What Are Expansion Bellows and How Are They Useful?

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At Inflex Hydraulics, we have been at the top of the hydraulics industry since 25+ years, focusing on high-quality fluid power solutions. All our experience has made Inflex Hydraulics become a household name in a number of industries, known for our quality and persistence. In today’s blog post, we dive into one of our most renowned components in piping systems; expansion bellows.

What Is An Expansion Bellow?

Expansion bellows are also known as metal expansion bellow joints, which – as their names suggest – help in the contraction and expansion of piping systems caused by temperature fluctuations. As pipelines face extreme temperatures, they either expand or contract, depending on how high or low the temperature gets. This is where the expansion bellow joints come in. Without expansion bellow joints, the pipelines would face extreme stress and risk bursting because of pressure buildup, however, a good quality expansion bellow joint can easily manage thermal expansion while reducing the risk of failures.

Expansion bellow joints also help with issues such as vibrations, pressure surges, and irregular movements caused by other mechanical components, making them an all-in-one component to secure pipelines with and maintain their integrity and functionality.

How Do Expansion Bellows Work?

Expansion bellow joints are flexible connectors that help with thermal expansion, vibrations, and abnormal mechanical movements in pipelines, vessels, and machinery. These bellows are made from durable materials such as stainless steel and nickel alloys, which are great at withstanding high pressures as well as temperatures.

The primary component within a bellow is the bellows element, which compresses to accommodate the expansion of pipelines and reduce stress. Conversely, as the temperatures drop, the bellow expands to compensate for the pressure buildup, thus maintaining the structural integrity of the piping system.

Types of Expansion Bellows

There are many types of expansion bellows, each designed with its unique properties and applications. So, without further ado, let’s dive in:

Axial Expansion Bellows

Axial expansion bellows are adept at handling longitudinal movements in piping systems. The axial expansion bellows increase or decrease their length to accommodate the changes in the pipe’s length due to thermal expansion. Without these bellows, the thermal expansion or contraction would put tremendous pressure on the piping systems, putting them at risk of bursting or leaking.

Tie Rod Expansion Bellows

Tie rods are the rods or bars attached to the expansion joint assembly. The sole function of the Tie Rods is to handle and continuously restrain the full bellows pressure thrust during normal operation while allowing only lateral deflection. Whereas, angular rotation is only possible if two tie rods are used and placed 90 degrees opposite to the direction of rotation.

Pipe Expansion Bellows

Pipe expansion bellows can be found in large-scale industrial workings where piping systems carry hot fluids, steam, and exhaust gases. They are made from sturdier material that can support the thermal fluctuations without damaging the pipes or the system.

Engine Exhaust Expansion Bellows

Engine exhaust expansion bellows help manage the thermal expansion caused by exhaust systems in engines. These types of bellows are located near the engine and are subjected to extreme temperatures, vibrations, and movements; thus they need to be extremely flexible and durable in order to withstand the harsh conditions of a vessel’s/ships engine. The main purpose is to protect the adjacent pipes and machinery from extreme temperatures and ensure the smooth operation of the engine.

Stainless Steel Expansion Bellows

Stainless steel expansion bellow joints are more common and can be found in regular housing units. These bellows help piping and duct systems to mitigate the effects of movement, stress, and temperature fluctuations. Stainless steel expansion bellows are made from high-grade stainless steel and nickel alloys that offer above-average resistance to corrosion, ensuring longevity and durability for years on end.

Single Expansion Bellows

Single expansion bellows are designed to absorb all the movements of the piping system – where they are installed. These bellows come with end connections such as flanges, pipe thread etc.

Universal Expansion Bellows

Universal expansion bellow joints are flexible piping components. They are adept at absorbing movement in multiple directions within a piping system. These bellows work in a way that they can accommodate different movements such as axial movement, lateral movement, and even angular rotation. Universal expansion joints typically consist of two corrugated bellows connected by a central pipe spool or section.

