9 Tips You Have to Know About Hydraulic Oil

What are the main causes of media contamination in hydraulic transmission?

The reasons why hydraulic fluid is contaminated are complex, but broadly speaking, there are the following aspects.

1. Contamination by residues. Mainly refers to hydraulic components as well as pipes, tanks in the manufacturing, storage, transportation, installation, maintenance process, brought into the grit. Iron chips, abrasives, welding slag, rust flakes, cotton and dust, etc., although after cleaning, but not clean surface residue caused by hydraulic fluid pollution.

2. Contamination by intruders. Hydraulic transmission device work environment pollutants, such as air, dust, water droplets, etc. through all possible intrusion points, such as exposed piston rod, tank ventilation holes and oil injection holes into the system caused by hydraulic fluid contamination.

3. The generation of pollution. Mainly refers to the hydraulic transmission system in the work process generated by metal particles, seal material wear particles, paint stripping tablets, water, bubbles and fluid degradation after the gel caused by hydraulic fluid pollution.

How to Control the Pollution of Working Fluid?

1. Prevent and reduce external pollution. Hydraulic transmission system before and after assembly must be strictly cleaned. In the filling and discharge of hydraulic oil and the process of disassembly of the hydraulic system, should keep the container, funnel. Pipe fittings, interfaces, etc. clean. Prevent contaminants from entering.

2. Filtration. Filter out impurities generated by the system. The finer the filtration, the better the cleanliness level of the fluid and the longer the service life of the components. The appropriate part of the system should be installed in the appropriate precision filter, well and to regularly check, clean or replace the filter element.

3. Control the working temperature of the hydraulic fluid. The high working temperature of hydraulic fluid will accelerate its oxidation and deterioration, produce various substances and shorten its service life, so the maximum operating temperature of the fluid should be limited. The ideal temperature required for hydraulic systems is 15~55℃, and generally cannot exceed 60℃.

4. Regularly check and replace the hydraulic fluid. The hydraulic fluid should be regularly checked and replaced according to the requirements of the operating instructions of the hydraulic equipment and the relevant provisions of the maintenance regulations. When replacing the hydraulic fluid, clean the tank, flush the system piping and hydraulic components.

5. Waterproof and drainage. The oil tank, oil circuit, cooler pipeline, oil storage container, etc. should be well sealed and not leaking. The bottom of the oil tank should be equipped with a drainage valve. Hydraulic oil polluted by water appears milky white, and measures should be taken to separate the water.

6. Prevent air from entering. Reasonable use of exhaust valves, to ensure that the hydraulic system, especially the hydraulic pump suction line completely sealed. System oil return as far as possible from the hydraulic pump suction port, for the return of air in the oil to provide sufficient time to escape, the return pipe mouth should be beveled and extended into the tank below the liquid level, to reduce the impact of liquid flow.

What are the Factors that Affect the Quality of the Working Fluid? What are the Hazards?

1. Impurities. Impurities include dust, abrasives, burrs, rust, varnish, welding slag, flocculent material, etc.. Impurities can not only wear the moving parts, and once stuck in the spool or other moving parts, will affect the normal operation of the entire system, resulting in machine failure, accelerating component wear and tear, so that the system performance decreases, generating noise.

2. Water. The water content in the oil refers to the technical standards of GB/T1118. 1-1994, if the water in the oil exceeds the standard, it must be replaced: otherwise, not only will damage the bearings, but also make the surface of the steel parts rust, which in turn will emulsify the hydraulic oil, deteriorate and generate precipitates, prevent the cooler from conducting heat, affect the work of the valve, reduce the effective working area of the oil filter, and increase the abrasion of the oil The effect.

3. Air. If the hydraulic oil circuit contains gas, when the bubble overflow, will produce impact on the pipe wall and components to form cavitation, so that the system can not work properly, a little time will also lead to component damage.

4. Oxidation generation. General mechanical hydraulic oil working temperature is 30 ~ 80 ℃, the life of the hydraulic oil and its working temperature is closely related. When the working oil temperature exceeds 60℃, every increase of 8℃, the service life of the oil will be halved, that is, the life of 90℃ oil is about 10% of 60℃ oil, the reason is that the oil is oxidized. Oxygen and oil in the carbon and oxygen compounds for the reaction, so that the oil slowly oxidation, black colour, viscosity rise, and finally may be serious to the oxide can not be dissolved in the oil, and to brown mucus layer deposited in the system somewhere, very easy to block the components in the control oil channel, so that ball bearings, valve spool, hydraulic pump piston, etc. wear increased, affecting the normal operation of the system. Oxidation will also produce corrosive acid. The oxidation process starts slowly and when it reaches a certain stage, the oxidation speed will suddenly accelerate and the viscosity will follow a sudden rise, resulting in a higher working oil temperature, a faster oxidation process and more accumulated deposits and acid content, which will eventually make the oil unusable.

5. Physico-chemical reactants. Physico-chemical reactants can lead to changes in the chemical properties of the oil. Solvents, surface active compounds, etc. can corrode metals and deteriorate the fluid.

How can I tell if There is Water in the Hydraulic System?

Put 2-3ml of oil into a test tube, leave it for a few minutes so that the bubbles disappear, then heat the oil (e.g. with a lighter) and listen at the top of the test tube to see if there is a slight "bang bang" of water vapour, if there is, then the oil contains water.

