Created on:2021-09-01 14:12

Fault diagnosis and maintenance of marine hydraulic equipment_ Analysis of two fault cases

Fault diagnosis and maintenance of marine hydraulic equipment_ Analysis of two fault cases

Hydraulic transmission technology has been widely used in modern ships, especially ocean going ships. Such as valve opening and closing, hatch cover, watertight door opening and closing, hydraulic steering gear, hydraulic cargo winch, windlass and automatic mooring device, etc.

Common faults of ship hydraulic equipment include: action fault (such as abnormal startup, too slow or unable action of actuator, significant reduction of actuator speed under load, etc.); Pressure failure (e.g. the pressure fails to meet the specified requirements, unstable pressure or regulation failure, excessive pressure fluctuation, etc.); Noise and vibration; The oil temperature is too high; Oil contamination, etc.

① The hydraulic steering gear cannot return to the rudder when one side is full. The steering gear of "SC" wheel is a hydraulic valve controlled and double ram steering gear, and a is the hydraulic control schematic diagram of the steering gear. When the ship passed through a sea area, the officer on duty found that the ship under normal navigation suddenly and quickly deviated from the set route, the bow deflected towards starboard, the rudder angle indicator increased continuously, and finally stopped at the full rudder position, the whole ship tilted seriously to the right, and the GPS route deviation alarm gave an alarm. In this case, the officer on duty shall immediately switch to another standby steering gear and make an emergency stop. At the same time, he shall report the relevant situation to the master and engine room. When it is confirmed that the standby steering gear can be used normally and the steering gear system operates normally, he shall start the main engine to correct the heading. Fortunately, there were few ships in the Western Zhou Dynasty at that time, which did not cause serious consequences. In view of this fault, the cabin personnel immediately repaired and analyzed the problem steering gear, and found that the spring in the right return of the reversing pilot valve controlled by the solenoid coil was broken, resulting in the broken metal debris entering the control reversing valve, resulting in the wear and seizure of the valve core and valve seat, which could not be reset, resulting in the above emergency situation of full rudder on one side. Then, what is the reason for the fracture of the return spring? Through the search and careful analysis of the cabin personnel, it is found that the following problems in the steering gear system lead to the above faults:

a. The hydraulic oil is used for a long time and is not renewed according to the requirements of the manual, resulting in dirty and deterioration of the oil;

b. During the maintenance and adjustment of relevant parameters of the autopilot by the electrical engineer of this voyage, the course of the autopilot deviated from the automatic correction due to incorrect adjustment, and the insensitive area became smaller, resulting in excessive action times of the steering gear change-over valve in unit time, resulting in fatigue fracture of the return spring of the change-over valve;

c. The poor heat dissipation of the hydraulic oil in the return tank causes the oil temperature to be too high, resulting in serious mutual wear of the moving elements and deterioration of the hydraulic oil.


② The hydraulic motor of the windlass is too slow and powerless. The "SR" ship windlass is a hydraulic windlass manufactured by Mitsubishi company. This type of windlass adopts a manual three position four-way valve as the reversing control valve to change the running direction of the windlass; The variable displacement pump is used to control the flow into the hydraulic motor to control the operating speed of the windlass.

When the ship was sailing at an anchorage, the boatswain found that the anchor lifting speed of the windlass was slow and weak, and the noise emitted by the hydraulic pump was large. After knowing the situation, the chief engineer shall assign the third engineer to find the fault and repair it. According to the phenomenon described by the boatswain, the third engineer thought that the flow was too small due to the blockage of the fine filter in front of the hydraulic pump, resulting in the low speed of the hydraulic motor of the windlass and the slow lifting speed of the anchor. Therefore, the fine filter was cleaned. After cleaning, when the system gas drive operation was carried out, only the reversing operation handle was placed in the middle position, and the hydraulic pump was started for gas drive before it was delivered for use.

The ship sailed to the north channel anchorage of the Yangtze River Estuary and anchored. When the anchor chain was tightened, the hydraulic motor was slow and weak. With the extension of operation time, this phenomenon became more and more serious, and finally the anchor chain could not be tightened. What causes this phenomenon? During the subsequent maintenance, the maintenance staff found that there was a lot of foam in the hydraulic fluid and the oil smelly and darkened. Through further analysis, we can know the causes of this fault: first, the three pipe wheel only places the reversing operation handle at the middle position for system air drive operation, resulting in incomplete discharge of system air. The mixing of hydraulic oil and air makes the vacuum at the inlet of hydraulic pump too small, resulting in insufficient flow and low pressure. With the extension of service time, the mixing of hydraulic oil and air intensifies, It makes the hydraulic pump difficult to suction and discharge, and the flow and pressure become smaller and smaller; Second, the long-term use of hydraulic oil without replacement according to the requirements of the manual is also one of the reasons for this fault. In view of this situation, the cabin personnel first replace the hydraulic oil of the whole system, thoroughly clean the system to avoid the mixing of old and new oil, and then carry out the air displacement operation of the system. First place the operating handle in the middle position for air bleeding, and then carry out forward and reverse rotation repeated operation under the condition of low load of the hydraulic motor, starting from the air bleeding of the hydraulic pump and hydraulic motor, Until there is no air in the system. After such maintenance and treatment, the whole system fully meets the standard of normal use.

③ The common characteristics of the two faults can be summarized as follows.

a. The cabin personnel failed to maintain the hydraulic equipment and system in place and failed to carry out corresponding maintenance according to the requirements specified in the manual.

b. The low quality of maintenance personnel, weak sense of responsibility in the process of operation and management, and poor ability to analyze and solve faults in case of faults are the root causes of hydraulic equipment faults. Based on the above analysis, the following analyzes the measures to reduce the failure of ship hydraulic equipment from the maintenance and management of ship hydraulic equipment.

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