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Hydraulic systems for marine machinery and maintenance guide

It is essential that operating oil (hydraulic fluid) contained within hydraulic systems is maintained in a clean condition. Failure to do so will result in poor operating performance, component failure and increased maintenance.



Dirt is the worst enemy of any hydraulic system not only the oil but the total environment in which the system is sited must be kept spotlessly clean. Hydraulic station rooms are not be used as storage areas for other items which are not associated with the plant.

Oil samples are to be sent for analysis every six months or 500 running hours whichever is sooner. When in operation, the hydraulic plant is to be regularly checked for: Disposable filter elements are to be changed every 500 to 1,000 running hours as specified by the plant manufacturer. Should any debris be found in the filter or filter chamber, the relevant Management office is to be notified. The contaminated filter element is to be placed (sealed) in a clean plastic bag ready for analysis of the debris. The Chief Engineer must fully investigate the plant in order to locate the source of the filter contamination.

Reusable filters must be opened and cleaned as per the manufacturer’s instructions. The ideal operating temperature for hydraulic oil is 50 degree C but temperatures may be between 60 degree C – 80 degree C. It must be taken into account that the higher the operating temperature the more quickly the oil ages. If overheating occurs, it is essential that the reason be found and eliminated. All weather exposed metallic couplings, connecting blocks etc. are to be well covered with DENSO tape or some similar material approved by the Management office.

Note: Normal operation of any machine strongly depends upon strict compliance with the manufacturer’s instructions provided for the machine’s use and maintenance. Hydraulic installations can be of various designs and constructions, and also, as subsystems in other machines. Their use and maintenance is subject to different operating instructions. General purpose operating and maintenance guidelines for hydraulic systems can be specified, however, these may be extended by the manufacturer or installed with additional specialised instructions for individual cases. It is necessary to fully research operational and maintenance instruction for individual plants.

Should hydraulic oil be drained from the system for maintenance or repair purposes then upon completion the system is to be bled of any trapped air. Bleed the system at the load lines as far as possible, and if possible at the highest points. Switch the directional control valves several times between their possible positions. Check reservoir tank oil levels after bleeding.


Hydraulic Hose requirement

All flexible hoses fitted to Hydraulic Equipment onboard vessels are to be of OEM or accredited Hydraulic Specialist Supply to SAE J517(pt 001-0016) Standards or equivalent. All hoses are to be supplied with certificates to confirm they are fit-for-purpose under the equipment operating parameters inclusive of: A sufficient stock of spare hoses is to be retained onboard for critical equipment such as Anchor Windlass. Stock levels and Critical Equipment is to be discussed and agreed with the vessel Superintendent. With particular emphasis on critical hydraulic hoses such as on cranes, ramps, side doors, winches, hatch covers and belt systems. Critical hoses are defined as exposed hoses located on deck equipment, the failure of which could cause an overboard pollution incident.

The interval for replacement of identified critical hydraulic hoses is reduced from 5 years to 3 years. All Non-Critical hoses remain on a 5-year renewal cycle, based on a suitable inspection and maintenance reporting regime being included within the vessels PMS.

To avoid any pollution incidents, the following procedures to be adapted.

1) Conduct a Risk Assessment of all deck equipment to identify and list the critical hydraulic hoses onboard. This RA is to be reviewed and agreed with the Fleet Superintendent.

2) The PMS must cover inspection of all hydraulic hoses, their securing arrangements and ferrules. Job cards must include checks for the following:-

i. Cracking and deterioration of the Nitrile Sheathing due to UV degradation
ii. Premature Deterioration of the Nitrile Sheathing from Coating Solvents
iii. Abrasion of the Nitrile Sheathing due to hose movement
iv. Corrosion of exposed, non stainless steel hose fittings
v. Inferior sheathing material
vi. Incorrect wire braid material - only stainless or galvanized steel is to be used.
vii. Braid material failure due to excessive use, leading to low cycle fatigue.

3) Hoses must either be procured from manufacturers or manufacturer-approved suppliers in order that the marine-suitable specification can be verified.

4) Any spare hoses kept onboard should be checked for heat deterioration of the sheathing due to incorrect storage. Spare hoses should have ends suitable capped. Spare hoses should be suitably marked date received.

5) Dates of hose replacement to be included in the PMS along with maintenance and inspection routines.

6) Ensure that hose connection ferrules are suitably protected from corrosion by applying a propriety “petro-protective” tape, such as Denso Tape. Denso tape coverings should be replaced if found dried out. It must be noted that paint on any part of the hose should be avoided as this will promote cracking due to solvent degradation of the outer sheathing

7) Manufacturer’s instructions on maintenance and inspection should also be followed.


Related Information:

Deck mooring equipment operational guideline



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