What Is A Bolt Tensioner?

Bolt tensioner is a bolt pre-tightening and disassembly tool. It is like a ring jack installed on bolts and nuts. With the help of hydraulic power provided by tensioner pumps, the bolts are stretched in the elastic deformation zone according to the allowable elasticity of the material to achieve the purpose of tightening or removing the bolts. The biggest advantage of the tensioning of bolts is that multiple bolts can be fastened and disassembled at the same time. The distribution force is even. It is a safe, efficient and fast tool, and it is the best way to fasten and disassemble bolts of various specifications.

Generally speaking, tensioning machine are also called bolt tensioners, hydraulic tensioners, and bolt stretcher and so on.

How Does A Hydraulic Bolt Tightening Machine Work?

Working Principle

The thread friction between the nut and the washer consumes more than 80% of the torque energy on the nut or bolt, leaving less than 20% of the energy to produce effective tension on the bolt shank.

This change in friction loss, from one bolt to another, causes uneven tension on the bolts, so a bolt tensioning tools has appeared to solve this problem.

The hydraulic tensioning tool is generally composed of a hydraulic tensioner pump, a high-pressure hose, a pressure gauge and a stretching body. The hydraulic tensioning pump is the power source, the pressure gauge reflects the output pressure of the pump, and the high-pressure hose is connected to the hydraulic tensioner pump and the stretching body.

Stretching body is an executive element that realizes bolt stretching. It is mainly composed of a piston cylinder, a piston, a supporting bridge and a tension nut.

When working, the high-pressure oil output by the power source is delivered to the piston cylinder through the high-pressure hose, and the piston in the piston cylinder moves upward under pressure, driving the tension nut to move upward.

The tension nut is threadedly connected with the working bolt. With the extension tension generated by the hydraulic source provided by the ultra-high pressure oil pump, and the extension force determined by the material’s tensile strength, yield coefficient and elongation rate, the bolt tensioning equipment exerts force on the bolt to elongate it in the elastic deformation zone.

At this time, the bolt diameter is slightly deformed, the working bolt is elongated, the bolt elongation reaches the required deformation, and the deformation is controlled within the elastic deformation range, and the pre-tightening or disassembly operation can be carried out. Finally, return the working bolt to its original shape by hydraulic or mechanical return.

Work Process

The hydraulic nut tightener is like a ring jack mounted on bolts and nuts. The jack pushes the bolt connection and pulls the end of the bolt. The diameter of the bolt must be at least one longer to accommodate the bolt tensioning tool.

Since the force generated by the jack directly acts on the end of the bolt, a tension equal to the load generated by the jack is generated in the bolt shank.

In the case of tension applied by the jack, the nut can be rotated with zero torque until it is tightened.

Then the load applied by the jack is relaxed, and is retained in the bolt shank according to the high percentage of bolt length and diameter, so as to realize the pre-tightening or disassembly of the bolt.

The Characteristics And Differences Of Tensioning Equipment

Generally speaking, there are four main types of multi jackbolt tensioners: common general type, interchangeable tensioner head type, single-stage reset type and dual-stage reset type. The working pressure of these four stud tensioning is 150Mpa.

1. The ordinary type is suitable for the stretching of single specification bolts. It is light in weight, high in precision, small in size and compact in structure;

2. Interchangeable tensioner heads have strong versatility, which can be applied to bolts of multiple specifications by replacing the tensioner heads;

3. Single-stage reset type piston automatic reset design, suitable for frequent use;

4. The design of double-pole reset type double oil cylinder is suitable for working conditions with narrow space.

In TorcStark®, there are four main types of hydraulic nut tensioner sold.

1 HLD series single-stage hydraulic bolt stretcher. It is characterized by small size, light weight and easy replacement of tie rods and is mainly used in the wind power industry.

2 DLD series simple bolt tensioning machine. It is a mechanical reset design with over-stroke warning indicator line.

3 TSD Series single-stage hydraulic bolting tools. It is designed with automatic return stroke, which adapts to bolts of different specifications.

4 MSD Series multi-stage hydraulic bolt tensioning tools. Its characteristic is to be used for 10.9 grade high-strength bolts, such as the wind power industry. Three-level security protection, automatic return.

The hydraulic bolt tensioning equipment provided by TorcStark® can almost adapt to the engineering needs of the entire industry, so buying a bolt tensioner from TorcStark® will be a good choice!

