How Bolt Tensioning Works

Bolt Tensioning essentially provides a hydraulic load, which acts directly upon the stud bolt.  This hydraulic load, commonly called the applied load, is calculated to cause the stud bolt to retain its specified residual load, when the hydraulic pressure in the tensioner is released.

High pressure oil from a small air operated pump acts upon the ram in the hydraulic head developing an axial force, which is transmitted directly to the bolt by the puller.

This force stretches the bolt and the extension is retained by tightening down the nut by simply turning the socket with a tommy bar.

Known pressure areas of the hydraulic tools ensures direct correlation between the pump pressure gauge reading and the applied load.

It is important to understand exactly what happens when nuts and bolts are tightened.

Apart from some compression of the gasket or joint material the flange is considered to be incompressible.

As a load is applied to a bolt the effect is similar to the stretching of a spring, the studbolt will elongate.

This elongation or spring effect of the bolt is what maintains the load in the joint and the gasket compression.  To maintain uniform gasket compression it is essential therefore that all stud bolts in any one joint have the same elongation.

The Bolt Tensioner can be applied to a single bolt, or any number of bolts, depending upon access and application.

However,  to give the most accurate residual bolt loading and uniform compression of a joint, the tools are ideally applied in an arrangement where all the bolts can be simultaneously tensioned.  In a gasketed flange, a minimum of 50% of the bolts should be tensioned simultaneously.

100% tensioning is achieved where tensioning tools are attached to bolts alternatively on each side of the flange.  100% tensioning combines the greatest accuracy with the shortest assembly times.

Hydraulic hoses connect all of the tools to the air driven hydraulic pump unit enabling every bolt to be tensioned simultaneously.

This ensures that:

• The gasket is compressed evenly throughout the operation.
• All bolts have the same accurate residual bolt load.