17 Common Problems and Solutions for Hydraulic Bolt Tensioners
(Last Updated On: April 6, 2022)
If the bolt tensioner is used for a long time, there will be some small problems, which will affect the work efficiency. What are the common problems with bolt tensioners? TorcStark summarizes some common problems of bolt tensioners to help you make better use of it.
How to deal with the problem of oil leakage from the bolt tensioner?
The bolt tensioner is likely to have oil leakage problems during use. Possible reasons: The upper and lower sealing rings are worn, or have aged, the bolts are not tightened or damaged, or the bolt tensioner is over-traveled. After determining the cause of oil leakage, please take relevant measures immediately: replace the sealing ring, tighten or replace the screw. Please note that when using the hydraulic bolt tensioner, you must be well protected and pay close attention to the situation of the screw tensioner. If there is an oil leakage problem, you must stop the oil pump in time and release the oil pressure.
How to deal with the problem that the bolt tensioner is stuck on the bolt and cannot be removed?
During the use of the hydraulic bolt tensioner, there may be a problem that it cannot be removed. This may be because when removing the nut, the hydraulic bolt tensioner is not loosened after it is installed, or the force to loosen it is not enough. It may also be that the force during the unscrewing process of the nut is too great, and it hits the bottom plane of the sliding piston. Determine the cause and take relevant measures: To remove the nut, loosen it according to the maximum lifting height of the tensioner. Of course, the operator should also follow the instructions. The upper plane of the screw cap cannot touch the bottom of the sliding piston. If it does, be sure to re-tighten the screw cap, and then remove it correctly.
What should be paid attention to when the hydraulic bolt tensioner is working?
1. Before use: Be sure to calculate the oil pressure, so as to avoid exceeding the bearing range of the bolt due to excessive working pressure, otherwise it will easily cause plastic deformation of the bolt, resulting in the bolt being damaged. Therefore, we need to obtain the applied stress according to the strength grade of the bolt, which can realize the reverse calculation of the output pressure of the pump and ensure that the deformation of the bolt is within the elastic deformation range;
2. Bolt tightening: When using a hydraulic bolt tensioner, after the bolt is tightened, it should be loosened by about 3/4 of a turn, so as to avoid pulling the bolt into the piston when the bolt is elastically reset. When pre-tightening the bolts, this will not happen;
3. Step-by-step pre-tightening bolts: When pre-tightening multiple bolts in steps, in order to reduce the interaction between the pre-tightening bolts in each step, the pre-tightening degree of the bolts should be reasonable and have tensile force. It is usually arranged according to the principle of symmetry because bolts that are pre-tightened first have an effect on bolts that are pre-tightened later on the flange plate, which may cause the equipment to malfunction. So we should pay attention to this point.
What should be paid attention to in the loading and stretching of hydraulic bolt tensioners?
1. When pressurizing, the pressure should be gradually increased. Each time a certain pressure is increased, the pressure should be stabilized and then increased, so as to avoid impact tensile force and affect the tensile effect of the bolt;
2. During the stretching process, pay attention to the stroke of the hydraulic cylinder to avoid damage to the hydraulic cylinder due to excessive stretching;
3. When performing step-by-step stretching, the order of pre-tightened bolts should be arranged symmetrically and reasonably, and the influence of the later stretched bolt on the first stretched bolt should be reduced;
4. When measuring the bolt before and after loading and stretching, put the measuring rod into the center hole of the bolt a few hours in advance before the measurement, otherwise the thermal expansion and contraction of the measuring rod will affect the accuracy of the measurement results. When measuring twice before and after the bolt is stretched, place the dial indicator in the same position of the bolt.
Under what conditions can a bolt tensioner be used?
Prerequisites for preloading and loosening with hydraulic bolt tensioners
1. The exposed length of the bolt should reach the service length of the hydraulic bolt tensioner, and the service length of the hydraulic bolt tensioner is generally not less than the nominal diameter of the bolt.
2. Between the bolts, or between the bolts and the device body, the height of the upper space of the bolts should be sufficient to install and use a hydraulic bolt tensioner.
3. The support contact surface of the equipment where the bolts are located should be flat, so as to prevent the axial instability of the hydraulic bolt tensioner and the influence of the tensile force.
4. The height of the nut is lower than the height of the tensioner support seat, and it is necessary to reserve more clearance, which cannot be less than the clearance of the stretching force.
How to correctly choose the seals of the bolt tensioner?
Causes of Seal Damage in Bolt Tensioners
The damage to the seal of the bolt tensioner is generally mainly due to contamination of the hydraulic oil, overloading of the tensile force, unqualified size of the groove or unqualified mounting surface, unqualified quality of the seal, or exceeding the allowable seal of the seal. Pressure, temperature range and many other reasons.