Put a few drops of oil on a red-hot iron plate, and if a "snort" sound is made, it means that the oil contains water.

The water content of hydraulic oil is checked by comparing a faulty oil sample with a new one. A beaker (glass) of fresh oil is placed in the light and will be seen to be clear. If the oil sample contains 0.5% water it will appear cloudy and if it contains 1% water it will become like milk. Another way to check for water in hydraulic fluid is to heat a milk-like or smoky sample and after a period of time, if the sample is clear, then the fluid may contain water. If the fluid contains a small amount of water (less than 0.5%), it is usually not scrapped unless the system requirements are very stringent. Water in the fluid will speed up the oxidation process and reduce lubricity. After a period of time, the water will evaporate, but the oxidation products it causes will remain in the fluid and cause further damage later.

What Should I do if there is Water in the Hydraulic Fluid?

As water is more dense than oil, it can be left to stratify and remove most of the water.

Stir in a pan and heat the hydraulic oil slowly to 105°C to get rid of the small amount of water remaining in the oil (no air bubbles in the oil). Overseas, a filter made of paper that absorbs water but not oil is used to filter out water.

If the oil contains a large amount of water. Most of the water will eventually settle out. If necessary, a centrifuge is used to separate the oil from the water.

What is the air content in the hydraulic fluid? What is the danger of mixing air?

The volume percentage of air contained in the hydraulic medium is called the air content. The air in the hydraulic medium is divided into two types: mixed air and dissolved air. Dissolved air is uniformly dissolved in the hydraulic medium. There is no effect on the bulk elastic modulus and viscosity, while the mixed air is suspended in the hydraulic medium with a bubble state of 0.25~0.5mm in diameter, which has a significant effect on the bulk elastic modulus and viscosity. In addition, the air content is too large, there is vapor corrosion (bubble cracking at low pressure) and the "diesel effect" (high pressure air-oil mixture explosion) risk. These phenomena will lead to material corrosion.

At high air pressure, air dissolves in the hydraulic fluid. In addition, when the pressure of the working fluid is below a certain value, the hydraulic medium will boil and produce a large amount of vapour, this pressure is called the saturation vapour pressure of the medium at this temperature. Mineral oil hydraulic fluid, at 20 ℃ when the saturation vapour pressure of 6 ~ 200Pa, emulsion of the saturation vapour pressure and water is similar, 20 ℃ when the 2400Pa.

What is the standard for cleanliness of working fluids? What is the meaning?

The world standard for cleanliness of working fluids is ISO 4406, which is recognised by most industries. The standard is: the number of particles larger than 2μm, 5μm and 15μm in a known volume (usually 1mL or 100mL), expressed by the codes in Table 6-21 (other standards are also included in the table). Particles larger than 2μm and 5μm are referred to as "dust" particles. The particles most likely to cause serious consequences in hydraulic systems are those larger than 15μm. The use of 5μm and 15μm is now also in accordance with ISO standards.

What are the Different Methods of Oil Change?

●Fixed cycle oil change. This method is based on different equipment, working conditions and oil products, the use of hydraulic oil for six months, a year or 1000 ~ 2000 working hours. Although this method is widely used in the actual work, but not scientific, can not be timely detection of abnormal pollution of the hydraulic oil, when the change did not change, improper change but replaced, can not be good protection of the hydraulic system, can not be reasonable use of hydraulic oil resources.

●Field identification oil change. This method is to identify the identified hydraulic oil into a transparent glass container, and new oil comparison, do appearance inspection, through intuition to determine the degree of pollution, or in the field with pH test paper for nitric acid leaching test, in order to decide whether the identified hydraulic oil needs to be replaced.

●Comprehensive analysis of oil change. This method is to take regular samples to determine the necessary physical and chemical properties in order to continuously monitor the deterioration of the hydraulic oil and decide when to change the oil according to the actual situation. This method has a scientific basis and is therefore accurate and reliable, in line with the principles of oil change. However, it often requires a certain amount of equipment and laboratory equipment, the operation technology is complicated, the laboratory results have a certain lag, and must be handed over to the oil company for laboratory testing.

What is the Simple Practice of Judging the Quality of Hydraulic Oil and Handling Measures?

If a quality problem is found to exist that does not meet the requirements of use, the hydraulic oil must be replaced.

The following is a brief introduction to hydraulic oil quality determination methods and handling measures in four areas: inspection items, inspection methods, analysis of causes and basic countermeasures.

1. Transparent but with small black spots, see, mixed with debris, filter.

2. Milky white, see, mixed with water, separate the water.

3. Pale colour, see, mixed with foreign oil, check the viscosity, if reliable, continue to use.

4. darken, cloudy, dirty, see, pollution and oxidation, replace.

5. Compare with new oil, smell, smell, bad smell or burnt smell, replace.

6. Taste, smell, sour smell, normal.

7. Air bubbles, shake, easy to disappear after production, normal.

8. Viscosity, compare with new oil, consider temperature, mixed with foreign oil, etc., deal with as appropriate.

9. Moisture, separate the moisture.

10. particles, nitric acid immersion method, observe the results, filter.

11. Impurities, dilution method, observation of results, filtration.

12. Corrosion, corrosion method, observation of results, as appropriate.

13. Contamination, spotting method, observations, as appropriate.