What Is a Damper and How Do They Work?

Dampers are well known components that are utilised in many systems, especially suspension systems. However, what is a damper and how do they work? In this blog, we aim to answer these questions and provide a full understanding of the component.

What Is a Damper?

A damper is a mechanical device (or hydraulic) that absorb and damp shocks impulses. Generally, dampers are hydraulic devices that use oil as the working fluid to damp shocks. The thermal energy created is dissipated through the oil and to the surrounding housing – a primary process to help a damper work efficiently.

The design of dampers helps accommodate a range of forces and hence are available in linear, rotary and eddy current versions. However, linear dampers are the most widely used damper, so they are the ones we will cover in this article.

Why Are Dampers Used?

Dampers are commonly used on vehicles ranging from rail to road as part of the suspension system. Dampers improve ride comfort and quality for the passengers. Without dampers, there would be a continuous oscillatory motion every time a bump or shock occurs. Slight vibrations and sudden movements remain in cars and trains, however, they are reduced by dampers.

In addition, to ride comfort, dampers also reduce shocks on the vehicle frames, which help extend their life. If the forces experienced on the vehicle aren’t minimised, the stress in the structure will increase, reducing its life. A benefit of this is reduced maintenance costs and better reliability.

In rail vehicles, dampers connect the bogie to the car body, damping their relative movement and forces. The dampers take the form of lateral and yaw dampers to damp their respective forces in their axis. Additionally, a bogie has a primary damper that damps vertical forces – an important axis for ride comfort.

How Does A Damper Work?

A damper works by converting kinetic energy into thermal energy. Shocks and irregularities in surfaces provide vibrations and sudden movements, which are the source of kinetic energy.

The most common design of a damper is a twin-tube design. A linear twin-tube damper consists of a primary pressure tube and a reserve tube. Dampers contain a working fluid, a type of oil that will change depending on the desired level of damping and heat dissipation – a more viscous fluid will require a greater force to compress.

Valves act as the primary source of fluid passage, triggered by internal pressures in the fluid from compressive and rebound forces. The valves tend to be located on the piston head and at the bottom of the pressure tube.

As the piston moves down in the pressure tube, the fluid is compressed. The pressure of the fluid opens the valves in the piston head and at the bottom of the working fluid, allowing fluid flow. As the fluid is pressurised and forced through the valves, heat energy is generated, which is then dissipated.

During the extension phase (rebound), the piston head travels upwards through the pressure tube. The upward movement creates a partial vacuum in the pressure tube resulting in a suction force on the fluid, which forces open the valves at the bottom of the pressure tube, allowing fluid in from the reserve tube.

The valve make-up in the damper controls the compression and rebound characteristics of the damper. For example, the compression portion of the motion can be made ‘softer’ and the rebound portion ‘stiffer’ by manipulating the valve makeup.

During testing, it is common to adjust the valves to obtain the desired characteristics. Springs control the pressure required to open/close the valves, and this can be altered by tightening/untightening screws on the springs.

Different Types Of Dampers

There are three types of dampers – Linear, Rotary and Eddy Current. Linear and rotary dampers are the two most popular types of dampers with limited uses for eddy current dampers.

A linear damper is the most common and, as the name suggests, operates in a linear fashion damping forces in one axis.

A twin tube is a popular type of damper — Monotube and twin tube dampers

Rotary dampers contain two subcategories of dampers – vane dampers and continuous dampers. Similar to linear dampers, rotary dampers will damp forces, however, this time, it is torque that is damped.

Eddy current dampers utilise a large magnet inside the damper to provide resistive forces. Unlike the other types of dampers, eddy current dampers are a frictionless system.

What Is in A Damper?

A Damper consists of many different components, which all contribute to the characteristics of the damper.

Dust Cover – A dust cover is the top half of the casing, which acts as a barrier to the piston shaft and ensure it is not easily contaminated. The dust cover travels over the reserve tube during operation.

Guide Ring – A guide ring is fitted to the circumference of the reserve tube and acts as a guide for the dust to ensure it squarely travels over the reserve tube.

Pressure Tube – The pressure tube holds the bulk (or all) of the hydraulics and is the tube in which the piston operates.

Piston – The piston is made up of the piston head and the piston shaft. The piston head has seals around its circumference to help create a tight fit between itself and the pressure tube – helping control the flow passage of the oil. The piston head also contains valves and oil passages.

Valves – There are several valves in a damper. As mentioned above, valves are commonly present in the piston head to help control oil flow. Additionally, there is also sometimes a valve arrangement at the bottom of the pressure tube if a twin-tube set-up is used to control the oil flow between it and the reserve tube.

Compensating Chamber – The compensating chamber is the void present between the pressure tube and the reserve tube.

Gas Bags – Gasbags are used in the compensating chamber and are filled with compressible gas. One of the purposes of the gasbags is to act as a spacer between the pressure tube and reserve tube to maintain a constant distance allowing repeatable fluid flow. The gasbags also act as a compensator for the difference in oil levels between the two tubes.

Summary

A Damper is a central component in suspension systems and work by damping forces experienced. The valves in the damper work by controlling the passage of fluid to manipulate the desired characteristics.

There is a range of dampers available for different forces experienced e.g. rotary, however, a twin-tube linear damper is the most common damper used in industry. The components in a damper all play their part in ensuring that it operates efficiently and effectively.

After reading this post, hopefully, you have a good understanding of a damper, how they work and what they consist of.