Pre-setting device PST

Bolt Tensioners PST Series

Pre-tensioning bolts with a bolt tensioner is a proven method in industrial bolting technology for absolutely precise and torsion-free tightening of high-strength bolted connections. Unlike conventional methods, the bolt is not rotated, but axially elongated.

Features and Workmanship:

• These tools are characterized by high pre-tensioning force, compact dimensions, and low weight.
• The pure tensile load prevents torsional stresses that are introduced into the bolted connection by rotating bolting methods.
• Series connection of several tensioning cylinders possible for even tightening of multiple bolts (e.g., in flange connections)
• Special steel alloy for longer service life.
• Tie rods made of high-strength special steel for maximum service life.
• Piston with maximum tensile force, even with device misalignment up to 2°. The pistons are equipped with stroke indicators.
• Cylinder made of high-strength special steel, optimized design for use in confined spaces. Corrosion-resistant due to hard chrome-plated surfaces.
• Bridge with wide access opening to easily reach the rotating sleeve for setting the nut.
• Rotating sleeve for setting the nut after pre-tensioning. Holes on the circumference allow the use of a turning bar.
• Coupling adapter - special couplings without the use of sealing rings or sealing tapes, thus leak-free and maintenance-friendly.
• Drip-free CEJN quick-release couplings for safe working. Two connections allow the series connection of several tensioning systems.
• Special seals for leak-free operation and easy replacement during maintenance.

Technical Data:

*Indicates the weight of the cylinder + adapter set of the respective size.

How the bolt tensioning cylinder works

The process of hydraulic bolt tensioning is divided into a few precisely controlled steps:

1. Placing the tool: The bolt tensioning cylinder is placed over the protruding threaded end of the bolt. A replaceable bush engages the bolt's thread.
2. Building hydraulic pressure: Hydraulic pressure is directed into the cylinder via a high-pressure pump. The piston of the tensioning cylinder moves upwards and axially elongates the bolt.
3. Securing the nut: Due to the elongation of the bolt, the nut slightly lifts off its base. The nut is then re-tightened by hand or mechanically onto the bearing surface without any effort, using an integrated rotary pin or a gear, until it is free of play.
4. Pressure release: The hydraulic pressure is released. The bolt attempts to contract back to its original shape. Since the nut is now firmly seated, the defined preload force is precisely maintained in the bolted connection.

Advantages: Tensioning bolts instead of turning them

Pure axial tensioning offers significant technical advantages for the safety and longevity of the connection compared to classic torque-controlled tightening.

No torsional stress in the bolt

When tightening a bolt under high torque, strong torsional forces (twisting) occur in the bolt. These superimposed stresses reduce the maximum load capacity of the bolt. With hydraulic tensioning, only pure tensile force is applied. The bolt remains free of torsional stresses.

Elimination of friction losses

With torque-based tightening, up to 90 percent of the energy applied is lost due to friction in the thread and under the bolt head. Since the coefficient of friction is never exactly constant, the actual preload force varies considerably. With the bolt tensioning cylinder, this friction is completely eliminated during force application. The result is unparalleled accuracy of the desired preload force.

Protection of components

Since the nut is turned without load during tensioning, there is no wear or seizing on the thread flanks or the contact surfaces of the flanges. This protects high-quality components and facilitates later disassembly for maintenance purposes.

Uniform tightening in multiple applications

By connecting several bolt tensioning cylinders simultaneously to a common hydraulic pump, flange connections can be tightened absolutely uniformly. This prevents one-sided tilting or uneven gasket loads, which is particularly critical in pipeline and apparatus construction.

At hyTool, quality comes first. Our tools and systems are reliable, durable, and meet all relevant national and international standards. Each product is tested, documented, and designed for continuous professional use – so you can rely on safe and reproducible results in every application.