Hinged Expansion Bellows

Hinged expansion bellows are designed to absorb angular movement in one plane only. This means they can handle bending or twisting of the pipe in a single direction. Hinged expansion joints consist of a single bellows with hinges attached at both ends. These bellows are limited to handle one side movement only. They do not accommodate axial or lateral movement. 

Gimbal Expansion Bellows

The gimbal expansion bellows utilize a unique mechanism called a gimbal ring. This ring has two sets of hinge pins or pivots perpendicular to each other. This allows multi-directional angular movement and helps the bellows to tilt and swivel freely. Gimbal expansion joints are designed to absorb angular movement in multiple planes. This means they can handle bending or twisting of the pipe in any direction.

Pressure Balanced Expansion Bellows

Pressure balanced expansion bellows are a specialized type of expansion joint designed to address a key challenge of pressure thrust in piping systems. They are adept in maintaining pressure thrust created by internal pressure pushing on the bellows in a conventional expansion joint. Pressure balanced expansion bellows absorb axial movement caused by temperature changes while counteracting the pressure thrust.

Externally Pressurized Expansion Bellows

Externally pressurized expansion bellows offer a unique solution for accommodating large axial movements in piping systems, especially when dealing with high pressure. They achieve this by utilizing external pressure to counteract the internal pressure pushing on the bellows. Externally pressurized expansion joints are ideal for situations requiring large axial movements that standard expansion joints might struggle with.

Rectangular Expansion Bellows

Rectangular expansion bellows are specifically designed for rectangular air ducts in HVAC systems. They address thermal expansion and contraction within the duct by utilizing flexible metal sheets formed into convolutions. Their primary function is accommodating axial movement caused by temperature changes within the duct system.

Thick Wall Expansion Bellows

Thick wall expansion bellows are a robust type of expansion joint designed for large-diameter piping systems and applications with high pressure. They are a reliable choice for applications where standard expansion joints might not work due to pressure limitations.

The Perks of High-Quality Expansion Bellows

Expansion bellows play a crucial role in ensuring the smooth operation of piping systems. Here are some key reasons why they are essential:

  1. Mitigating Thermal Expansion Stresses

Thermal expansion causes significant stress on piping systems and increases the chances of leaks. These stresses can also lead to bending, joint failures, and even system breakdowns that can prove to be costly to repair. Expansion bellows compensate for the temperature fluctuations and reduce the risk of damage.

  1. Reducing Vibrations and Pressure Surges

Machines – when operating – cause vibrations and pressure surges within piping systems. By absorbing these vibrations, bellows protect the attached equipment such as pumps, and turbines from potential damage.

  1. Space and Cost Efficiency

The closest alternatives to expansion bellows are pipe bends and loops which offer lesser absorption capabilities and take up more space. The efficient design of the expansion bellows removes the need for additional external support and anchor points, making them a cost-friendlier version of its alternatives.

Uses of Expansion Bellows

Expansion bellows are used in a wide range of applications across various industries. Some common applications include:

Pump Suction and Delivery

For pumping systems, expansion bellows are installed at the suction and delivery points to account for the vibrations and movements caused by the pump. This maintains the integrity of the piping system and prevents any damage coming to the pump or its connected components.

Diesel Engine Exhaust and Air Intake

When it comes to diesel engines, expansion bellows are used in the air systems as well as the exhaust systems to accommodate for thermal expansion and vibrations. This improves the efficiency of the engine, while ensure that no connected components are damaged.

Fire Safety and Hot Water Systems

One of the most common applications of expansion bellows is in fire safety and hot water systems that need to be managed on a regular basis. The expansion and contraction caused by these systems puts stress on the pipes which can lead to leaks.


Expansion bellows are one of the most critical components of piping systems, which provide flexibility, reliability, and security to pipes. The different types of expansion bellows are meant to counter various different problems posed by thermal expansion, pressure buildups, and vibrations.

Whether it is rubber expansion bellows, stainless steel expansion bellows, or metal bellows expansion joints, you must be able to identify which bellow type can cater to your needs the best while reducing the risk of damage.


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