How To Use Nut Tensioner Correctly For Beginners


1 Evaluate the bolt diameter, nut size, bolt grade, washer thickness, washer diameter, free bolt protrusion length and bolt load, and then check the technical specifications of the multi stud tensioner to ensure that it provides the appropriate hydraulic pressure to achieve the required preload rate.

2 Screw the round nut into the bolt, and insert the toggle handle into the toggle hole until it is firm.

3 Insert the support seat of the hydraulic tightening tools to cover the round nut.

4 Screw the hydraulic tensioner into the bolt, and use the toggle handle to tighten the tensioning head until there is basically no gap between the parts.

5 After installation, insert the quick connector of the high-pressure oil pipe connected to the ultra-high pressure oil pump into the quick connector on the hydraulic bolt tightening machine.

Start Up

1) Operate the ultra-high pressure oil pump, input high-pressure oil to the hydraulic tightening device cylinder, the piston starts to work, and the hydraulic tensioning device enters the working state. At this time, pay attention to the working pressure of the ultra-high pressure oil pump and the stretching length of the bolt tensioning device. Control within the set range.

2) When the working pressure and stretching length of the stud tensioning equipment reach the rated value, the ultra-high pressure oil pump should stop working immediately, insert the toggle handle into the round nut toggle hole, and turn the round nut clockwise to firm it in place.

3) During use, if the elongation needs to be increased due to the process requirements, after the round nut is tightened in place, the ultra-high pressure oil pump should be relieved according to the operating procedure, and then the toggle handle is inserted into the piston of the stud bolt tensioner. Move the hole and move the handle to reset the piston. Then operate according to the above method until the process requirements are met.


After the jackbolt tensioner is finished working, the ultra-high pressure pump is first relieved and then disassembled. There are two disassembly methods, which can be selected according to the working environment:

1) Move the extension head with the toggle handle, first drain the hydraulic oil in the oil cylinder to the ultra-high pressure oil pump, reset the piston, and then disconnect the quick connector connected with the high-pressure oil pipe, and unscrew the bolt of the hydraulic stud tensioner. Take out the support seat and end the entire stretching process.

2) Disconnect the quick connector connected with the high-pressure oil pipe, first unscrew the bolt of the hydraulic tensioner, take out the support seat, loosen the screw on the end of the piston with an Allen wrench, and then clamp the tensioner straight in the middle of the vise , Slowly move the screw rod to drain the hydraulic oil stored in the cylinder until the piston is fully reset.


Large hydraulic tensioning equipment are ultra-high pressure products and should be used correctly, otherwise the expected results will not be achieved, and danger may even occur.

1 The operation must be carried out in strict accordance with the methods and procedures required by the manual, and the input working pressure and stretching length of the long bhydraulic stud bolt tensioner must not be increased at will to avoid damage to the sealing ring and related parts.

2 The oil pressure must be calculated before use to avoid excessive working pressure that exceeds the bearing capacity of the bolt, causing plastic deformation of the bolt and destroying the bolt.

The tensile force generated by the hydraulic nut tightening tool is equal to the product of the output pressure of the power source and the effective area of the piston. Therefore, the allowable stress can be calculated according to the strength grade of the bolt used, and the output pressure of the pump can be reversed. Ensure that the deformation of the bolt is within the elastic degeneration, and complete the work without damaging the bolt.

3 During the pressurization process, pressurize as evenly as possible. Every time a certain pressure is increased, the pressure shall be stabilized and then increased to avoid excessive impact tension and affect the pre-tightening effect of the bolt.

4 In the stretching process, pay attention to the maximum design stroke of the tensioner. If the maximum stroke is exceeded, the seals may be damaged, or a safety accident may even occur. Generally, the hydraulic bolting equipment has a maximum stroke warning line, and users are required to pay attention to the maximum stroke at any time during use.

5 When using the hydraulic bolt tightening tools to remove the bolt, after the tension nut is tightened, loosen about 3/4 turn to avoid tensioning the tension nut on the piston when the bolt is elastically reset. When the bolt is pre-tightened, there is no such problem. This part of the force is mainly borne by the working nut instead of the tension nut.

6 When pre-tightening multiple bolts step by step, in order to reduce the mutual influence of the bolts pre-tightened in different steps, the order of bolt pre-tightening and the tensile force should be reasonably arranged. Generally, the order should be arranged according to the principle of symmetry.

For example, when a single hydraulic bolt tightening equipment is used to pre-tighten the flange with 8 bolts, the tension control of each step is more complicated, because the bolts that are pre-tightened later on the flange must have an effect on the bolts that are pre-tightened first.

