Key points of hydraulic hose selection design

The hydraulic hose is an important connection part of the hydraulic component, which is used to transmit the hydraulic fluid with a certain pressure and flow to ensure the circulation work and energy transfer of the hydraulic system. Correct selection design and reasonable pipeline layout help to extend the service life of the hydraulic hose and improve the reliability and safety of the whole hydraulic system.

1 Hydraulic system for the basic requirements of hydraulic hose

The increasingly harsh use environment of construction machinery puts forward higher requirements for hydraulic hoses. Hydraulic system through the transmission of a certain pressure and fluid flow to transfer energy, in order to achieve the maximum efficiency of the hydraulic system, it is necessary to minimize the pressure loss when the fluid flows in different pipelines, in the hose selection design to minimize pressure loss and excessive heating caused by the system damage. At the same time, the influence of external high (low) temperature environment, internal hydraulic oil temperature and system instantaneous high pressure on the service life of hydraulic hose is considered.

2 Key points of hydraulic hose selection design

2.1 Hose raw materials

The hydraulic hose is usually composed of an inner rubber layer, a steel wire reinforced layer and an outer rubber layer. The inner rubber layer has the function of conveying medium to withstand pressure and protecting steel wire from erosion, which is usually synthetic rubber with fluid resistance; The steel wire reinforcement layer plays the role of the central skeleton, which provides support and pressure resistance for the hose assembly. There are two types of steel wire braided and steel wire wound. The outer rubber layer protects the steel wire reinforcement layer from damage and must have wear resistance and weather resistance.

2.2 Inner diameter of hose

When the liquid flows in the pipeline system, heat will be generated due to friction, and energy is lost in the form of heat, resulting in pressure loss. Too small inner diameter will lead to too fast flow rate, causing high friction loss and turbulence in the pipeline system, resulting in large pressure drop and heat, high heat will accelerate the wear of moving parts and aging of hoses; The large inner diameter suction pipe causes cavitation in the pressure pump port, which affects the performance of the pump and shortens the service life, and produces noise.

2.3 Hose working pressure

After determining the system pressure of the hydraulic system, the hose with the recommended maximum working pressure higher than the system pressure must be selected, and the safety factor of 1.33 must be reached. The hydraulic system is generally in a dynamic pressure state, and if the instantaneous impact pressure of the system is higher than the maximum working pressure of the hose, it not only reduces the service life of the hose, but also risks personal injury and property loss. The graph in Figure 1 shows the relationship between the actual working pressure and the service life of the hose.

2.4 Hose operating temperature

When the hose is designed and selected, the temperature of the fluid transported in the tube and the temperature of the external working environment should be considered. Whether the temperature is stable or instantaneous, it must not exceed the temperature limit of the hose, otherwise it will reduce the hose performance. When the temperature exceeds the rated use temperature of the hose, it will lead to changes in the molecular structure of the material of the hose, and these changes are irreversible. The temperature is too high or too low, which will lead to cracks and bubbles in the rubber hose, cracking and aging, and quickly reduce the service life of the hydraulic hose. The test shows that the aging speed of the hose is doubled when the operating temperature of the system is increased by 10℃. Therefore, under the comprehensive condition of high temperature and high pressure, the hose with high temperature resistance of the outer rubber layer should be selected, and the rubber hose with low temperature resistance should be selected in the cold end climate, deep cold and other low temperature conditions to meet the use of the hydraulic system. Figure 2 shows the relationship between hose operating temperature and allowable pressure.

2.5 Media Compatibility

In the selection of pipe type, it should first be clear that the working medium is oil or water-based hydraulic oil, gas or oil and gas mixture. It is necessary to ensure that the inner rubber layer of the hose, the steel wire reinforcement layer, the outer rubber layer and the hose joint equipped can be compatible with the medium used, to avoid the pressure bearing capacity of the hydraulic hose and the pollution of the working medium, and damage other hydraulic components, thereby reducing the service life of the entire hydraulic system. Especially in the selection of gas applications, it is necessary to carefully choose the pipe type, when used for more than 1.7MPa air, the hose needs to be needled to prevent the occurrence of personal injury.

