Crane Hydraulic System:Hydraulic oil complete guide

Our customers often give us feedback that the hydraulic system of marine cranes will have various problems after long-term use, and OUCO reminds you that in the daily use of cranes, you should not neglect the detection and maintenance of crane hydraulic oil. Want to know more about hydraulic oil related issues? Please read this guide.

What is the function of hydraulic oil?

Hydraulic oil is an excellent working medium. what’s more, hydraulic oil enables energy transfer, conversion and control.

Hydraulic oil can lubricate mechanical components, prevent internal rust, cool down, buffer and shock absorption, etc.

Why should I do hydraulic oil maintenance?

Hydraulic systems need very clean hydraulic oil for maximize performance.

High-quality hydraulic oil can maintain and extend the life of system components.

Marine Crane Hydraulic Power Unit
Marine Crane Hydraulic Power Unit

When should I change the crane hydraulic oil?

The deterioration of the hydraulic oil cannot be clearly seen from the outside. Therefore, the quickest way to determine: if your crane work efficiency is reduced and can not lift up well. If it happens, Well, it’s time to change the hydraulic oil inside the machine!

In addition, the following situations also need to be noted:

  1. Marine crane hydraulic oilaging, which will lead to hydraulic oil emulsification and deterioration, the aging hydraulic oil needs to be replaced in a timely manner.
  2. Marine crane hydraulic oil tank additives depletion needs to be replaced, such as antioxidants, rust inhibitors, cleaning agents, anti-foam agents, etc.
  3. The viscosity of hydraulic oil increases, the speed of hydraulic motor decreases and the movement of crane boombecomes slower.
  4. The pressure of the hydraulic system decreases and the components leak.
  5. The sound of the gear pump is abnormal, and the parts often need to be replaced.
  6. Carry out hydraulic oil test every year to ensure that the quality of hydraulic oil is within the normal range. If the test fails, it needs to be replaced.
Hydraulic oil deterioration
Hydraulic oil deterioration

Crane hydraulic oil service life?

  1. After purchase, the first replacement needs to be about six months after use, this is to prevent impurities generated in the hydraulic component break-in and solid particles in the pipeline, which will flow back to the tank with the hydraulic oil.
  2. In normal use, it needs to be replaced once a year. Of course, you can also adjust yourself according to your frequency of use. However, it should be noted that the general use period of mineral hydraulic oil should not exceed two years.
  3. Synthetic hydraulic oil can be used for up to three years if it passes the test every year.

How to properly replace the hydraulic oil?

There are many users do not follow the requirements of the hydraulic oil replacement, non-standard replacement method will lead to the failure of the marine crane. It is a mistake to simply drain the hydraulic oil tank and subsequently fill it with new hydraulic oil.

If the hydraulic oil pipe and hydraulic control valve is not clean, the internal will remain many old hydraulic oil, when we use the crane, the new hydraulic oil and old hydraulic oil mixed, the subsequent utilisation will accelerate the rate of deterioration of the new oil.

The correct oil change steps are as follows.

  1. Hydraulic oil need to ensure the use of the specified type of hydraulic oil, you can refer to the hydraulic oil guide and our related documents.
  2. Drain the hydraulic oil in the hydraulic oil tank, clean or replace the filter element, wash the oil tank and add new hydraulic oil.
  3. Remove the hydraulic oil circuit main hose, turn on the engine and run at low speed to make the oil pump work
  4. Manipulate each institution separately, and then disassemble the return hose of each working cylinder, and completely discharge the old oil in the circuit through the new hydraulic oil, until the return main hose has new oil outflow.
  5. Finally, connect the oil return hose with the oil tank, and add new hydraulic oil into the tank reach the specified position.
Cleaning Hydraulic Tank and Components
Cleaning Hydraulic Tank and Components

What should I pay attention to in the process of changing hydraulic oil?

  • During the oil change work, wear protective glasses ,turn off the motor and the main power of the equipment
  • New oil should be precipitated for more than 48h before use
  • Must use silk cloth, strictly forbidden to use cotton yarn, towels and other fiber fabric to wipe the parts
  • Post the time mark, fill in the oil change record
  • Operation site, the presence of open fire is strictly prohibited
  • Oil change process is completed on the same day to avoid temperature changes in the morning and evening

What are the hydraulic oil requirements for marine cranes?

  • The oil should has suitable viscosity and good viscosity-temperature performance
  • Good rust resistance, oxidation resistance, hydrolytic stability
  • Non-flammable, shear resistance
  • Suitability with hydraulic sealing components and hydraulic tank materials
  • Hydraulic oil with wear resistance and lubricity
  • Good anti-foaming property, so that the hydraulic oil can keep normal under continuous mechanical agitation

What hydraulic oil is used in marine cranes?

Hydraulic oil grade distinction according to the viscosity decision, marine cranes generally use 46 or 68 hydraulic oil.

46 hydraulic oil viscosity is less than 68 hydraulic oil, 46 hydraulic fluid is suitable for temperate regions, 68 hydraulic fluid is suitable for subtropical.

In addition, there are 68, 100, etc., different grades are suitable for different equipment and machines, you can choose the corresponding hydraulic fluid according to the viscosity grade recommended by the supplier.

What is the classification of hydraulic oil?

Hydraulic oil are classified into HH type, HL type, HM type, HR type and HG type

What is a hydraulic oil air cooler?

Hydraulic oil cooler products are mainly used in the return path of the hydraulic system. When working, the high temperature hydraulic oil in the hydraulic system will pass through the hydraulic oil cooler device, and the cold air will reduce the oil temperature to the working temperature required ,to ensure that the machinery and hydraulic system can operate normally.

Marine Crane hydraulic oil air cooler
Marine Crane hydraulic oil air cooler

OUCO offshore crane can be equipped with hydraulic oil air cooler according to your needs, our hydraulic oil air cooler flow pipe is arranged as shown below, so that the arrangement of the flow pipe can make the hydraulic oil flow pipe surface is larger and the cooling effect is better.

air cooler flow pipe arrangement
air cooler flow pipe arrangement

Can I mix hydraulic oil?

Try to avoid mixing hydraulic oil! If you are about to run out of hydraulic oil, it is best not to add other hydraulic oil to fill the hydraulic oil tank, different brands of hydraulic oil, they contain mostly different additives, these additives may affect each other, resulting in adverse consequences.

different hydraulic oil
different hydraulic oil

What is the difference between lubricating oil and hydraulic oil?

The main function of  lubricant oil is to reduce friction, slow down wear and prevent metal sintering.

The hydraulic oil viscosity is more important. Hydraulic oil needs to perform well at high temperatures and low temperatures, to ensure that the oil flows easily and reduces energy consumption.

In addition, they are not interchangeable. If you use hydraulic oil as a lubricant oil, it is difficult to form a protective oil film on the machine surface, which will increase the wear of the machine. Therefore, hydraulic oil is not suitable to be used as a lubricant oil replacement in your machine.


The above is the hydraulic oil guide for your reference, I believe that after reading the above content, it will be of great help to you.

Finally, if you have the need of offshore knuckle boom crane, telescoping crane and other lifting equipment, please contact OUCO today.


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