Selection & Replacement of Hydraulic Oil: Differences Between Various Models
1. Preface
Hydraulic oil is the "blood" of hydraulic equipment, widely used in construction machinery, machine tools, injection molding equipment, agricultural machinery, industrial hydraulic systems and other mechanical devices. The quality and model matching of hydraulic oil directly determine the transmission efficiency, seal service life, wear resistance and overall stability of hydraulic equipment. Most common equipment failures, such as excessive hydraulic oil temperature rise, valve core jamming, pipeline leakage, component wear and abnormal noise, are mainly caused by incorrect hydraulic oil model, oil aging and delayed oil replacement.
This article elaborates on the core differences, application scenarios, selection standards and standardized replacement procedures of mainstream hydraulic oil models, helping enterprise and equipment maintenance personnel select and replace hydraulic oil scientifically, reduce equipment failure rates and extend the service life of hydraulic equipment.
2. Mainstream Hydraulic Oil Models & Core Differences
At present, industrial and construction machinery hydraulic oils are mainly divided by ISO viscosity grade. The common models are 32#, 46#, 68# and 100#. Meanwhile, they are classified into HL, HM, HV and HS series according to additive formulas. These models differ greatly in viscosity, wear resistance, low-temperature fluidity and high-temperature resistance, with completely applicable scenarios.
2.1 Classification by Viscosity (32#/46#/68#/100#)
Viscosity is the core indicator of hydraulic oil, referring to the kinematic viscosity at 40℃ standard temperature. The higher the value, the thicker the oil, the weaker the fluidity, and the thicker the oil film.
32# Hydraulic Oil: Low viscosity and excellent fluidity with good low-temperature start performance. It is suitable for indoor precision hydraulic equipment, high-speed and low-pressure hydraulic systems, small machine tools and precision instrument hydraulic devices. It is the first choice for scenarios with low ambient temperature, high equipment speed and light load. Its disadvantage is unstable oil film and ordinary wear resistance under high temperature and high pressure.
46# Hydraulic Oil: The most versatile model with moderate viscosity, balancing fluidity and oil film strength. It matches most normal-temperature industrial hydraulic equipment and is the standard oil for factories. It is widely used in injection molding machines, CNC equipment, ordinary construction machinery and general hydraulic stations for normal temperature (0-40℃) and conventional load working conditions.
68# Hydraulic Oil: High viscosity with thick oil film, excellent high-temperature and high-pressure resistance. It is suitable for heavy-load, high-pressure and high-temperature working conditions, such as large excavators, cranes, mining machinery, heavy presses and outdoor high-temperature operating equipment. It is the preferred model for hydraulic systems with long-term heavy load and high-temperature environment, which can effectively avoid oil dilution, pressure attenuation and component wear.
100# Hydraulic Oil: High-viscosity special oil with poor fluidity and extreme pressure and wear resistance. It is only applicable to ultra-heavy industrial equipment, low-speed heavy-load hydraulic systems, large mining equipment and old hydraulic equipment with large gaps. It is not suitable for ordinary high-speed hydraulic systems, as it is easy to cause start jamming and excessive power loss.
2.2 Classification by Performance Formula (HL/HM/HV/HS)
Under the same viscosity, hydraulic oils with different formulas have huge performance gaps, which is the key basis for selection:
HL Ordinary Hydraulic Oil: With basic anti-oxidation and anti-rust properties and no anti-wear additives, it has the lowest cost. It is only suitable for low-pressure, low-speed and light-load simple hydraulic systems, not recommended for main industrial equipment.
HM Anti-wear Hydraulic Oil: The mainstream universal model on the market, added with high-quality anti-wear, anti-oxidation and anti-rust additives. It has stable oil film under high pressure and can effectively protect precision components such as gears, plungers and valve cores, suitable for more than 90% of industrial and construction machinery hydraulic systems.
HV Low-temperature Anti-wear Hydraulic Oil: With excellent low-temperature fluidity and low pour point, it is not easy to solidify. It is specially designed for outdoor equipment in low-temperature northern areas, winter open-air operating machinery and low-temperature warehouse hydraulic equipment.
HS Ultra-low Temperature Hydraulic Oil: High-end cold-resistant oil, suitable for special hydraulic equipment in extremely cold areas with temperature below minus 30-40℃. It has far better fluidity than HV hydraulic oil and is mostly used for special construction machinery and polar operating equipment.
3. Correct Selection Principles of Hydraulic Oil
1. According to working conditions: Choose low-viscosity (32#) for light-load and high-speed equipment, universal 46# for conventional working conditions, 68# for heavy-load and high-temperature equipment, and 100# for ultra-heavy equipment;
2. According to service environment: Select HM series for normal-temperature indoor use, HV/HS series for low-temperature outdoor use, and high-viscosity anti-wear oil for high-temperature closed working conditions;
3. Follow the equipment manual: Strictly abide by the original recommended model, and do not mix high and low viscosity oils at will;
4. Avoid random mixing: Hydraulic oils of different brands, models and formulas have different chemical components. Mixing them will cause oil deterioration, sludge generation, pipeline blockage and damage to hydraulic components.
4. Replacement Standards & Standard Procedures of Hydraulic Oil
4.1 Replacement Judgment Standards
Hydraulic oil replacement is not based on a fixed cycle, but judged by both status and working hours:
Conventional equipment: Replace every 2000-3000 working hours; Heavy-load, high-temperature and high-dust working conditions: Replace every 1000-1500 working hours; Equipment with frequent low-temperature start-stop: Replace every 1500-2000 working hours.
Replace immediately if the following conditions occur: The oil turns black, turbid, foamy or odorous; The oil is emulsified and whitened with water and impurities; The filter element is frequently blocked, with unstable system pressure and abnormal equipment noise.
4.2 Standard Replacement Steps
Step 1: Stop the equipment and cool down, wait for the hydraulic oil to cool to normal temperature, and release the residual pressure of the system;
Step 2: Drain the old oil completely, and thoroughly clean the sludge, impurities and water at the bottom of the oil tank;
Step 3: Replace all new hydraulic oil filter elements, including return oil filter and oil suction filter;
Step 4: Add new hydraulic oil of the matching model to the standard oil level of the equipment;
Step 5: Run the equipment with no load for 5-10 minutes to exhaust air from the system, and check the pressure, noise and leakage;
Step 6: Record the oil replacement time and oil model, and establish equipment maintenance records.
5. Summary of Common Misunderstandings
1. The higher the viscosity, the better: High-viscosity oil has poor low-temperature fluidity, which will increase equipment start load, cause power waste and pipeline blockage;
2. Hydraulic oil can be used for a long time: Long-term use will cause oil oxidation, deterioration and sludge generation, accelerating the wear of pump bodies and valve cores;
3. Random mixing of different oils: It is easy to cause chemical reactions, resulting in oil failure and system failure;
4. Only refueling without replacing oil: Refilling new oil cannot replace oil replacement. Impurities and oxides in old oil will continuously damage equipment.