The main forms of damage to the seal of the bolt tensioner are wear, extrusion rupture and compression set.
Therefore, the quality of the seal of the bolt tensioner directly determines the quality of the hydraulic tensioner.
The bolt tensioners currently developed and produced are working pressures up to 150MPa. Due to the limitation of space, under the condition of constant tensile force, the volume is made small, and the working pressure even needs to reach 180MPa or 200MPa, and the seal of the stretcher will not be extruded or trimmed.
Selection of Bolt Tensioner Seals
In the selection of the seals of the stretcher, imported polyurethane materials should be used. The seal size of the bolt tensioner can be unlimited. Moreover, the ultra-high pressure seal adopts a self-excited seal. According to the strength of the cylinder body and the allowable range of deformation, the greater the pressure, the better the sealing effect of the bolt tensioner, and the better oil resistance, aging resistance and extrusion resistance.
How to choose the correct model of hydraulic bolt tensioner?
When selecting a hydraulic bolt tensioner, the special requirements of the working environment on the tensioner should be considered. The specific model of the tensioner should be selected according to the bolt specification and tension, and the tensioner is not suitable for all working conditions. Whether it can be used depends on the data of the bolt conditions on site. Usually the hydraulic bolt tensioner manufacturer will have a bolt condition survey form, fill in the detailed data according to the content in the form, and then the manufacturer will determine whether it can be processed according to the data provided by the user.
If you don’t know how to choose the model of hydraulic bolt tensioner, our TorcStark can provide you with door-to-door model selection service. It is suggested that the configuration method of the tensioner should cover more than 50% of the efficiency, and the number and length of oil pipes will be better. To be determined according to the site conditions.
How does a hydraulic bolt tensioner work?
The hydraulic bolt tensioner uses the hydraulic source provided by the ultra-high pressure oil pump to directly exert an external force on the bolt end, and uses the tension generated by the ultra-high pressure oil pump to stretch the bolt acting on the tensioner to the required length to slightly deform the diameter of the bolt. This makes the nut easy to loosen. Since it is not affected by the lubrication effect of the bolt and the amount of thread friction, the stretching method can obtain a more accurate bolt load. The hydraulic bolt tensioner has the characteristics of safety, efficiency and speed, and is the preferred hydraulic tool for tightening and removing bolts of various specifications.
What are the advantages of bolt tensioners?
1. No friction damage to the contact surface: it uses pure tension to directly elongate the bolt, no torsional shear force and lateral force, and will not cause friction damage to the connected contact surface. Ideal for precise control of bolt preload. Hydraulic bolt tensioners can be used individually or in groups.
2. It can effectively improve the efficiency: when multiple hydraulic bolt tensioners are used in parallel, it can not only improve the efficiency, but also make the force more uniform. It is especially important for high pressure sealing flange connections. If the bolt center distance is small and the radial dimension is limited, a two-stage structure can be adopted, and the axial dimension is sacrificed to ensure the radial dimension. When the outer diameter remains unchanged, the effective area of the piston doubles, and the force also doubles;
3. Increase the output pressure of the pump: The hydraulic bolt tensioner can greatly increase the output pressure of the pump and increase the tension of the tensioner to meet the requirements of high-strength and high-torque bolts.
How to Maintain a Bolt Tensioner?
When using the hydraulic bolt tensioner, it should be carried out in strict accordance with the standards, and the working pressure and elongation length of the hydraulic bolt tensioner should not be increased at will. After the work is completed, the equipment should be wiped clean and properly kept, especially the oil inlet surface should not penetrate into the ash bottom to prevent damage to the cylinder and piston after the ash enters the cylinder. When replacing the O-ring and the support ring, attention should be paid to the joint to ensure the sealing effect.
What are the common types of bolt tensioners?
1. Ordinary models: The ordinary models are used more by users. This type of stretcher is lighter in weight, higher in precision, wider in use and smaller in size than others, which can save a lot of space;
2. Single-stage, double-stage reset type: In the process of using the stretcher, a single-stage or bipolar piston may be used. Different piston types have different effects. For single-stage reset pistons, the performance is stable even under heavy use. However, if the space usage requirements are limited, the bipolar reset type can be considered;
3. Interchangeable tensioner head: In actual use, users have higher requirements for practicality. For this tensioner that can adapt to bolts of multiple specifications, the actual frequency of use is also higher.
Why use a tensioner to remove and install bolts?
