A Complete Diving Cylinder Buying and Maintenance Guide

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Beware: You should never explore wild caves alone or without proper gear. Consider getting in touch with a Grotto of the National Speleological Society at www.caves.org or a qualified cave club. These groups are skilled and will train you. Without sufficient knowledge, preparation, and equipment, cave exploring can lead to serious injury or death.

When buying your first diving cylinder, you might ask “Are all diving tanks the same?” The answer is no. To the untrained eye, they look the same, but small differences in the features can decide whether they are safe for you and sufficient for your specific needs or not. Therefore, you have to be extremely careful while comparing diving tanks, especially online.

Even if you are newly certified and think you know everything there is to know about caving equipment, it is pertinent to be extra careful when it comes to buying the tank. Once you’re underwater, your life mainly depends on this.

But we’ve laid out some of the frequently asked questions about diving tanks by both professional and recreational divers. After reading our buying guide below, you will understand what is happening in the diving world, and easily make the correct choice.

Two divers with dual diving cylinders on their backs study something underwater.
If you plan on staying underwater long, you might opt for a dual tank setup like these people.

What is a Diving Cylinder or Diving Tank?

Before you can even understand the difference in diving tanks and their features, you need to know what a diving tank is. Knowing the essentials of a diving tank will help you understand why many variations of this product exist. It will also shed light on which product is better for cave diving specifically.

A diving tank, also known as a ‘diving cylinder’ or ‘scuba tank’, is filled with compressed, purified air. These tanks usually have 20.9% percent oxygen – not 100% as people often assume. Pure oxygen becomes dangerous when you are deeper than 20 feet, quite normal depth for a cave diver. Breathing 100% oxygen at this depth leads to central nervous system oxygen toxicity, which is deadly.

By taking in pure oxygen, fluid starts accumulating in the lungs, chest pain occurs, and you begin to cough. Couple this with being underwater and you have a recipe for disaster, and even loss of life. On the contrary, when nitrogen enters our body it improves brain function and assists the immune system. While oxygen is necessary for life, our natural environment provides us with a mixture of gases, and so every diving tank does as well.

Although there is a presence of nitrogen, argon, carbon dioxide, methane, neon, and helium, the majority of the air in the tank is nitrogen. For ease of calculation and understanding, it’s roughly 78% nitrogen and 21% oxygen. Our natural air has these same measurements, with primarily argon making up the remaining 1%. This mixture of gases in the diving tank makes breathing underwater feel like taking a normal breath.

View from above of a scuba diver with two side mount diving cylinders.
That Jaws music doesn’t work the same when you’re looking from above, does it?

Can anyone buy a Diving Cylinder?

Anyone can buy a diving tank without being certified. With that said though, some reputable dive shops may ask to see your diving certificate before selling their equipment. This dangerous hobby requires proper knowledge and practice. If you don’t have a diving certificate, they will ask to know more about the sort of dive project you are involved in so they can recommend the right products.

Unfortunately, there isn’t any upper or lower age limit set for divers. We believe no one should sell a diving tank to minors, often being unfit or not competent to dive safely. Teenagers often take risks to impress their friends, especially in today’s social medial world, and going diving without proper guidance will only put lives at risk.

Consider getting certified first. You can then dive anywhere you want to in the world. When you take the diving course, they teach you about correct use of different diving tanks and other equipment. Completion of the course will allow you to buy any diving tank you want and dive without an instructor, and it is highly recommended for any enthusiast.

Which Cylinder or Tank do you need?

To further understand the qualities of a good diving tank before you make a decision, you need to consider things like air capacity, material used, valve fittings, and more. You should also determine what your needs are before you ever go cave diving.

Is it a one-time diving trip? Or are you going to dive over and over again in various diving destinations? More than 90% of divers are novices or dive just for recreational purposes. If it is only a one-time dive, to have some fun with your friends or significant other, you don’t necessarily need to buy a diving tank. The most famous diving spots usually have stores near them that provide all the diving equipment on rent. Their products are thoroughly tested and give the best performance.

However, if you dive quite frequently and visit more unknown locations, getting your personal diving cylinder is recommended.

A diver sports two diving cylinders, one on each side.

1) Capacity

The capacity of the tank is all about how much gas you will get.

It is directly related to the size of the tank as well. You will naturally lean toward the maximum capacity when planning to explore the depths of a water-filled cave. A physically larger tank contains more air and holds more pressure. But this doesn’t mean one should opt for the bigger tank only. A larger cylinder means more bulk and weight to keep with you. For a larger person, it is probably a good idea to go with a large tank that fits better on him. But for most people, an average-sized tank is sufficient, and can be professionally serviced by a local dive store or certified testing facility. So if you are around 6 feet, opt for a normal-sized cylinder.

The most common diving cylinder among experienced cave divers has 80 cubic feet of air capacity. It offers adequate bottom time for most divers.

