on attachment yokes, seats and some internals after time, but if you are maintaining your regulators with annual to semi-annual service, you should have no problems. It might be a good thing, if you are using a vintage reg a lot and using medium (3300psi) to high-pressure (3442psi) tanks, that you switch out your vintage regulator's original yoke with a modern one built to withstand those higher pressures and hang on to the original yoke for converting it back to lower-pressure operations. With the Phoenix and Kraken, you don't need to worry about this as they are built like tanks and can take super high tank pressures.

Lastly

We have to remember that when we look at an 80cuf tank that has a tank service pressure of 3300 psi, that that means that in order for you to have 80 actual cubic feet of air in the tank it must be filled to 3300psi. Generally, if you drop this down to say 3000psi, you will have approximately 90% of a full capacity fill which will equate to approximately 72 cubic feet of air. I have a 1957 Rene from US Divers that is rated for 72cuf (cubic feet) at 2250psi. It originally was what they used to call a Plus tank (+) which meant that during the first 5 years of use it could be used at 10% above the initial rated fill of 2250 psi which would be 2475psi. giving me approximately 79.2cuf of air. After 5 years it was no longer to be used at the 10% overage (they still make 10% over-fill tanks by the way "Faber" is one company that still does). It is funny to note, that it appears that people and the industry were drawn towards 80cuf and higher pressure even back then. The beauty of a low-pressure 2640psi, 95cuf tank or a 105cuf low-pressure tank is that you got ALL the cubic feet without having to jump overall pressure up. This is another reason a lot of people on this website like the higher volume of lower pressure tanks in that they get their full compliment of air with less wear and tear on their equipment, plus they don't have to compromise as with a new high-pressure tank and bleed off air to lower pressures (and lose cubic feet of air) just to be able to dive their older equipment without worry. JMO
"Where'd ya get that ol' thang, don't cha' know them thare things ill kill ya!"

Live From the Red Sea,

Russ

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luis
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Re: Tank Pressure

Sun Jul 30, 2017 12:03 pm

It is funny, the scuba industry makes up all kinds of names for many things including pressure cylinders. It is kind of convenient to call different cylinders: low pressure, medium pressure, and high pressure. But technically and legally they are all “high pressure cylinders”. The definition of high pressure cylinder comes from the CFR (Code of Federal Regulations) and CGA (Compress Gas Association). A low pressure cylinder is like a propane tank. A low pressure cylinder is up to 500 psi. Anything above that is a high pressure cylinder.

I do like some of the distinctions we make in the scuba industry, but they are more of a slang than a legal definition and that is why they are not standard and always changing.

_____________________________

The US Navy used DA Aqua Masters with 3000 psi aluminum cylinders on a regular bases back in the 60’s and 70’s. The aluminum cylinders were specifically made for the Navy under the mil-spec Mil-C-24316. The cylinders were made from 6061 aluminum alloy pipe. This cylinders were designed to be non-magnetic. The primary fabricator was PST. Bryan has a copy of the Mil-spec in the download section.

I don’t believe the Navy regularly overfilled cylinders (in the 60’s) to a pressure higher than allowed by regulations, but I do not have an easy way of confirming that. I may ask around. I do know that in today’s Navy that would not be the practice.

_____________________________

All the DOT steel cylinders built under the CFR (Code of Federal Regulations) code 3AA come plus stamped (+) from the factory and they can receive the 10% overfill when there is a plus stamp next to the most recent hydro test date. The + stamp can be renewed during any hydro test, even if it was skipped during some of the previous hydro testing.

All of my steel 72 (some dating back to the 60’s) have fresh + stamps next to their most recent hydro test. I had them all (about 18 cylinders) hydro tested in 2015 when my LDS was closing and they all have the +stamp.

A steel 72 actually holds about 71 cuft of air when it is filled to 2475 psi (that is including the 10% overfill). When they are filled to the stamped pressure of 2250 psi, they actually hold about 64 cuft.

AFAIK, manufacturers in the US have always rated their 3AA steel cylinders by giving the estimated air volume with the 10% overfill capacity.

I don’t know of any manufacturer ever offering a 79 cuft cylinder at 2475 psi (stamped 2250) , but I have no way of confirming this. I do know that the most popular cylinder offered by US Divers and others was the well known steel 72, but this actually held about 71 cuft at 2475 psi with the 10% overfill (stamped 2250).

BTW, the mil-spec for the standard steel 72 is Mil-C-24447. There should also be a copy of that spec in download section.

Here are a few paragraphs from Mil-C-24447
3.2 General. The cylinder shall be for use as the compressed air cylinder in demand type, self-contained underwater breathing apparatus. The cylinder shall conform to DOT Specification 3AA as set forth in CFR, Title 49 - Parts 1-199 and as specified herein.

