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Using the correct scuba diving cylinder is just as important to a diver's success and safety as how they configure their gear. A diver may go to an enormous effort to insure every hose, reel and accessory is exactly right only to 'drop the ball' by making the wrong cylinder choice.

The Scuba Doctor dive shop brings you scuba cylinders from the leading cylinder manufacturers in the world — Faber and Catalina — so you can not only get it done, but can get it done right.

No cylinder is perfect for every diver, or every diving situation. The Scuba Doctor offers the most complete selection of cylinders in the industry, allowing you to choose what is best for your unique needs.

All cylinders from The Scuba Doctor are suitable for nitrox service (i.e. up to 40% oxygen), visually inspected and shipped with a current hydrostatic date (except where indicated).

Australian Standards

In Australia, scuba Tanks must be tested every year (12 months). We always ship cylinders with a current hydro test date. Due to manufacturing and import cycles, the popular sizes of cylinders typically have a factory hydro date less than 12 months old. However less popular sizes of cylinders may have a factory hydro date up to 24 months old as these are manufactured and imported less frequently.

As per the Australian Standards, the cylinders and valves we sell are for Imperial 0.750-14 NPSM (3/4 NPS) neck threads, NOT Metric M25 neck threads, and the valves have overpressure relief devices (burst discs). (Cylinders with Metric M25 neck threads do not comply with Australian Standards.)

The Faber steel cylinders have ISO 9809-1 markings. The Catalina aluminium cylinders have DOT-3AL2957 markings. All of these cyliners comply with Australian Standrads and are suitable for use in Australia. They may, or may not, meet the standards applicable in other coutries.

Choosing Your Scuba Cylinder/Tank

Scuba diving cylinders (USA: tanks, UK: bottles) are awkward and heavy, and if you fall down with one on you'll be lying on your back flailing your arms and legs in the air like a turtle flipped on it's shell.

Without scuba cylinders you can never be like that same turtle 'flying' gracefully through the water, experiencing a world that almost defies explanation.

Like all scuba gear, choosing a scuba diving cylinder/tank/bottle takes more thought and planning than just walking into a dive shop and grabbing the first thing you see.

There are a few different kinds of cylinders, each with their own pros and cons. Plus, not all diving cylinders can be used for all types of diving. The video below may help you to chose which dive cylinder is best for your needs.

Types of Scuba Diving Cylinders

Steel Scuba Cylinders

Steel scuba cylinders have been around since the start of scuba diving, while aluminium diving cylinders came into use in the 1970s. Steel scuba cylinders are typically more expensive than the same capacity aluminium cylinders.

A steel diving cylinder is a lot tougher than an aluminium one, making it less likely to pit or dent. If properly cared for it will last longer than an aluminium cylinder. However, steel rusts with exposure to moisture and thus needs more careful care.

Because steel is stronger it can be handle higher pressures with a thinner wall thickness, making a steel cylinder smaller and lighter than an aluminium one of similar capacity.

Also If you want to use higher pressures (e.g. 300 bar), you will need to use a DIN valve which may make it hard to get refills depending on where you're diving.

Most technical divers use steel scuba cylinders, but they can be a good cylinder for regular recreational scuba diving too. The most common size is a 232 bar, standard 12.2 litre steel cylinder, but many women and those who use less air often prefer a lighter and smaller 10.5 litre cylinder.

Steel cylinders are more negatively buoyant than equivalent aluminium cylinders and only become less negatively buoyant as they are emptied. Thus they are popular in cold/temperate water areas where thick wetsuits and drysuits are used, because a steel cylinder means you can carry less weight on your weight belt.

Aluminium Scuba Cylinders

Aluminium scuba cylinders came into use in the 1970s and are the most common scuba cylinders you'll find in tropical waters for recreational diving. Many dive shop, boat and resort operations use them worldwide.

The most common size used for diving is the aluminium 80 cubic foot (11.1 litre), but they can be smaller or larger depending on what they're meant to be used for.

For example, a bail out or pony bottle is much smaller than a standard size aluminium 80.

Aluminium cylinders being made of a softer, lighter material have thicker walls, making them larger and heavier than steel cylinders of the same capacity. Aluminium cylinders are relatively inexpensive and thus a good choice for most recreational scuba divers.

One downside of the aluminium scuba diving cylinders is that most go from being negatively buoyant to positively buoyant as they empty during the dive, so most divers wear a few extra kilograms (or pounds) of weight to compensate for this. There are a few models of aluminium cylinders that are built specifically to eliminate this problem, but like everything else, the more features it has, the more expensive it is.

Typically aluminium cylinders are certified for use at a working pressure of 200 to 210 bar. But some newer ones are available rated to nearly 230 bar. Again, these cylinders are more expensive and heavier.

Things To Consider When Buying Scuba Diving Cylinders

Here are a few other things to consider before buying.

  • Length/height of the cylinder. Is it so long it bumps your butt and the back of your head at the same time?
  • Weight of the cylinder. Is it too heavy for you to handle comfortably?
  • Type of diving. Do you technical dive or not?
  • If it's steel, is it a low pressure (LP) steel cylinder (e.g. 232 bar), or a high pressure (HP) one (e.g. 300 bar)?
  • Does it have a DIN valve, or more common A-clamp/Yoke valve, or a valve that can be converted from DIN to Yoke using an insert?
  • If it's a used cylinder, when was it last visually inspected or hydro tested?

