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How hydraulics work in Bolt Tensioning

In this article, we will cover the fundamentals of hydraulics, what components are included in a hydraulic system, and how bolting solutions use hydraulics with their tensioners.


The fundamentals of hydraulics

Hydraulics is a transfer of force through a liquid to move a mechanical object. The pressure is created via a power pack which, is exerted on a fluid in a small area. This pressure is transferred equally throughout the fluid, and although the pressure is the same when exerted over a large area, multiplies the force given the ability to move greater objects.

hydraulics car illustration

How do hydraulics work within Bolt Tensioning?

Throughout history there have been different variations of fluid used for this purpose, but for tensioners the fluid of choice is mineral oil. The reason that mineral oil is used is because of its lack of compressibility. This means the oil does not compress under load or pressure making it a stable medium for a tensioning system.


For tensioning a force is transferred from the power pack to the tensioner with the following components:-


  • Power pack - This creates the pressure and flow of oil to
  • Hoses - These are the connection between the power pack and the tensioner to allow the flow of oil and pressure transfer.
  • Tensioners - These create the force with the build-up of contained pressure
  • Hydraulic oil – This is the medium used to create the pressure and force.

Oil Characteristics

Oil has certain characteristics that we need to consider viscosity and temperature. The viscosity is the thickness of oil measured in centistokes CST.

The higher the value, the thicker the oil. The standard supplied is grade ISO 32 mineral oil. 32 centistokes are 40 degrees. Temperature can change depending upon the environment affecting the requirement. In extremely high temperatures a thick oil may be required over ISO 68 perhaps, conversely in extremely low temperatures, a thinner oil may be required for example ISO 22.

To summarize you should now have a basic understanding of the fundamentals of hydraulics, the equipment used within a hydraulic tensioning system and some important oil characteristics which should be considered. 

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