Exploring The Daily Maintenance And Management of Hydraulic Equipment on Ships

Hydraulic technology finds extensive applications in the maritime domain, encompassing various components such as steering gears, anchor windlasses, winches, and cargo handling machinery. Efficient maintenance and management of hydraulic equipment are crucial for reducing faults aboard ships. This article, starting from the level of marine engineers in China, delves into key aspects of maintenance and management of hydraulic equipment on ships from various perspectives.

Strict Control of Oil Quality and Temperature

(1) Contamination of hydraulic oil contributes to over seventy percent of total system failures. To mitigate oil contamination, attention should be paid to the following:

Hydraulic systems should undergo thorough flushing after new installation, major repairs, or replacement of severely damaged components such as pumps or motors. Particularly during dry dock periods when hydraulic steel pipes are replaced, extra vigilance is required. Observation indicates that many shipyards exhibit significant contamination issues with replaced hydraulic steel pipes. Therefore, before replacing hydraulic oil pipes, the entire system should undergo pre-operation flushing and cleaning of oil tank filters.

The contamination level of newly added hydraulic oil should be one to two grades lower than the system's requirements. Refilling should be done using dedicated clean hoses, preferably with oil filtration trucks. Hydraulic oil leaked from system leaks should not be simply filtered and reused, as it could lead to overall oil contamination.

During maintenance of hydraulic components, cleanliness is crucial. Covered with clean plastic sheets, cleaned components and disconnected pipe joints should be protected. Regular cleaning of oil tanks is essential, avoiding the use of materials that may leave impurities on the tank walls.

Impurities are inevitable in hydraulic systems due to factors such as component wear and oil oxidation. Therefore, filters must be regularly cleaned or replaced based on pressure differences (if pressure difference indicators are present).

Typically, hydraulic oil should be inspected at least once a year. Special attention should be paid if impurities are found in oil within six months of new equipment operation, as it may indicate incomplete system cleaning rather than oil deterioration.

(2) The optimal operating oil temperature for marine hydraulic equipment is between 30°C and 50°C. Coolers should be activated when the oil temperature reaches 40°C-50°C.

Summer operation should prevent oil temperatures from rising too high. The pump inlet oil temperature should generally be below 60°C. Steering gear typically operates at a maximum oil temperature of 70°C, while for cargo handling machinery, the oil temperature limit can be relaxed to around 85°C. Higher oil temperatures accelerate oxidation, leading to oil deterioration and decreased lubrication efficiency, potentially causing parts to seize due to thermal expansion.

Winter operation should avoid using oil at low temperatures, which increases oil viscosity, making pump suction difficult and potentially causing pipe or joint bursts. When the oil temperature is below 10°C, a short-term alternating start-stop pump startup method should be employed to gradually increase the temperature. Equipment should only be loaded when the oil temperature reaches 10°C to 15°C. Even for temporary use, this procedure is essential and should not be considered cumbersome. In cold weather, heaters should be activated to maintain hydraulic equipment at temperatures of at least -10°C. Starting the equipment below -10°C is absolutely prohibited.

Limiting Hydraulic Oil Leaks (External and Internal)

(1) External leaks not only result in oil loss but also environmental pollution and should be promptly rectified. External leaks often occur due to aging or damage of sealing components or corrosion and wear of shaft seals. Sealing components have a specified service life and should be replaced within a certain period. Impurities in the oil accelerate the wear of moving parts and sealing elements. Regularly checking the oil level in the working tank is necessary; a significant decrease in oil level (excluding changes due to oil temperature) indicates a system leak.

(2) Internal leaks exacerbate the reduction in the working speed of actuating components and the efficiency of devices. Under increased loads, internal leaks can cause working pressure to rise to a certain value, preventing action. Internal leakage exacerbates hydraulic oil heating (an increase in temperature of approximately 6°C for every 10 MPa pressure drop).

Increased internal leakage is due to increased wear of moving parts, resulting in increased clearance. Methods such as testing working speed, slip speed, and load testing can be used to detect internal leaks.

Key Points for Daily Operation and Maintenance of Hydraulic Components

3.1 Preventing Hydraulic Motor Overspeed

Various hydraulic motors have a maximum allowable speed. In a properly designed hydraulic system, the oil supply of the hydraulic pump does not cause the motor to overspeed. However, overspeed may occur when the motor operates under external forces such as gravity. There have been instances of motor damage due to overspeed during improper operation of anchor machinery.

3.2 Pay Attention to Abnormal Noise and Vibration.

Abnormal noise may be due to liquid noise ("cavitation" or severe hydraulic valve leakage) or mechanical noise (pump or motor damage; loose pipe or equipment fixing; poor coupling alignment, etc.). If abnormalities are detected, the cause should be identified and rectified promptly.

3.3 Ensure the Maintenance or Replacement Cycle of Components

Particular attention should be paid to lubricating specific components such as pulleys and hinge chains as required. Gearbox oil should be changed according to regulations, typically replaced every 300 hours of initial equipment use and every 1200 hours thereafter.

3.4 Hydraulic equipment that is out of use for an extended period should undergo trial operation at least once a month, with a minimum of 10 minutes of no-load operation. Simultaneously, attention should be paid to checking the insulation of the circuit.

Conclusion

Although various factors influence the performance of marine hydraulic equipment, and there is considerable turnover among ship management personnel, with a high sense of responsibility, enhanced theoretical knowledge, and practical experience in routine work, the maintenance management level of ship hydraulic equipment can undoubtedly be elevated to a new height.