（1） Select type based on equipment requirements
Normal working condition: Choose HL or HM type (HM type is applicable in most parts of China) 1;
Low temperature environment: HV (-25 ℃~-40 ℃) or HS (≤ -45 ℃) 12;
Precision machine tool: Choose HG type 2;
High temperature/flammable environment: synthetic or fire-resistant hydraulic oil (such as phosphate ester type) is preferred.
（2） Principle of viscosity selection
Pump type adaptation:
Blade pump: recommended viscosity of 25-68mm ²/s at 40 ℃;
Piston pump: 16~47mm ²/s;
Gear pump: 19~42mm ²/s3.
Temperature adaptability:
Choose high viscosity oil for high-temperature and high-pressure systems, and low viscosity oil for low-temperature and low-pressure systems;
Ensure that the viscosity during low-temperature start-up is ≤ the maximum start-up viscosity of the pump, which is 34.
（3） Other key indicators
Cleanliness:
Adopting ISO4406 or NAS1638 standards, high-precision systems need to be equipped with filters below 5 μ m.
Economy:
Avoid focusing solely on price, and consider both maintenance costs and lifespan (such as HM oil being expensive but extending equipment lifespan).
compatibility:
Compatible with sealing materials, coatings, etc. to avoid chemical reactions that may cause oil degradation.
（4） Maintenance suggestions
Regularly check the moisture content of the oil (judged by visual turbidity or "burst test") 5;
Control the oil temperature at 30-65 ℃ (applicable to 46 # oil), and accelerate oxidation at high temperature for 45 degrees;
Thoroughly clean the system before first use to avoid contamination by impurities.