Our Recommendations

When purchasing scuba cylinders, the long-term advantages of steel's excellent buoyancy characteristics and long life make it the best choice for most divers, but especially those in cold and temperate waters. Choose a 232 bar steel tank size that meets your needs when it is under filled, putting an end to short fill concerns. For most divers this will be a 12.2 litre (100 cubic foot) cylinder, but some may prefer the smaller 10.5 litre (85 cubic foot) cylinder.

If your budget is tight, then aluminium cylinders initially costs significantly less. If going with an aluminium cylinder, avoid paints, and choose the brushed finish.

For both steel and aluminium cylinders you should choose a convertible valve having a DIN outlet with K (yoke) insert, often described as a 'DIN/K' valve. (That's why we provide this as our standard offering.).

Remember, the standard 207 bar aluminium 11.1 litre (80 cubic foot) capacity cylinder with a K valve is not a "one-size-fits-all" tank. Making the right cylinder choice can significantly improve your diving enjoyment. Please use this list as a guide when reviewing scuba diving cylinders and you should be able to find the right cylinder/tank to last you for years of diving.

For more help buying the best diving cylinder (Tank / Bottle) for you, please see our Buying a Scuba Cylinder guide.

The Scuba Doctor dive shop is your best source for scuba diving cylinders.



Breathing Gas Quality

by Peter Fear, The Scuba Doctor,
first published in Dive Log Australasia, February 2006

How do you know what's going into your cylinder and what you are breathing meets the Australian Standard?

The average diver has probably never thought about it other than during their Open Water Course, when they may have learnt that the compressor inlet should be away from all exhaust fumes and your cylinders are filled with compressed air delivered via a filtration system and fill hose to your cylinder.

When you take your steel cylinder for its annual test and are told there was rust inside that had to be brushed and rumbled to remove at additional cost, did you wonder how it got rusty?

There are a several ways your cylinder can rust all of which, with simple care, can be prevented. I have found that the main cause of rust in cylinders is from moist air delivered into your cylinder from a Fill Station that has a poorly designed system, inadequate or poorly maintained filtration or a faulty compressor. Any of these can deliver moist air or other contaminants into your cylinder considerably decreasing its life expectancy.

Australian Standard 2299.1, 3.13 Breathing Gas Quality states in part:

Breathing air used in diving operations shall

  1. have no objectionable or nauseous odor;
  2. contain not more than (10 p.p.m. by volume) of carbon monoxide;
  3. contain not more than (480 p.p.m. by volume) of carbon dioxide;
  4. contain not more than (130 p.p.m. by volume) of water;
  5. contain not more than 1mg/m3 of oil;
  6. where supplied from a compressor, not be used for diving unless the compressor has, within the last six month period and every six months during operation, undergone a test to ensure that the compressed air satisfies the above requirements.

After operating an approved, Hydrostatic Cylinder Test Station for many years, I have seen cylinders contaminated with oil, water and other substances, some with excessive rust found during the cylinder's first annual test. Cylinders so rusted internally that removing the valves became difficult or when opening the valve to drain the cylinder, the odor of the air inside makes you nauseous. Some unaware divers are breathing contaminated air.

So how do you know what's in your cylinder? And for that matter how does your Fill Station know that the air they are filling your cylinder with meets the above standard?

Answer

AS 3848.2. Section 2.2.1 states in part:

Testing of the purity of compressed SCUBA air shall take place at least every three months or more often as appropriate to verify the performance of filters and driers.

A Breathing Air Test Kit can be used to quantitatively determine the content of the following in respirable air from compressors, filling systems and gas cylinders:

  1. Carbon Monoxide (CO)
  2. Carbon Dioxide (C02)
  3. Water Vapor (H20)
  4. Oil

The test kits are reasonably expensive and most Dive Shops do not own one, however Air Purity Tests are readily available for as little as $150.

When the tests are completed a Gas Purity Test Report is issued indicating the levels of contaminants, if they have passed or failed the standard and the date of test.

This report should be displayed at the Fill Panel for your satisfaction and verification.

Conclusion

Breathing contaminated air underwater under pressure, is not what we divers should have to think about. It is your right to demand as a minimum, air quality to the Australian Standard prescribed and the responsibility of all Filling Stations including University's and other Dive Clubs to supply and verify it. Accept nothing less?

Helpful Hints

If rust or other contaminants are found in your cylinder, question your Filling Stations. A chat with the Hydrostatic Test Station could help determine the cause.

The smell test will usually reveal odors from oil and some other gasses. This is done by holding your hand loosely over the valve, cracking the valve gently and smelling the expelled air.

Finishing a dive with an oily taste in your mouth is a dead give away for bad air.

Before filling your cylinder, aluminum or steel, crack the valve a couple of times to blow out any water that may have accumulated in the valve or it will enter the cylinder with the air fill. All experienced operators do this naturally.

Never bleed all the air from your cylinder.

Make sure you use a reputable Fill Station that proudly displays their current Gas Purity Test Report.

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