Principles that should be paid attention to when using hoses

November 23 14:30 2021

Due to the particularity of the mechanical structure and the location of its hydraulic actuators, a large number of hoses are used in the pipeline design of the hydraulic system. Unlike metal pipes, hoses are flexible, so they are mainly used to allow relative movement between the parts connected at both ends of the hose, and can simplify pipe routing and installation. It is much simpler to arrange a hose to bypass or traverse a series of obstacles than to bend or install a rigid pipe. Building a hard pipe system is often more costly and time consuming than building a hose system.


Principles that should be paid attention to when using hoses

1) Determine the appropriate bending radius

Although many hose manufacturers are currently able to provide hoses that can be bent to a radius smaller than the radius specified in the published industry standards, it should be avoided that the bending curvature of the hose is less than the recommended minimum radius of curvature to avoid shortening the service life. Therefore, the pipe layout must first provide a sufficient bending radius. The bending radius of the hose after installation should not be less than 8~10 times the outer diameter of the hose. The roots of the joints at both ends of the hose are not allowed to be bent. A certain straight section should be reserved, and its length should not be less than 6 times the outer diameter of the hose. Times: In order to avoid sharp bending, methods such as winding springs or supporting steel belts on the outside of the hose can be adopted to make the bending gentle.

2) Correctly determine the hose length

Because the hose is flexible, its flexibility must be considered when determining the length of the hose. Depending on the type of hose, the hose can be extended by 2% and shortened by 4% when the pressure changes. This change in length can fatigue the steel wire layer of the hose and cause damage, especially at the interface of the hose connection. Therefore, taking into account the shrinkage of the hose, it is necessary to stay a little longer when cutting as compensation. If the length of the hose is not enough, it can be lengthened by connecting two hoses through a transition joint.

3) Avoid the hose being twisted

For hoses that are bent in the same plane, when there is relative movement between the two connected parts, avoid twisting the hose, otherwise the pressure-bearing capacity of the hose will be reduced. The test results show that twisting the high-pressure hose by 5° can reduce the service life by 70%, and twisting the hose by 70 can reduce the service life by 90%. In order to avoid twisting, you can draw a line parallel to the center line on the hose with chalk before assembling, so as to check whether the hose is twisted after installation.

4) The treatment method that the hose needs to be bent in multiple planes

The layout of the hose is usually carried out in the later stage of the design work, so it is difficult to find the ideal path. Multi-planar bending can often be avoided by reorienting the hose. If this does not work, then a hose clamp should be installed between the two bends and provide sufficient length on both sides of the hose clamp to release the tension of the hose wire layer. This length depends on the quality of the hose, the degree of bending and the steel wire layer of the hose, so it must be designed separately for different objects.

Another alternative is to use a separate piece of hose for each bend in the plane, and install a hose joint and hose clamp between the two bends. But because this method is not only costly and long installation time, but also increases the potential for leakage at the hose connection. Therefore, less adoption.

5) Provide protection

Now hose manufacturers offer a variety of products with wear-resistant shells. Through analysis, it was found that approximately 80% of hose failures were due to external physical damage, and wear proved to be the main cause. The wear is mainly caused by the hose repeatedly rubbing against the surface of the equipment or between the hoses. In order to avoid wear, hose clamps should be used to fix the hose and prevent it from rubbing against adjacent surfaces. The tightness of the pipe clamp should be appropriate to prevent the hose from moving, but if it is too tight, it will compress and damage the hose. The hoses on both sides of the pipe clamp should have a suitable margin to compensate for the expansion and contraction of the hose. Further protection can be provided by sleeves. A spring-like metal sleeve protects the hose from being squeezed. Soft sleeves can prevent the hose from being worn out. Some types of sleeves must be installed by sliding along the hose from the unconnected end of the hose. There is no need to disconnect both ends of the hose when installing a casing with an opening along the length. Both types of casings can tie multiple hoses together. Try to avoid contact and friction between the hose and the machine or the cab to prevent the outer rubber layer and the steel wire braid from abrading. In sections that may have mechanical friction with the outside world, they should be protected by wrapping canvas belts or rubber tubes.

6) Adapt to exercise

In addition to torsion and wear, if the hose can not properly adapt to the movement of the working device. Then it will be damaged very quickly. For example, when connected to a swingable hydraulic cylinder. The length and arrangement of the hose must be appropriate to avoid kinking or bending beyond the recommended minimum radius. When multiple lengths of hoses are arranged close to each other. And a part of it will have linear movement. At this time, a hose conveyor should be used to keep the hoses neat and avoid tangling, twisting and rubbing against each other. Some special types of hose conveyors can also isolate possible external conditions such as falling objects, friction, chemicals, or high temperatures.

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