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Scuba Tanks: The Weight of Compressed Air (Empty Vs Full)

It is a recreational activity and also a professionally good sport. The scuba cylinder, otherwise known as a scuba tank, is an indispensable part of this sport because divers would not be able to breathe beneath the water without it.

You still cannot guess what sport we are talking about here?…..we mean scuba diving. The scuba tanks are quite heavy and weigh about 30 pounds. The weight even increases when the tank is filled. It can be discouraging to carry this weight on your back while swimming. 

But this should not scare you; the scuba tank weighs differently, and this is what you should consider when signing in for the sport? You might have been a scuba diver but have never bothered to know the weight of air you usually carry.

You might as well want to venture into scuba diving, but you feel reluctant because of the weight of the compressed is and cylinder you will be carrying. Do not worry if you fall in any of these categories.

Diving Or Scuba: Why Ditch the Tank...

This article brings knowledge about the weight of a scuba tank and the weight of compressed air. So what is the weight of compressed air? Read along to learn more.

What is the weight of an empty scuba tank?

The possible answer to this question cannot be straightforward. As you might know, scuba tanks are made of different materials; consequently, they will also weigh differently.

There are two major materials used in making scuba tanks; steel and aluminum. In addition, the size of the tank will also have a contribution to make concerning the weight.

Note: weight is the pull of gravity on an object and is proportional to its mass. Since this gravitational pull is fixed on earth, you can use weight and mass interchangeably.

The units of measurement can be newton, pounds, etc. But in this article, we will be using the pound. Please bear with us if you have to do some conversion for your understanding.

Steel scuba tanks

Generally, steel is a heavy material. The standard size of a scuba tank (80 cubic feet) made of steel usually weighs about 28 to 30 pounds.

However, when even talking about the weight of a scuba tank, we consider the dry weight (weight on land) and the wet weight (weight in water). So the 28-30 pound weight mentioned here is the dry weight. 

The steel scuba tank weighs slightly less than when on land in water, yet it is still negatively buoyant (buoyancy is the upward force exerted on an object by a liquid when submerged in it).

That means it will sink in water, whether full or empty. Some steel scuba tanks are made for younger persons and will weigh less than the standard size steel scuba tank.

Aluminum scuba tanks

Aluminum is a lighter and softer material when compared to steel. However, aluminum tanks weigh slightly more than steel tanks. Are you surprised! Follow us as we explain. A scuba tank is usually made so that its walls can withstand pressure. But aluminum material is soft, which won’t qualify it for a scuba tank. 

Therefore, the walls of a scuba tank made of aluminum are usually thicker (meaning more material) to withstand water pressure. This makes aluminum tanks heavier in water than steel tanks.

However, aluminum tanks are still positively buoyant and will become more so when the tank is empty. The weight of a standard-size aluminum scuba tank is just slightly above that of steel tanks, which is between 31 and 35 pounds. 

Does Compressed Air Have Weight?

 Air has got weight (though negligible), and so too is density. You might want to argue this, but it is a fact. This property even increases when the air becomes compressed. The air that you find in scuba tanks is compressed and weighs more.

So you may be wondering why to add more weight when the tank already weighs about 30 pounds. The truth is, the amount of air added is usually about 6 pounds. 

This added air makes the weight of air in the scuba tank about 1/5 the weight of the tank, which is nothing much to worry about.

But the difference in weight brought about by the compressed air affects buoyancy which has a major effect on scuba diving. So, therefore, air begins to have significant weight when compressed.

What is the weight of a full tank?

We have established the weights of an empty tank (both steel and aluminum). We have also established that air, when compressed, has a significant weight. Significant weight here means that weight that can be recorded by a scale balance (usually an electronic scale balance).

We needed to establish also establish the latter fact so it could help our understanding of this sub-topic. The air scuba divers usually carry in scuba tanks is compressed.

So then, what is the weight of a full standard tank?

A standard scuba tank has a volume that can contain compressed air of weight 6 pounds. To be more precise, the weight of air in a standard tank when full is exactly 5.9 pounds. This implies for:

– A full standard steel tank, the weight is between 34.9-35.9 pounds.

– A full standard aluminum tank, the weight is between 36.9-40.9 pounds.

However, smaller tanks, as mentioned in a previous paragraph, do exist and will have less weight, too as well.

Conclusion

Scuba divers who love this sport are not always intimidated by the weight of a full tank, whether steel or aluminum. They know that while beneath the water, the weight will drop and do so continuously as they use it up for breathing.

Whether a steel tank is full or empty, it will sink if left on its own in water, and this means negative buoyancy. But this is not so with aluminum tanks. An aluminum tank will sink when full-negative buoyancy. 

But as you use up the air inside the tank, it starts responding to buoyancy until when it is empty and released by the scuba diver, it rises and floats on water- positive buoyancy.

We have limited the information provided here to standard tanks because they are the scuba professionals’ most popular and most used.

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Written by Water Diversions

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