2.6 Application Scenarios

When choosing a hose, it is very important to understand the purpose of the hose application, ask your customer where and how to use the hose. When using hoses and joints, it is necessary to ensure that the environment in which they are located does not have an adverse effect on the hose and joints while ensuring the compatibility. Environmental factors to consider include, but are not limited to, UV, temperature, ozone, moisture, water, seawater, chemicals and air pollutants, all of which can reduce the quality and service life of hoses and fittings.

3 Pipe Layout rules

In the process of using construction machinery equipment, there are often pipeline oil seepage, pipe explosion, bulging oil leakage, outer rubber cracking and aging, etc. These problems are often caused by unreasonable pipeline layout. Reasonable pipeline layout is helpful to prolong the service life of hydraulic hose and improve the reliability and safety of hydraulic system. Improper installation may result in personal injury and property damage. Therefore, when installing and arranging hoses, the following factors should be fully considered:

1), because in the high pressure state, the hose length will appear +2%~-4% change, so it is necessary to maintain sufficient relaxation. Too long hose will not only cause system pressure drop, heat loss, but also affect the appearance, resulting in unnecessary waste of raw materials. Inadequate assembly length and tube expansion will affect power transmission and reduce tube life. Figure 3-6 below shows the proper assembly installation for maximum efficiency and economic benefit.

2) When the system pressure rises, the hose length will change. Therefore, clamp should not be used to fix the bent part of the hose. In addition, do not clamp the high pressure and low pressure lines together.

3), the high temperature environment will rapidly reduce the service life of the hose. Therefore, the pipe layout should be as far away from the heat source as possible, if necessary, add a high temperature protective sleeve or heat insulation device outside the hose to avoid heat damage to the hose.

4), the hose installation should avoid contact with other parts, so as not to wear the outer rubber layer. If the hose is inevitably crossed with other parts or may have friction with other mechanical surfaces when the machine is working, wear resistant nylon or steel wire sheath should be used to protect the rubber layer of the hose from damage.

5), in the pipeline layout, should give priority to the layout of the larger diameter of the pipeline. Because the large pipe diameter hose is not easy to bend and move, especially in the space is relatively narrow, it is easy to replace and increase the subsequent hose.

6), avoid the hose twisted installation. When the connected components at both ends of the hose assembly are in relative motion, the hose should not be twisted, such as being installed in a distorted position, the hose service life is reduced, and the pressure in the twisted tube body will also make the joint connection loose, so in the design, the hose should be as far as possible to keep the relative movement of the components in the same plane bending, which can be achieved by changing the Angle of the joint. In special cases, when both ends of the hose assembly need to be bent in two different planes, a longer hose can be used and a pipe clamp can be installed at the conversion plane to fix it so that each part moves on the same plane.

7), under no circumstances can make the bending radius of the hose less than its allowable minimum bending radius, too small bending radius will cause the inside of the hose easy to wrinkle, and the greater the bending outside stress, and the greater the flow loss caused by bending. Use appropriate protective sleeves at small bending radii to ensure that the hose does not bend excessively. At the same time, in order to avoid hose distortion, the bending direction of the pipe body should be consistent with the direction of mechanical movement.

8), hydraulic hose pipe layout should be fully considered neat and beautiful, convenient hydraulic components damage, inspection and maintenance, parallel pipeline layout, reduce cross.

4 Closing remarks

Hydraulic hose assembly as an important component of hydraulic system, its quality reliability directly affects the performance of the whole equipment. In this paper, the key factors affecting the performance of hose assembly are analyzed from the stage of hydraulic hose design and selection, and the important matters that should be paid attention to in the later stage of pipeline layout are studied and discussed. It is concluded that the correct selection of hydraulic hose and reasonable pipeline layout are conducive to improving the service life of the whole hydraulic system and reducing the occurrence of hydraulic component failure.