Types of pullers, tensioners and principle of their operation.
A hydraulic winch is a device used to pull steel or synthetic ropes. In all types of winches, the rope is pulled using hydraulic motors. Hydraulic motors are cylinders that replace hydraulic pressure and fluid flow for torque and rotation. In terms of construction, hydraulic motors are identical to hydraulic pumps, but they perform the opposite functions. Due to the pulling system, we distinguish capstan and drum winches with different power supply systems, such as combustion or electric.
Capstan winches pull the rope through the capstans, i.e. 2 rollers connected mechanically or hydraulically on each groove on which the rope is wound, and then it is rolled onto the drum with a uniform force. This relatively inconspicuous element has great power and allows you to maintain a constant force and speed of pulling the rope. The rope pulled by winches is wound 6-8 times around the winches, and then goes to the spool where it is ultimately wound up. Such a system is possible because the surface of the rope and winches has adequate friction that does not allow the rope to slip. This is the most popular and reliable way to pull ropes in industrial applications, because hydraulic systems are virtually trouble-free. The condition is, of course, being made of suitable materials and components.
Capstan winches are used in virtually every branch of the economy where rope pulling is necessary. Due to the way they can be used, they can be further divided into winches with limited and unlimited rope length. The former have a spool with a rope mounted under the casing for easier movement between construction sites and they are used in situations where the length of the rope can be limited to 1-1.5 km, e.g. when laying power cables, telephones, gas or water pipelines sewerage and many others with different pulling power up to 100 tons. For example Model UP50
In situations where a much longer rope length is necessary, winches with an external drum are used. This solution allows connecting ropes to an infinite length. This solution is used, among other applications, for retracting overhead cables on high-voltage lines, where the retractable sections often reach up to 6-8 km, e.g. model F280.40
Drum winches are used as lower power winches and usually as an auxiliary. The rope is wound directly on a drum installed directly on the winch on which the rope is wound. All the force with which the rope is pulled is on the wound rope, which causes the rope to tighten on the drum, which is not advisable for the life of the rope, and is also not comfortable during operation. According to physics, with each winding of the winding rope, the strength of the towed rope also changes because the inside diameter of the pulling drum changes. An example of this can be model F206.10
Each of these winches can be powered by a petrol or diesel or electric engine. Diesel winches are most commonly used due to their greater torque and economy, but electric and battery winches are increasingly being introduced. The battery winch system is desirable in many places with tougher environmental standards, as well as tunnels and enclosed spaces. Modern electric winches have power similar to combustion ones, and the only drawback is the battery capacity, which limits the length of work. Electric winches are fitted with IBS (Intelligent Battery System) systems, i.e. a battery management system, which ensures that when pulling out, we will not use all energy and the batteries will not be overloaded.
To ensure the longest possible operation time, while maintaining full functionality, each hydraulic winch requires periodic maintenance. It is no different in the case of hydraulic pullers, which, working in difficult conditions, are exposed to the operation of individual elements, which translates not only into the difficult functioning of the device, but also to reducing the safety of working with the winch. That is why it is necessary to perform periodic inspections of equipment and maintain it by cleaning and lubricating moving parts and replacing worn parts of the winch. An important factor is also the regular change of oils in the engine and hydraulic system, which will improve the service life of the device. Apart from the above activities, remember to regularly clean the machine of dirt accumulated during operation, and you will be able to enjoy trouble-free operation of the hydraulic puller for many years.
How to choose the power of pullers and hydraulic tensioners
Cable – underground winches
To choose the right power of the cable pullers it is necessary to know what kind and diameter of cables will be pulled in. The weight of the cable is irrelevant because the cable is not lifted, only pulled in an open trench on cable rollers or a conduit pipe. In both cases, the friction should be minimized so that the cable is pulled as gently as possible. Currently manufactured cables are very delicate due to their design. They are made of brittle metal alloys, plastic fillings and thin return wires, which after excessive stalling are quickly damaged. Therefore, the maximum cable pulling force is determined by the manufacturers and this is the only determinant of the maximum cable pulling force and selection of the cable winch strength.
To pull long lengths of cable, the only way is to properly lay straight cable rollers in the excavation and to properly corner cable rollers at corners. Any wrong profiling will result in increased friction resistance, which is synonymous with increased pulling force. If we pull a cable in pipes, the only method is to thoroughly clean the pipeline and use slip fluids, which minimizes friction by up to 80%.
In the case of longer sections with many bends, where it is not possible to position the rollers in a way that reduces friction to the level of safe pulling of the cable, supportive devices are set up along the line called cable dogs. It is a device operating on the principle of pushing the cable in this way reducing stress.
Overhead line sets – Puller – Tensioner – operating method
The quickest method for calculating the minimum force required to pull in overhead cables is presented below.
First, we calculate the braking force of the cables based on the cross-section of the wires. The weight of the cable is not taken into account.
– FT – tensioner force (daN) = (Cable cross section in mm2) X 4 X Number of wires per phase.
For example – AFL 6-240 cable; Diameter = 21.7 mm; Cross section = 240 mm2
For lines with one cable per phase
Calculation of the minimum power – Tensioner = (240 x 4) X 1 = 960 daN, i.e. about 1 Ton
For a line with three cables per phase
Calculation of the minimum power – Tensioner = (240 x 4) X 3 = 2880 daN, i.e. about 3 Tonnes
To calculate the minimum puller force, add a minimum 30% of the tensioner force according to the formula below:
– FP – puller force (daN) = FT + 30%.
For lines with one cable per phase
– puller = 960 daN + 30% = 1248 daN
For a line with three cables per phase
– puller = 2880 daN + 30% = 3744 daN
It is possible to determine the pull-in force of the cables without going into the exact calculation, taking into account the specific load of the cables 4 kg / mm2.
This is, of course, the minimum strength of the devices necessary to overcome the resistance when pulling cables on medium and high voltage overhead lines.
However, to make the most of the equipment at the right speed, we suggest buying machines with a strength 2 times higher. This will allow you to pull cables up to 5km per hour.