But this size is not suitable for every diver. In case your diving is more like scuba diving and not actual cave diving, the 80 cubic feet air capacity cylinder can be uncomfortably tall for you. You won’t need nearly that much, as you will typically be in more shallow water and for much less time. For shallow water, a cylinder with 63 cubic feet air capacity is a good choice.

This means you should always have an idea about the depth of the water cave you plan to visit. Knowing how much capacity you need before purchasing a tank will save a lot of time and help avoid unnecessary problems underwater. If you dive often and in different locations with different depths, an 11-liter aluminum cylinder with 80 cubic feet capacity is a great choice.

2) Valve Fittings

Valve fittings inside a diving tank also play a significant role.

They come in many types and have many components like a knob, o-ring, and burst disk. But they attach to your tank in only two ways – Yoke and DIN.

The Yoke fitting or attachment is famously known as the A-Clamp or International Fitting. It is often used in the aluminum 80 scuba tanks and fits over the top of their valve. The main benefit of Yoke Fitting is it is simplest to use; it is also affordable and more suitable for tanks with average pressure ratings.

On the other hand, we have DIN Fittings.

This fitting is used mostly outside the United States and it can survive higher maximum pressure (over 3000 psi). The DIN fitting is considered much safer than the Yoke fitting. Experts count on them for blending well with their high-pressure tanks.

3) Material

When it comes to the material, opinions vary on which is better.

Most cylinders come in either steel or aluminum. Both materials have their pros and cons. For example, the steel cylinders come in more variations and sizes. They also have substantially larger volumes inside and they are capable of holding 150 cubic feet of gas. Another benefit of a steel diving cylinder is the same wall thickness everywhere. This gives it great balance and makes it easy for the diver to dive in tight passages.

On the contrary, the design of the aluminum cylinder is a bit different. They are tail heavy as they have more metal at the bottom. They are also heavier and bulkier than the steel model. But the main benefit of an aluminum diving cylinder is it can’t rust. Even saltwater won’t cause any significant corrosion, so it is safe to dive in the ocean and explore sea caves.

Getting your Tank Inspected

One should inspect the quality of breathing air and the overall working of the diving tank at least once every 3 months, according to the industry standards. If the cylinder is emptied underwater, moisture can accumulate inside.A good company provides an internal visual inspection, and checks things like internal corrosion or valves fittings before refilling it.

When you have your own diving cylinder, any competent person at your local dive store can help inspect it. Depending on when your last inspection was, this step is vital. The diving cylinder is an unsung hero among all the diving equipment, and maintaining it correctly is crucial. A professional can help you by giving a visual inspection, taking off the valves to check them, looking inside the tank for corrosion, and more. Next, he will perform hydrostatic testing, according to the local laws and regulations. This testing is all about checking the capacity and flexibility level or firmness of the tank’s wall as your life depends on it, especially if it is filled more than its capacity. Lastly, he sees how well the tank is preventing water from entering it. Even 1% of moisture can cause contamination.

A man conducts a visual inspection of a diving cylinder.
If Louis CK ran a cave diving shop instead of being a comedian.

How to Deal with Diving Cylinder Issues Underwater

Though some diving cylinders work best in a specific kind of environment, such as in colder water (10 degrees Celsius), most diving cylinders work in all situations. But you might still encounter issues underwater, depending on how well your tank is maintained, or simply from bad luck.

For example, say your tank stops working properly during the dive. This is rare, especially if the tank is new or you are maintaining it regularly, but it can still happen. The best practice is to head back to the boat at once, rather than trying to check the tank underwater. If it’s hard to abort the dive immediately, give a signal to your teammate for the backup.

A good team will understand your signal and help you immediately, so you don’t run out of air. But bear in mind, you shouldn’t use your buddy’s equipment for long and continue to explore underwater. This endangers both of you and puts the safety of the tank in jeopardy due to the decompression of the air. Decompression in the diving tank causes physiological effects like loss of consciousness. Other symptoms include fatigue and muscle pain.

In other cases, you might spot blood in the mask. Blood during diving typically means you shouldn’t have been diving in the first place. But it isn’t due to the mixture of gases inside your diving tank. Instead, it might mean you have pressurized your sinuses too forcefully at that depth. Sometimes it can happen because of an allergic reaction, like an upper respiratory infection or dried mucus.

Luckily, while blood can be quite jarring to see while underwater, it’s not always a life-threatening situation. Still, it is better to abort the dive and consult a doctor right away, to be safest.


Buying the right diving tank is an important task, but maintaining the cylinder is also key for a successful trip.

Proper maintenance prevents failure and ensures you won’t be put in an emergency. Fortunately, it is easy to maintain both steel and aluminum diving tanks. After cave diving, rinse it with fresh water completely 2-3 times. This will prevent corrosion and clogging to the tank valves. 

In addition, make sure the tank has a little pressure – not a lot – when you are storing it because contamination builds up easily in an empty tank. On the other hand, a full tank could show surface cracks due to the pressure over time. Keeping light air pressure inside the tank keeps it safe and usable in the long run.

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