How to Select Hydraulic Oil | 6 Types & 10 Selection Tips

Anyone engaged in hydraulic equipment maintenance knows clearly that 80% of hydraulic system failures stem from incorrect hydraulic oil selection.

The common problems are failing to choose oil according to national standards or mismatching viscosity grade with working conditions. Minor issues cause abnormal equipment wear and reduced operating efficiency. Severe cases lead to pump burnout and unexpected shutdowns, resulting in production delays and high maintenance costs.

Many technicians regard hydraulic oil as a simple consumable and pick it casually. In fact, hydraulic oil is the blood of the hydraulic system. The right oil doubles equipment service life and cuts operation costs. The wrong oil brings endless faults and frequent repairs.

This article thoroughly explains the complete logic of hydraulic oil selection. It covers 6 mainstream hydraulic oil types with national standard specifications and 10 core selection tips. You can follow this guide directly for daily equipment maintenance.

1. 6 Main Types of Hydraulic Oil & National Standards

Most industrial hydraulic oils follow GB/T 11118.1-2011. Special flame-resistant types adopt exclusive standards. Below are the classification, key parameters and application scenarios.

1.1 L-HL Hydraulic Oil

Basic general oil with rust and oxidation resistance.

Viscosity index ≥ 80.

Suitable for low-pressure light-duty equipment below 7 MPa, ideal for indoor normal temperature working conditions.

1.2 L-HM Anti-Wear Hydraulic Oil

The most widely used anti-wear hydraulic oil in industry.

Ordinary grade: viscosity index ≥ 85.

High-pressure grade: viscosity index ≥ 95.

Perfect for medium and high-pressure piston pumps and gear pumps above 7 MPa.

1.3 L-HV Low-Temperature Hydraulic Oil

Wide temperature adaption type.

Viscosity index ≥ 140, pour point down to -39°C.

Best choice for cold regions above -30°C and outdoor equipment with large temperature differences.

1.4 L-HS Ultra-Low Temperature Hydraulic Oil

Professional oil for extremely cold areas.

Viscosity index up to ≥ 150, pour point as low as -45°C.

Designed for harsh environments below -30°C.

1.5 L-HG Hydraulic & Way Lubricant

Dual-purpose oil for hydraulic system and machine tool guide rail.

Optimized stick-slip performance, effectively solves guide rail crawling and jitter for integrated machine tool lubrication systems.

1.6 L-HFC Fire-Resistant Hydraulic Oil

Comply with GB/T 21449-2020.

Water-glycol formula with water content ≥ 35%.

Applied in high-risk flammable scenarios such as steelmaking, casting and forging near open fire.

2. 10 Core Tips for Hydraulic Oil Selection

Master these key points to avoid wrong selection and hidden equipment troubles.

2.1 Select Oil According to System Pressure

Below 7 MPa: Choose L-HL

7–14 MPa: Choose standard L-HM

Above 14 MPa: Use high-pressure L-HM, L-HV or L-HS

2.2 Match Hydraulic Pump Type

Vane pump, gear pump and piston pump have different anti-wear requirements.

Never use low-pressure L-HL oil for high-pressure piston pumps.

2.3 Viscosity Matches Equipment Speed

1500–5000 r/min light-duty high-speed equipment: No.15 / No.22

Medium-low speed heavy-duty equipment: No.68 / No.100

2.4 Determine Oil Type by Ambient Temperature

Indoor normal temperature: L-HL / L-HM

Cold outdoor large temperature difference: L-HV

Extreme cold climate: L-HS

2.5 Use Fire-Resistant Oil Near Open Fire

For metallurgy, casting and high-temperature flammable environments, replace mineral oil with L-HFC flame-resistant hydraulic oil for safety.

2.6 Machine Tool Guide Rail System Choose L-HG

For machine tools combining hydraulic and guide rail lubrication, L-HG specially eliminates crawling and unstable operation.

2.7 Anti-Rust Performance for Humid & Coastal Areas

For seaside and high-humidity working conditions, select oil passing B-phase liquid rust test to prevent pipeline and valve corrosion.

2.8 Pay Attention to Demulsibility

For working conditions with water mixing risk, control demulsification time within 30 minutes as national standard required.

2.9 Air Release Value for High-Pressure & High-Speed System

Smaller air release value reduces cavitation risk and greatly extends pump and valve service life.

2.10 Do Not Mix Different Types or Viscosity Grades

Mixing different hydraulic oil types or viscosity grades will cause additive failure, system failure and permanent equipment damage.

3. Conclusion: Matching Is More Important Than Expensive

Hydraulic oil selection is not about choosing the most expensive one, but the most suitable one.

Follow national standards, match system pressure, pump type, rotating speed, temperature and actual working conditions. Proper hydraulic oil selection reduces 80% of equipment faults, cuts downtime loss and lowers maintenance costs, becoming the most cost-effective investment for factories and equipment maintenance.

FAQ

Q1: Why do most hydraulic system failures relate to hydraulic oil?

Statistics show 80% hydraulic faults are caused by wrong oil selection, inferior oil quality or improper mixing.

Q2: What is the difference between L-HL and L-HM hydraulic oil?

L-HM adds strong anti-wear additives for medium and high-pressure systems, while L-HL only provides basic rust and oxidation resistance for low-pressure equipment.

Q3: Can different brands of the same viscosity hydraulic oil be mixed?

It is not recommended. Different brands have different additive formulas, which may cause layering, failure and system abrasion after mixing.