Created on:2021-08-30 14:11

Fault diagnosis and maintenance of marine hydraulic equipment_ Control measures of fin stabilizer oil pollution

Fault diagnosis and maintenance of marine hydraulic equipment_ Control measures of fin stabilizer oil pollution

(1) Control measures of oil pollution in hydraulic system

① Seamless steel pipe shall be used as much as possible, and seamless welded pipe shall be used less or not, because seamless steel pipe is relatively clean. Threaded connection between steel pipes shall be avoided as far as possible.

② The hose shall be minimized unless moving parts are connected, because the rubber particles on the inner wall of the hose may fall off and form serious pollution when the hose is bent frequently. If hoses must be used, rubber hoses lined with Teflon shall be used as far as possible.

③ Filter is the most common and effective purification device to prevent particle pollution in the hydraulic system. In the hydraulic system, in addition to installing filters at the oil suction and discharge ports and oil return circuits, it is best to set protective filters in front of important components. The filter accuracy shall be reasonably selected according to the pollution resistance of hydraulic components and the sensitivity to solid pollutants. Too high filtration accuracy is easy to reduce the working life of the filter and increase the resistance and maintenance workload of the system; The low filtration accuracy will not meet the requirements of hydraulic components and will be in vain. The filter accuracy selection shall consider the components in the system that are most sensitive to contaminated particles, the whole hydraulic system and the installation position of the filter. Refer to table 1 below for the requirements of hydraulic components on filtering accuracy, and refer to table 2 below for the requirements of each oil circuit of hydraulic system on filtering accuracy.

Table 1 requirements of hydraulic components for filtration accuracy

Hydraulic components



液 压 元 件




















Table 2 requirements for filtering accuracy of each oil circuit of hydraulic system




























Different hydraulic systems or different oil circuits of the same hydraulic system have different working pressures and different requirements for filtration accuracy. The relationship between working pressure and filtration accuracy is shown in the table below.


Relationship between working pressure of hydraulic system and filtration accuracy
































In addition, the filter with pressure indicator can be selected to show the blockage degree and serve as the basis for replacing the filter element. Some filters also provide a differential pressure switch to provide signal or protection when the filter is extremely blocked.

④ In a particularly harsh environment with dust, a pressurized oil tank can be used, which can prevent dust and moisture from entering.

⑤ Welded oil tanks, inner walls of pipes, castings, threads and elbows are important sources of pollutants. Before installing the system, the above parts must be thoroughly cleaned, the flash, burr and gravel of the oil tank, all pipes and components must be removed, and cleaned with gasoline, and then the inner and outer surfaces of the oil tank, pipes and components shall be wiped with clean fabric that is not easy to remove fibers. If possible, the oil tank, pipes and components shall be washed with new hydraulic oil used by the system. Before the installation of components, the bench test or test run must be carried out, the components shall be loaded, high-pressure running in and cleaned, and the "dry assembly" method shall be adopted, that is, dry compressed air shall be used before assembly to confirm that all components meet the pollution requirements before installation. When assembling the hydraulic system, pay attention to remove the weld beading and welding slag at the pipe connection to prevent impurities from remaining in the system. The oil tank shall be thoroughly cleaned before installation, and the inner wall of the oil tank shall be specially treated to prevent the system from being polluted by paint and rust, and the oil tank shall be equipped with effective dust-proof device. In addition, the oil return circuit of the main pump of the fin stabilizer hydraulic control system is separated from the common oil return circuit and directly connected to the oil tank, which brings two great benefits: first, it eliminates the impact of the oil return pressure on the hydraulic pump and avoids the damage of the pollutants in the oil to the "heart" of the hydraulic pump; The second is to make the oil drainage of the hydraulic pump cavity more smooth, which is conducive to the cooling of the pump body. Two techniques are adopted in the box structure: one is to use two filter screens to filter out pollutants and bubbles mixed into the oil; Second, the bottom of the tank is designed as an inclined bottom, the side of the oil return port is lower than the side of the oil suction port, and a flow guide groove is set, as shown in Figure J. In this way, even if the pollutants on the oil return port side are stirred, they will not enter the oil suction port.

⑥ If all cleaned pipes and components are not used immediately, their ports shall be sealed and stored.

⑦ The new oil is preferably injected into the oil tank through a filter (20 ~ 25pm). After 24 ~ 72h, the pipes and hoses are directly connected (jump off the servo valve and other hydraulic components), start the pump to filter new oil and flush the hard and hoses, connect the servo valve and hydraulic components after 24 ~ 72h, and then start the system. Hydraulic servo system used in filtration cleaning process 5 μ M filter, the filter element should be replaced several times. For the hydraulic control system of ship equipment, according to the particularity of the ship, the refueling device with certain filtering accuracy can be added or the oil filter with refueling port can be selected. For large capacity oil tank, its refueling device can be designed as a fixed type with oil filter and integrated with hydraulic control device, as shown in Figure K. The oil filler l of small and medium capacity oil tank adopts the single mobile type without oil filter, but the oil filter of hydraulic control device oil tank is required to be equipped with oil filler, as shown in Figure L. In this way, it can not only facilitate refueling, but also leave no open oil port that can be directly intubated and dumped, which can effectively control the artificial pollution of oil. In addition, if the oil needs to be supplemented due to leakage, the hydraulic oil of the same brand should be added.


⑧ The cleanliness of oil samples shall be tested regularly (according to manufacturing regulations). When replacing hydraulic components or overhauling the oil circuit, open the oil circuit. Filter the oil and check the cleanliness of the oil before restarting the machine after completing the task, and then run the system after it is qualified.

⑨ Strengthen pollution control during use and maintenance. During use, the system shall be frequently inspected and maintained, and the faults of the hydraulic system shall be eliminated in time to prevent the system from working with faults. Replenish and replace the hydraulic oil regularly to prevent the oil level in the oil tank from being too low. The bubbles suspended in the oil in the oil tank can be removed through the filter screen before entering the oil suction port of the hydraulic pump. The position of the filter screen in the oil tank should have an inclination of 20 °, with the highest efficiency, and the denser the filter screen, the higher the degassing efficiency. Clean the oil tank and pipeline regularly. The new oil can be added to the oil tank only after precipitation filtration. When adding to the oil tank, use the oil filter to reduce the initial degree of oil pollution. The oil shall be checked regularly. If the oil needs to be changed thoroughly, not only the oil in the oil tank, but also the oil in the pipeline and circuit shall be drained. Frequent inspection and cleaning of the filter is an important work, and the filter or filter element shall be replaced if necessary. In order to prevent air from entering the system, the sealing of the hydraulic cylinder and pipeline connection parts shall be checked frequently, the leakage shall be solved in time, and the air in the system shall be removed. In the process of maintenance, there shall be a strict management system for the cleaning of components to avoid bringing in new pollutants. Through the measurement of oil pollution and the control measures taken, the oil pollution caused by solid particles, moisture and air in the system can be effectively prevented.

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