Guide to Selecting Ashless Hydraulic Fluids for Optimal Lubrication

In industrial applications, hydraulic systems serve as the backbone for powering various mechanical equipment. Hydraulic oil, often referred to as the "lifeblood" of these systems, plays a crucial role in determining operational efficiency, equipment longevity, and maintenance costs. With numerous hydraulic oil products available in the market, selecting one that meets equipment requirements while balancing environmental and economic considerations presents a significant challenge for equipment managers. This article focuses on ashless hydraulic oil, analyzing the characteristics and applications of three common viscosity grades—32, 46, and 68—to provide a professional and practical selection guide for optimizing hydraulic system lubrication.

Ashless hydraulic oil, as the name suggests, is formulated without metal ash additives. Compared to traditional zinc-containing hydraulic oils, ashless variants offer several distinct advantages:

• Superior Cleanliness: The ashless formulation minimizes deposit formation during operation, effectively preventing issues such as clogged oil passages and valve sticking, thereby ensuring clean and efficient hydraulic system performance.
• Enhanced Environmental Performance: Free from zinc and other heavy metals, it reduces environmental pollution risks and complies with increasingly stringent environmental regulations, supporting sustainable development initiatives.
• Excellent Compatibility: Demonstrates good compatibility with various seal materials and metals, reducing leakage and corrosion problems caused by material incompatibility.
• Extended Service Life: With outstanding oxidation resistance and anti-wear properties, it maintains stable performance under demanding conditions, extending oil change intervals and lowering maintenance costs.

Hydraulic oil viscosity, a critical parameter in selection, measures the fluid's resistance to flow. Viscosity grades are typically denoted by ISO VG (International Standards Organization Viscosity Grade), where higher numbers indicate greater viscosity. The three common grades—32, 46, and 68—differ primarily in their flow characteristics at various temperatures.

VG 32 hydraulic oil has the lowest viscosity among the three grades, offering exceptional low-temperature fluidity. This characteristic enables quick system startup in cold environments, providing immediate lubrication protection and preventing startup difficulties and increased wear caused by high viscosity at low temperatures. VG 32 is particularly suitable for:

• Hydraulic systems in cold regions or low-temperature environments, such as refrigeration facilities, snow removal equipment, and machinery requiring frequent winter startups.
• Systems demanding high startup performance, including precision instruments and rapid-response control systems.
• Low-power hydraulic systems where smaller pumps and actuators benefit from reduced flow resistance and improved efficiency.

Note that VG 32's lower viscosity at high temperatures may provide insufficient film strength for heavy-duty or high-temperature applications, making it unsuitable for such conditions.

VG 46 hydraulic oil, with its moderate viscosity, maintains good performance across a wide temperature range, making it the most widely used grade. It balances low-temperature fluidity with adequate high-temperature film strength, suitable for most industrial hydraulic systems. Typical applications include:

• General industrial hydraulic systems such as machine tools, injection molding machines, die-casting machines, and hydraulic lifts.
• Construction machinery including excavators, loaders, and bulldozers.
• Agricultural equipment like tractors, harvesters, and seeders.
• Indoor environments with stable temperatures where it delivers consistent lubrication performance.

While VG 46's versatility makes it a popular choice, special operating conditions may require evaluation for more appropriate viscosity grades.

VG 68 hydraulic oil has the highest viscosity among the three grades, offering excellent high-temperature performance and load-bearing capacity. Under high temperatures or heavy loads, it maintains stable film strength, preventing metal-to-metal contact and reducing wear to extend equipment life. It is particularly suited for:

• High-temperature hydraulic systems in industries like metallurgy, chemicals, and power generation.
• Heavy-duty hydraulic systems such as large presses, hydraulic machine tools, and lifting equipment.
• Low-speed, high-pressure systems where higher viscosity helps maintain film integrity and reduce leakage.
• Older equipment with significant wear, where higher viscosity can fill gaps and improve sealing performance.

VG 68's poor low-temperature fluidity may cause startup difficulties and energy losses in cold environments, making it unsuitable for such conditions. Additionally, its higher viscosity increases system resistance and reduces efficiency.

Choosing the right viscosity grade requires careful consideration of several factors:

1. Operating Temperature: The primary factor in viscosity selection. Higher temperatures generally require higher viscosity, while lower temperatures need lower viscosity. Equipment manufacturers typically recommend suitable viscosity ranges in manuals.
2. System Pressure: Higher-pressure systems demand higher viscosity to ensure adequate film strength and prevent metal contact and wear.
3. Load Type: Heavy or shock loads require higher viscosity oils for better load-bearing and anti-wear properties.
4. Equipment Type and Manufacturer Recommendations: Different hydraulic equipment may have specific viscosity requirements. Always consult equipment manuals for manufacturer guidelines.
5. Environmental Conditions: Systems operating in extreme temperatures need oils with appropriate low-temperature fluidity or high-temperature stability.
6. Seal Materials: Compatibility with seal materials is crucial to prevent leaks caused by material incompatibility.
7. Operating Speed: Lower speeds generally require higher viscosity to maintain film integrity, while higher speeds benefit from lower viscosity to reduce flow resistance.

Avoid these common pitfalls when selecting ashless hydraulic oil:

• Overestimating High Viscosity: Higher viscosity isn't always better. Excessive viscosity can cause startup difficulties, energy losses, and increased oil temperatures, reducing system efficiency and lifespan.
• Ignoring Low-Temperature Performance: In cold climates, oils with good low-temperature fluidity are essential to prevent startup issues and excessive wear.
• Disregarding Manufacturer Recommendations: Always follow equipment manufacturer guidelines for optimal performance and longevity.
• Mixing Different Hydraulic Oils: Different oil types may contain incompatible additives that could degrade performance or damage the system.

Additional usage considerations include:

• Regular Oil Quality Monitoring: Periodic analysis of viscosity, acid number, water content, and contamination levels helps detect degradation early.
• Maintaining System Cleanliness: Regular filter changes prevent contaminant entry and subsequent wear or blockages.
• Avoiding Overheating: High temperatures accelerate oil oxidation and degradation, shortening service life.
• Proper Storage and Disposal: Store oil in cool, dry, ventilated areas away from sunlight and rain. Dispose of used oil according to environmental regulations.

Proper selection and use of ashless hydraulic oil are fundamental to ensuring efficient and reliable hydraulic system operation. By understanding the characteristics and applications of VG 32, 46, and 68 grades—and carefully considering factors like operating temperature, system pressure, and load type—businesses can optimize their lubrication strategies to reduce maintenance costs, extend equipment life, and enhance productivity. This guide provides valuable insights for achieving hydraulic system lubrication optimization.