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Difference Between Pressure Vessels, Tanks, and DOT Cylinders

There are many subcategories of vessels used to hold liquids like DOT cylinders, tanks, and pressure vessels. They each have their own distinctions and uses. This article will help you figure out what type of vessel you need and what they’re commonly used for.

What is a tank?

“Tank” in a storage context usually means a metal or plastic container used to store liquids for short to long periods of time at atmospheric pressure and temperature. They can range in size from only a few gallons to entire reservoirs, although most fall somewhere in between.

Tanks are used to store things like:

  • Water
  • Oil
  • Gasoline
  • Diesel
  • Other chemicals

The material a tank is made from will depend on the contents it’s designed to store. Some liquids react with certain metals, so a different metal, plastic, or concrete might be more appropriate to use as a material. Steel is the most common material used for larger tanks since it’s strong, relatively inexpensive, plentiful, and malleable. Plastics are often used when the tank is smaller since many plastics are cheaper and lighter than steel.

What is a DOT cylinder?

A DOT cylinder is used to store and transport liquids, usually pressurized gases. They have to meet the requirements set out by the Department of Transportation and pass inspection in order to be qualified for use. This is because pressurized gases have additional hazards that need to be mitigated in order to safely transport them.

Some gases that are often stored in DOT cylinders include:

  • Nitrogen
  • Oxygen
  • Helium
  • Argon
  • Air

In order to efficiently transport gases, it makes sense to compress the gas as much as possible. This is done by either drastically lowering the temperature of the vessel the gas is stored in, or more commonly, by raising the pressure by pumping a lot of a gas into the confined volume.

What is a pressure vessel?

Pressure vessels are tanks specifically designed to contain pressurized liquids, much like DOT cylinders, but pressure vessels are generally designed to be used where they are located instead of making cross-country trips. They have particular design requirements that have to be met in order to safely hold their contents. Many pressure vessels are designed according to ASME standards, which are the standards used worldwide for vessel and boiler design across industries.

Some applications for pressure vessels are:

  • Research and technology development
  • Cryogenic cooling
  • Manufacturing
  • Spacecraft testing and assembly
  • Diagnostic equipment

Learn more

At Rexarc, we specialize in designing and manufacturing custom steel pressure vessels for our customers, and we’re happy to answer questions you might have about tanks, cylinders and vessels! Reach out to us if you’d like to talk to an expert or aren’t sure where to find the information you need.



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