How Does a Pressure Vessel Work?

In numerous industrial applications, from manufacturing to energy, the utilization of pressure vessels is paramount. The pressure vessels play a vital role in many industries. They are used for containing fluids and gasses at certain pressures. But how does a pressure vessel work exactly? 

Understanding the working principle of pressure vessels is just as important for you as it is for us as manufacturers. We will use our deep knowledge and vast experience to explain what pressure vessels are, how they work, what their main components are, and the most common applications. As a bonus, we added some handy maintenance tips at the end.

What Is Considered a Pressure Vessel?

Pressure vessels are specially designed containers whose purpose is to contain liquids, vapors, and gasses under pressure that is different from ambient pressure. According to OSHA, pressure vessels are typically designed to operate at pressures above 15 PSI. In such cases, the American Society of Mechanical Engineers (ASME) provides guidance on the fabrication and operation of these pressurized storage tanks.

As pressure vessel manufacturers, we must take into consideration a range of factors when designing a tank for a client. These include any internal and external pressure requirements, the design and operating temperatures of the vessel, the weight of the vessel when full, how the tank will be supported, and other things. 

It is crucial that our customers understand their requirements and specifications so that their pressure vessels can be adequately designed for their particular applications.

What Is Considered a Pressure Vessel?

How Does a Pressure Vessel Work?

The pressure vessel working principle centers around reaching the required pressure level. There are different ways of delivering pressure.  Since pressure vessels are mainly designed to hold fluids and gas under pressure, the pressure can be delivered directly to the vessel by supplying pressurized liquids or gasses through nozzles and valves. 

Pressure can also naturally build up inside the vessel when heat is applied to its contents while the vessel remains sealed.

Finally, pressure vessels may experience external pressure, such as a vacuum, when they are being emptied or when the contents inside the tank cool rapidly, leading to condensation.

Understanding how pressure vessels work is essential for both us as manufacturers and you as a user of the vessel. During the designing and manufacturing process, we take into consideration the pressure and temperature requirements, the mass or weight of the contents, how the vessel will be supported, as well as any loads that will be acting on the tank.  Using these inputs, we perform calculations that guide us in determining the design and thickness of each component.

How Does a Pressure Vessel Work

Components of a Pressure Vessel

To fully understand how does a pressure vessel work, you must get familiar with its components. Every pressure vessel has a shell, heads, nozzle, and supports. In addition, pressure vessels can have other attachments corresponding to the requirements of the particular application.


The shell has one of the most important roles in the pressure vessel system, which is containing the pressure. Generally, the shell has plates that are rolled into cylinders and welded together. The thickness of the plates is extremely important and calculated so it can maintain the vessel pressure.

The shells of the pressure vessel can be found in different shapes. However, in our experience, the most commonly used are round shapes, including spheres, cylinders, and conical. The reason why we prefer the round-shaped shells is because that is an efficient shape for holding internal pressure.

Pressure vessel shells can be made of different metals, such as:

  • Stainless steel
  • Carbon steel 
  • Monel
  • Alloy 20
  • Inconel
  • Hastelloy


The purpose of the head is to close the end of the pressure vessel playing a sealing role. In most cases they are welded directly to the shell, but they can also be equipped with a flange that can be bolted to a mating flange that has been welded to the shell. This configuration enables the head to be removed for access or cleaning.  

Just like the shells, they come in various shapes and sizes. They can be either curved (dished), conical, or even flat. Dished heads are the most common, and are usually the most cost-effective. 

Going into detail, pressure vessel heads are available as:

  1. Flatheads are suitable for vessels with smaller diameters and environments with low-pressure requirements.
  2. Dished heads have a straight flange at the base and semi-hemispherical domes with a knuckle. They are further divided into several subcategories depending on their radius:
    • ASME F&D head
    • Elliptical heads have a deeper dish with better pressure retaining geometry than ASME F&D heads, but are taller than F&D heads, making them less appropriate for areas with low ceiling heights.
  3. Conical heads have a wide base, a tapered head, and a concentric cone shape


The nozzles allow the fluid or gas to enter and exit the pressure vessel. Because nozzles penetrate the pressure boundary of the vessel, they weaken the tank’s structure. Therefore, nozzles must be designed with enough reinforcement to offset the loss in strength that comes from creating an opening in the tank.


The pressure vessel requires different kinds of supporting hardware for proper function. They are designed to take the weight off the pressure vessel.

Supports have the responsibility of bearing the weight of the tank or pressure vessel.  Vertical vessels can be supported by legs, side supports, or skirts. Legs and skirts are used for ground support, while side supports are used when the tank will be suspended off the ground. Horizontal vessels are supported by saddles.

Pressure vessel manufacturers must perform detailed calculations to make sure that the tank’s supports are properly designed.  Again, these calculations must consider not only the tank’s size, shape, weight, and material of construction, but also any external loads that may be applied to the tank as well as the wind and seismic conditions at the job site.

Applications of Pressure Vessels

Considering the types of pressure vessels available, we have clients coming from many different industries. Common businesses that contact us for pressure vessels come from the chemical, paper, energy, and industrial manufacturing industries.

Tips for Maintaining Pressure Vessels

To contribute to the proper work of pressure vessels, you must maintain them correctly. Some expert tips on how to keep your pressure vessels in top shape are as follows:

  • Hire professionals to do thorough internal and external inspections at regular intervals to detect any defects
  • Replace parts when needed
  • Do periodic pressure tests such as hydrostatic, pneumatic, leak, and mechanical integrity tests
  • Maintain cleanliness and hygiene within and outside of the pressure vessel
Tips for Maintaining Pressure Vessels


Pressure vessels are pieces of industrial equipment that store or process liquids and gases under pressure. They have a broad range of uses that play an important role in manufacturing the goods we use every day.  Understanding how does a pressure vessel work is significantly important. So, if your organization needs tanks or pressure vessels, please contact us and request a quote.

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David Onachilla

David is the owner of Savannah Tank and brings a wealth of knowledge in the tank manufacturing industry to our readers.

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