Significance and method of hydraulic system flushing

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【Summary】From the perspective of use, the first condition for the normal operation of the hydraulic system is that the inside of the system must be clean. Before the operation of new equipment, or after a piece of equipment has undergone major repairs, contamination of the hydraulic system is inevitable. It is possible to bring contaminants into the system during the installation of hoses, pipes and fittings. Even new oils will contain some unexpected contaminants.

　　1. The significance of hydraulic system cleaning

　　From the perspective of use, the first condition for the normal operation of the hydraulic system is that the inside of the system must be clean. Before the operation of new equipment, or after a piece of equipment has undergone major repairs, contamination of the hydraulic system is inevitable. It is possible to bring contaminants into the system during the installation of hoses, pipes and fittings. Even new oils will contain some unexpected contaminants.

　　Must take measures to filter out the pollutants as soon as possible, otherwise there may be failures soon after the equipment is put into operation, and the early failures are often very serious, and some components such as pumps and motors may be fatally damaged.

　　The purpose of 　　 system flushing is to eliminate or minimize the early failure of equipment. The goal of flushing is to improve the cleanliness of the oil and keep the cleanliness of the system oil within the pollution tolerance of key hydraulic components in the system to ensure the reliability of the hydraulic system and the service life of the components.

　　2. Circulation flushing device

　　Circulating flushing device generally adopts independent large-flow high-pressure flushing device or working pump station of the system for circulating flushing operation of pipelines.

　　The output flow of the independent high-flow high-pressure flushing device is generally more than 1000 liters/min. It should be composed of 3-4 high-pressure pumps and one low-pressure pump. According to the parameters of the metallurgical hydraulic system, the flow rate of the high-pressure pump (31.5MPa) is configured to 250 liters/ Min, 160 liters/min, 100 liters/min, 63 liters/min and low pressure pump (2.5MPa) 400-600 liters/min can constitute different flushing pressure\flow needs.

　　The output pipeline interface of the circulating flushing device should not only enable the output flow of all flushing pumps to flush one flushing circuit at the same time, but also form multiple independent flushing circuits.

　　The use of the working pump station of the system itself for the circulating flushing of pipelines has also been more and more widely used and recognized. The use of working pump stations to flush the system pipelines is a reliable method for efficiently and quickly reaching the flushing quality and has more advantages. Specifically, it saves valuable time, saves a lot of temporary piping materials, and can use the formal electrical protection of the working pump station itself and the circulation cooling and internal circulation filtering functions in the system to make the system flushing effect of the pipeline better and faster.

　　3. Steps of circulating washing

　　Circular flushing is generally divided into the flushing of the main pipeline from the hydraulic pump station to the control valve frame and the flushing of the control valve frame to the oil cylinder and oil motor branch pipeline.

　　According to the requirements of pipeline flushing precision, it is divided into coarse flushing of intermediate pipelines and fine flushing of all pipelines.

　　The flushing connection circuit of the hydraulic pump station to the main pipeline of the control frame is relatively simple, only need to be connected at the end of the main pipeline.

　　The flushing of the control valve holder to the oil cylinder and oil motor branch pipeline is relatively complicated. Sometimes it is necessary to make a lot of temporary flushing pipes to form a flushing circuit. At this time, it is necessary to pay attention to the factors that should be considered when serial and parallel flushing mentioned earlier.

　　Flushing of the hydraulic system can be carried out as follows:

　　Before installing sensitive components (such as servo valves, etc.), assemble the pipeline and the components that are not sensitive to contaminants, and seal the end of the tube tightly.

　　Replace the sensitive components with jumper wires, connect the hydraulic circuit, fill with liquid and pressurize, and rinse until the specified cleanliness is reached.

　　The selected flushing circuit should skip sensitive components and minimize the flow resistance. When flushing, avoid dirty oil passing through the cleaned pipeline. For more complicated systems, you can choose to flush the circuit from the branch to the main pipeline, then separate the branch from the main pipeline, and then flush the main pipeline. An oil filter or filter screen is installed on the oil return road. Due to the large amount of impurities in the early stage of flushing, an 80 mesh filter screen is generally used, and a filter screen of more than 150 mesh is used in the later stage of flushing.

　　In order to improve the flushing effect, the hydraulic pump in the flushing process is preferably intermittent movement, the intermittent time is generally 10 to 30 minutes, the flushing effect can be detected during this intermittent time. During the flushing process, in order to facilitate the removal of the attachments on the inner wall of the pipe, a non-metallic hammer such as a wooden stick or rubber hammer can be used to gently tap the pipe, which can be tapped continuously or intermittently.

　　The choice of flushing medium is usually the actual hydraulic oil or test oil. Avoid using alcohol, steam, etc. to prevent corrosion of hydraulic components, pipes, oil tanks, and seals.

　　The amount of flushing liquid is generally 60% to 70% of the working capacity of the tank. The flushing time should not be too long, generally 2 to 4 hours, and not more than 10 hours under special circumstances. The flushing effect is based on the standard of no pollution impurities on the loop filter. The flushed hydraulic oil needs to undergo quality inspection to determine whether it can continue to be used.

　　Attention should also be paid to the flushing process:

　　(1) The fuel tank should be closed to reduce the chance of particles in the air entering the tank;

　　(2) When adding flushing oil to the phase oil tank, a fueling cart with a filter should be used to filter out the contaminants in the barreled oil;

　　(3) Pause the flushing pump when replacing the filter element, taking care not to introduce impurities;

　　(4) Evacuation and sewage should be carried out regularly to ensure that the system is full and the gas and pollutants are discharged in time;

　　(5) In the early stage of flushing, the evaporation of water in the oil is very important, and there should be a window for steam to escape on the flushing oil tank;

　　(6) After the rinsing is qualified, pay attention to the protection before pumping out the rinsing oil and the pipeline before use to prevent pollutants from entering the system.

　　Fourth, the parameters of circular flushing

　　To obtain a good flushing quality, it is a very important guarantee to choose the pressure and flow rate of circulating flushing. Generally, the flushing precision of the hydraulic system of 30-40 unit circuits is NAS7 level. The flushing time is usually about 10-15 days. For the hydraulic servo system, when the required flushing precision is NAS5 level, the flushing time is even longer.

　　For those projects with relatively short construction period, it is more urgent to speed up the flushing schedule of the hydraulic system and shorten the flushing time. It can be said that it is a very difficult problem in the late stage of project construction.

　　To achieve the ideal flushing effect, the Reynolds number during flushing must be around 4000 (we know the critical Reynolds number Re(L) of smooth round-wall pipes=2200-2300). Engineering practice tells us that the carbon steel pipeline after pickling has a flushing time of 3-4 hours for each unit circuit. The cleanliness of the oil sample basically reaches NAS6-7. When the flushing circuit is shorter, the cleanliness of the oil sample even reaches NAS4. -Level

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