3.3 Physical parameters. The cylinder shall be of open-hearth steel or equivalent, and of uniform quality, in accordance with figure 1, and have an overall length of 25 ± 3/16 inches , The cylinder 'Wall thickness shall be such as to attain the required buoyancy (see 3. 3.3) and shall have a 0.156 inch minimum thickness.

3.3.1 Service pressure and capacity. The cylinder shall be designed for 2250 pounds per square inch gage (psig) service pressure. Each cylinder shall be hydrostatically tested to withstand 3750 psig (see 4. 5.1.1). After final heat treatment, but prior to final cleaning and painting, the cylinder shall be capable of withstanding the internal hydrostatic test specified in 4.5.1.1. Capacity shall be 71 ± 1 cubic feet air supply at 2475 psig. The cylinder shall have an internal volume of 700 ± 30 cubic inches.

3.3.6 Expansion characteristics. When hydrostatically tested to 3750 psig, the cylinder shall exhibit a total volumetric expansion not exceeding 57 cubic centimeters (cc). The permanent expansion (PE) shall not exceed 5 cc, the remainder shall be elastic expansion (EE).
Luis

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luis
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Re: Tank Pressure

Sun Jul 30, 2017 12:46 pm

Bronze06 wrote:That said, it can cause more wear on attachment yokes, seats and some internals after time, but if you are maintaining your regulators with annual to semi-annual service, you should have no problems.

Hi Russ,
The higher pressures can put a bit more wear on an HP seat or some HP O-ring that does not have a back-up ring (like the one in the Royal Maste), but that is about it. An undersized yoke can in theory elastically flex a bit and that can extrude the valve O-ring (this can be bad).

But, the practice of “annual to semi-annual service” is a modern practice that goes against the basic principle of: “If it isn’t broke don’t fix it”. I do not recommend the practice of taking apart a perfectly good working regulator based on an arbitrarily short time period.

Most O-rings and other consumable parts are guaranteed for many years (most over 10 years), therefore there is no need to prematurely replace them with new unproven parts that could be out of tolerance and may need to break in to fit into the system.

The only exception to this recommendation is if you flood the regulator with salt water. Then a rebuilt is always recommended.

For a number of reasons, there are more malfunctions right after a service than in any other time in the life of a regulator.


Bronze06 wrote:As tank construction improved starting in the early 1990s with even higher tank pressures and capacities being made available, the aforementioned "Standard way" criteria changed. It should be interesting to see what happens in 20 more years.

It may seem that tank construction has changed in the 90’s, but it really has not. Some new steel cylinders are made out of higher strength alloys using special DOT permits, but the actual construction technique is actually the same.

The Europeans have been playing with much higher pressure cylinders (4500 to 5000 psi) cylinders for decades (at least since the 70’s), but they don’t seem to be getting popular anywhere.

There are a lot of reasons why the very high pressures are not very appealing. One reason is that ideal gas law doesn’t apply as the pressure gets that high. Gas compression is not linear at very high pressures. When you double the pressure from let’s say 2500 psi to 5000 psi, you don’t get twice the gas in the same volume.

Bronze06 wrote:The Phoenix adapter and the Argonaut Kraken perform very well using HP tanks.

I totally agree with that statement. :)
Luis

Buceador con escafandra autónoma clásica.

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Bryan
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Re: Tank Pressure

Sun Jul 30, 2017 2:57 pm

luis wrote:
But, the practice of “annual to semi-annual service” is a modern practice that goes against the basic principle of: “If it isn’t broke don’t fix it”. I do not recommend the practice of taking apart a perfectly good working regulator based on an arbitrarily short time period.

Most O-rings and other consumable parts are guaranteed for many years (most over 10 years), therefore there is no need to prematurely replace them with new unproven parts that could be out of tolerance and may need to break in to fit into the system.

The only exception to this recommendation is if you flood the regulator with salt water. Then a rebuilt is always recommended.

For a number of reasons, there are more malfunctions right after a service than in any other time in the life of a regulator.





Bronze06 wrote:The Phoenix adapter and the Argonaut Kraken perform very well using HP tanks.

I totally agree with that statement. :)


All of the above in spades.
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

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georgeaustin
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Re: Tank Pressure

Sun Jul 30, 2017 8:48 pm

Gas law being non linear with respect to the 4-5K working pressure tanks is something the average recreational diver has yet to come to grips with (in most cases). Those of us in industry are probably a little more familiar with what is a "phenomenon" to others.

I believe the military has uses for the DOT non approved super tanks but can't speak from personal experience. Someone else here will know more.

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Bronze06
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Re: Tank Pressure

Mon Jul 31, 2017 7:05 am

Luis, you are fricken amazing! Bryan and George you guys rock. I read somewhere on this forum that the Navy back in "the day" used to overfill their tanks. I know I read it here and it was from someone that has been around. I let that nugget stick in my head. Great conversation and as usual I learn even more!
"Where'd ya get that ol' thang, don't cha' know them thare things ill kill ya!"

Live From the Red Sea,

Russ

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