1. A clearance fit is used between the hydraulic super-tight fitting bolt and the reaming hole, and the clearance is generally controlled between 0.05% and 10.15% of the diameter of the reaming hole. The installation can be carried out manually, which can effectively avoid the situation that the joint surfaces are engaged with each other;
2. Tighten the taper sleeve through the tensioner, and the super-tight bolt can better correct the matching hole without alignment, which greatly improves the alignment and positioning technology of the shaft system;
3. During the installation process of the expansion taper sleeve of the tensioner, the axial displacement is limited, and the expansion taper sleeve only expands radially in the hinge hole without axial friction, so the surface of the hinge hole can be protected from scratches and burrs ;
4. When the hydraulic stretching technology is used, the stretching amount is calculated, so that the stretching amount on each bolt is almost the same, and there will be no loosening and tightening;
5. When dismantling, the pressure oil can be injected into the dismantling pipeline to generate a loosening force between the cones, forcing the expansion cone sleeve and the cone rod to push apart each other to achieve the effect of disassembly;
5. The super-tight bolts reduce the uncertainty in the bolt disassembly and installation process, shorten the downtime, and greatly reduce the inspection time and cost.
How to choose a cost-effective hydraulic bolt tensioner?
1. Security. The hydraulic bolt tensioner should have pressure relief protection during the stroke, and there are obvious safety signs to remind that when the maximum pressure is exceeded, the pressure should be automatically released to prevent safety accidents.
2. Sealing. The hydraulic bolt tensioner adopts a unique integrated design of piston and hydraulic cylinder, with low friction, no thread displacement seal and support ring.
3. Accuracy. The hydraulic bolt tensioner has a unique moving piston design that can be tilted in any direction within 3 degrees without causing accuracy problems.
4. Interchangeability. The parts of the hydraulic bolt tensioner are interchangeable. Support bridges, stretching heads and pull tabs are interchangeable. Applicable to all sizes of bolts.
6. Price. Based on the above four points, according to the actual working conditions, the price of different types of hydraulic bolt tensioners will also change.
What is the difference between a hydraulic bolt tensioner and a hydraulic wrench?
1. Scope of application: The hydraulic bolt tensioner is a high-efficiency tool developed on the basis of the function of the hydraulic wrench, and it has a strong tensile strength. When it is necessary to disassemble and assemble large nuts inside the equipment or operate multiple nuts at the same time, the tensioner is more efficient than the hydraulic wrench, and at the same time, it can ensure the work progress. If it is in some specific spaces, the tensioner is not as easy to use as the hydraulic wrench, but in most cases, the tensioner is widely used.
2. Restriction in small spaces: Due to the high work efficiency of the tensioner, there is no problem in using it during equipment maintenance, but if it is some old equipment, hydraulic wrenches are more suitable, especially for some small spaces. When operating in a different place, using the tensioner is not as easy as a hydraulic wrench, which is also one of the differences between the two.
How to choose the preload of the bolt tensioner?
In order to avoid the occasions where the compression force is too small due to vibration loosening or fatigue, the preload force is selected mainly according to the preload force control method used in the assembly and whether the bolts allow the tensile force to exceed the yield point. In the case of a sealed bolted connection without gaskets, the connection is subjected to tensile loads to meet the requirements of safety regulations. Everyone should pay attention here: the upper limit of the pre-tightening force of the pressure vessel bolt connection is 0.5-0.6.
How to solve the problem that the hydraulic bolt tensioner cannot maintain pressure?
Reasons why the hydraulic bolt tensioner cannot maintain pressure: oil leakage at the connection, oil leakage from the sealing ring of the hydraulic bolt tensioner, the oil drain valve is not tightened, and the pump or valve is faulty.
Solution: reconnect after cleaning the joint threads, and tighten the joints; clean the cylinder body and replace the hydraulic oil used in the seals, and keep it clean; completely tighten the oil drain valve; repair or replace a new pump or valve.
In addition, when you pressurize the hydraulic bolt tensioner, try to pressurize it as evenly as possible. Each time a certain pressure is increased, the pressure must be stabilized before continuing to increase the pressure, so as to avoid excessive impact tension, which will affect the pre-tightening of the bolt.
How to Extend the Life of Bolt Tensioners?
1. Check the oil pump before use: The reason for checking the oil pump before use is to avoid the plastic change of the bolt due to the low oil pump during the working process, resulting in damage to the bolt. Therefore, check the counter value of the oil pump before working;
2. The pressure should be balanced during use: the stability of the hydraulic bolt tensioner is still relatively high. The reason for its high stability is that its impact force has little change in the preloading effect. In order to ensure that the impact force will not have a large change in the bolt preload, the preload force applied during pressurization should be balanced;
3. Do not exceed the maximum design stroke: In order to ensure the use effect of the hydraulic bolt tensioner, it should not exceed its maximum stroke warning line during use. Once exceeded, it will cause great damage to the stretcher itself;
4. The effect of step-by-step pre-tightening can be adopted: in the process of using the bolt, for its own calibration force and working stability, the method of step-by-step pre-tightening can be adopted.
These are some of the basic problems of bolt tensioner description and solutions, if you have other questions, please comment or contact us.