Do compressed air tanks float?

You may be wondering do empty scuba tanks float? The answer depends on what the scuba dive tank is made from. You may also be wondering what difference this makes when you’re scuba diving; this I will explain in this article.

Do empty scuba tanks float - This depends on the material they are made from

Quick answer to the question do empty scuba tanks float: Empty steel tanks don't float but are less negatively buoyant. Whereas aluminium dive tanks float when they are empty or at the point of reserve air.


Do empty scuba tanks float?

Whether or not an empty scuba tank floats is down to the material its made from. There are two main types of dive cylinder, which are steel and aluminium tanks.

One of these floats when empty, whereas the other doesn't.

More Reading: What are scuba tanks made out of (Steel vs aluminium scuba tanks)

Do empty steel dive tanks float?

A dive cylinder made from steel is negatively buoyant when full. But a steel tank is also negatively buoyant when empty, which means it does float when empty.

However, when a steel cylinder is empty, it is less negatively buoyant than a steel tank which is full with compressed air.

The amount of buoyancy of dive tanks is important for scuba divers when trying to maintain neutral buoyancy.

As you consume the air in your dive tank during the course of a dive, the tank reduces in negative buoyancy. That means at the end of the dive you'll need slightly more weight than you will at the start of the dive to remain neutrally buoyant.

More Reading: How To Achieve Neutral Buoyancy Scuba Diving (Made Easy)

Do empty aluminium dive tanks float?

A dive cylinder made from aluminium is negatively buoyant when full. But an aluminium dive tank is positively buoyant when empty (see video below); i.e. an empty aluminium tank floats.

When I say empty, what I actually mean is when the tank has its reserve air remaining in the tank at the end of a dive.

The amount of reserve air recommended in the United States is 500psi, which in the UK is measured in BAR, and is 50 BAR. This means that an aluminium dive tank with 500 psi or 50 BAR will float in water.

This change from negative buoyancy to positive buoyancy during the dive will impact your overall neutral buoyancy.

This means that at the end of the dive if your dive tank is made from aluminium will increase your buoyancy. Which means you'll need more weight at the end of your dive to compensate for this added buoyancy. But of course you need to add this weight at the beginning of your dive before your descent.

Scuba tank buoyancy the difference between a full cylinder and an empty cylinder

Below is a great video showing the difference in buoyancy between an empty dive tank made from aluminium vs an aluminium dive tank that's full of compressed air (or actually in the video the aluminium cylinder has its reserve air of 500psi or 50 BAR).

I hope you enjoyed this article about do empty scuba tanks float

I’d love to hear from you. Tell us about your adventures of diving and snorkeling, in the comments below. Please also share your photos. Either from your underwater cameras or videos from your waterproof Gopro’s!

If this article hasn’t answered all of your questions. If you have more questions either about snorkeling or scuba diving (or specifically about do empty scuba tanks float), please comment below with your questions.

There will also be many more articles about scuba diving (and snorkeling) for you to read and learn about these fabulous sports.

Have fun and be safe!


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