7 After finishing the work, it should be wiped clean and kept properly, especially the oil inlet should be wiped clean to prevent dust from entering the oil inlet to damage the cylinder and piston.

8 When replacing the O-ring and supporting ring, pay attention to the coincidence to ensure the sealing effect.

Why Use A Hydraulic Bolt Tensioning Machine?

There are many benefits of using bolt tightening equipment. Compared with hydraulic torque wrenches, hydraulic bolt tensioners are better in some aspects.

Bolt connection is one of the key elements that affect the integrity and reliability of the project. If you do not use advanced tool technology, bolted connections will pose a serious hand safety threat, and due to disassembly speed and reliability issues, your engineering plan may be greatly changed.

Tightening machine for bolt technology provides the highest level of accuracy, productivity and safety for critical connections in the energy industry.

In order to provide a leak-free bolt assembly, you must apply the correct amount of compressive load to the sealing surface or gasket. Tensioning is the best way to transfer this load because it is accurate, fast and safe.

Accurate: Because the tensioning provides the reliability needed to transfer precise bolt loads to the joint. Multiple bolt tensioning tools are evenly distributed around the joint, causing the gasket to flow into the flange surface irregularly, providing a better seal.

Fast speed: Because bolt tensioning can eliminate crosstalk compared with bolt torsion, and provide bolt load and washer compression on the entire joint at the same time.

Tensioning also greatly reduces the possibility of threaded fastener wear, helping you avoid potential delays and rework.

Safety: Because the bolt tightener machine is a hands-free technology, it can minimize work-related accidents.

In short, it helps to ensure that your operations are leak-free: it saves you time and money, but the most important thing is to ensure the safety of your employees.

The Following Is A Summary Of Other Advantages Of Bolt Tightening Tools:

1. Generally, mineral oil is used as the working medium, the relative moving surface can be lubricated by itself, and the service life is long.
2. Light weight, small size, small movement inertia and fast reaction speed.
3. Various components of hydraulic transmission can be conveniently and flexibly arranged according to needs.
4. The overload protection can be realized automatically.
5. Convenient operation and control, and multiple bolts can be tightened at the same time. Save labor costs.
6. It is easy to realize linear motion.
7. It is easy to realize the automation of the machine. When the electro-hydraulic joint control is adopted, not only a higher degree of automatic control process can be realized, but also a remote control can be realized.
8. It can be used as a device for hydraulic interference connection to apply axial force for top pressure installation
9. It can eliminate torsional load;
10. High accuracy;
11. Greatly increase the quality and safety performance of bolt connections;
12. Will not damage flanges and other components;
13. There is no need to consider the influence of friction coefficient;
14. Suitable for bolts of different diameters;
15. It is easy to disassemble;
16. Strong versatility;

Application Of Tensioning Tools

It can be widely used in metallurgical mining, petrochemical industry, shipbuilding industry, power system, rolling stock, heavy machinery, railway, aerospace, and other industries.

Especially in the work environment with serious pollution or limited space area, hydraulic bolt stretcher is difficult to replace by any other tools, and it is the ideal equipment for the assembly of large and medium-sized mechanical products and equipment maintenance.

According to different working conditions, application conditions and user requirements, special hydraulic bolt tightening machine can be customized.

Where To Buy Bolt Stretchers?

Before choosing to buy a tensioning tools of bolts, you need to pay attention to some issues:

Bolt diameter.
The protruding length of the free stud.
Nut size.
Washer thickness and diameter.
Bolt grade.
Bolt load requirements.

Fortunately, bolting tools come in various shapes and sizes.

You need to understand most of the above data to choose the right hydraulic tensioning, which will be a troublesome thing for you.

Therefore, buying a bolt tensioner from TorcStark is a very good choice. You can tell our product experts about your needs or your business by email, and we will provide you with the best product portfolio or customize it for you.

You will receive our hydraulic bolt tensioner’s technical parameters and the best price, as well as the most optimized plan for your project. In this way, you will save a lot of time in the purchase process and focus on your project.

TorcStark’s hydraulic bolt tensioner uses aluminum-titanium alloy material, which is light in weight, easy to use, efficient, and accurate in pressure output.

Various types of bolt tensioning tools have complete specifications and are suitable for all walks of life.

TorcStark also has a complete bolt tensioning systems of supporting supply capabilities, and has passed the European Union CE, ISO9001 and other quality certifications.

TorcStark is top bolt tensioner manufacturer and supplier. If you are looking for a hydraulic bolt tensioner with good quality and low price, please contact us by email(torcstark@gmail.com) get bolt tensioner price list.