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Why hydraulic oil turns black and how to prevent

Why hydraulic oil turns black and how to prevent

Essentially, 90% of hydraulic system failures in aerial work platforms are caused by problems with the hydraulic oil. If the oil is not replaced for a long time, it will turn black and the viscosity will decrease, which can directly lead to abnormal wear of various hydraulic system components such as the main pump, valve, directional control valve, oil seal, etc. Over time, this can cause excessive clearance between components, resulting in internal leakage and seriously affecting the smoothness and power of the aerial work platform’s movements.

The role of hydraulic oil: In the hydraulic system, hydraulic oil plays a major role in energy transmission, anti-wear, system lubrication, corrosion and rust prevention, and cooling.

Points to consider when choosing hydraulic oil:

(1) The hydraulic pump is one of the most sensitive components to the viscosity and viscosity-temperature performance of the hydraulic oil. Therefore, the pump’s requirements for hydraulic oil in the system are often used as an important basis for selecting hydraulic oil.

(2) System operating conditions: If the requirements for the speed of the actuator, system pressure, and actuator movement accuracy are higher, the requirements for the hydraulic oil used in terms of wear resistance and load-bearing capacity will also be higher.

(3) Tank size: The smaller the oil tank, the higher the requirements for the hydraulic oil’s oxidation stability, extreme pressure resistance, air release, and filtration.

  • Ambient temperature: Choose hydraulic oil reasonably. If there is no open flame nearby, the working temperature is below 60°C, and the load is relatively light, ordinary hydraulic oil can be used. If the equipment needs to start at very low temperatures, low-temperature hydraulic oil should be selected.

Phenomenon and reasons for hydraulic oil deterioration

  1. The hydraulic oil is too dirty and turns black.

Internal reasons: The main reason is that the oil seal ages and deteriorates after long working hours. Metal impurities such as iron chips are the main factors affecting the hydraulic oil turning black in aerial work vehicles. The wear and tear produced by the high-speed rotation of the pump, the repeated operation of the hydraulic valve spool, and the repeated operation of the oil cylinder can all produce abrasives, which will affect the quality of the hydraulic oil if not cleaned for a long time. In addition, if it is a newly purchased aerial work vehicle, a large amount of metal impurities will be generated during the running-in period. When changing the oil, all the hydraulic oil in the oil tank should be drained, and the oil tank should be wiped clean with a cotton cloth before adding new oil. If not emptied, a large amount of iron chips may remain in the oil tank, which will also cause the new oil to be contaminated and turn black.

External reasons: The main reason is that the working environment of the equipment is poor, and external pollutants enter the hydraulic oil. The poor working environment of aerial work vehicles can cause the filter element to become blocked; during the cleaning, oil changing, and maintenance processes, if dust prevention measures are not in place, impurities will be brought into the hydraulic system during operation. Therefore, diggers need to regularly check whether the hydraulic system of the aerial work vehicle is sealed and whether the breathing holes are intact; check whether the sealing of exposed parts of the hydraulic part of the equipment is intact, such as the dust seal of the oil cylinder, etc.

  1. The hydraulic oil turns white and turbid.

If the hydraulic oil turns white and turbid, solid impurities or viscous liquid impurities can be ruled out, and it can only be caused by water or air. The most reliable way is to take a sample of the hydraulic oil and send it to a testing institution for detection. The oil sample can also be dropped on a hot iron plate. If bubbles appear (water turns into water vapor at high temperature and forms bubbles), it can be determined that there is water in the hydraulic oil. If the turbidity is caused by water mixed in the hydraulic oil, the hydraulic oil should be allowed to stand for a period of time, and then the water should be removed from the bottom of the hydraulic oil tank. However, if the water content is too high and causes the hydraulic oil to emulsify, new hydraulic oil needs to be replaced. If it is determined that the turbidity is caused by air mixed in the hydraulic oil, the hydraulic system pipeline should be checked for air leakage, and the source of air mixing should be cut off.


How to prevent:

Choose the appropriate hydraulic oil. Generally, the equipment manual specifies the standards for selecting hydraulic oil, based on the type, grade, and viscosity. It is important to purchase hydraulic oil from reputable brands to avoid purchasing fake and inferior products.

Control the working temperature of the hydraulic oil during equipment use. Normally, a temperature between 50-80 degrees Celsius is acceptable, but exceeding 90 degrees can cause problems and accelerate the deterioration of the hydraulic oil.

The hydraulic oil tank must be properly sealed to prevent pollutants from entering the hydraulic system.

Regularly check the condition of the hydraulic oil, clean the filter element and oil tank, and replace contaminated hydraulic oil in a timely manner.

Pay attention to checking the sealing of pipeline connections, inspect the joints and sealing devices between the hydraulic system pipelines and components, and promptly replace any damaged parts. Tighten all pipeline connections.

The importance of hydraulic oil for aerial work platforms is self-evident. A friendly reminder: when it comes to hydraulic oil issues, oil sellers should inform their customers to raise their awareness and take preventive measures to detect problems early. If hydraulic oil deterioration occurs, it should be replaced as soon as possible.

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