Hydraulic failures? The root cause is often a tiny oversight

During the operation of hydraulic systems, oil leakage and unstable output are common issues that often leave operators helpless, eventually forcing them to make do with subpar performance. In reality, however, most hydraulic systems leave the factory in perfect condition. Problems typically emerge about a year after commissioning – due to the working environment, the hydraulic fluid gradually degrades. Replacing the fluid in time can restore performance, but many engineers switch to a "near-usable" oil only to see failures recur shortly afterwards, sometimes even causing equipment damage. Clearly, the root cause often lies not in the system itself, but in the incorrect selection of hydraulic oil.

Hydraulic oil is an essential working medium for any hydraulic system, and different systems have vastly different performance requirements. Take construction machinery as an example: loaders operate under harsh conditions with heavy loads and high oil temperatures, so they typically require high-grade anti‑wear hydraulic oils such as L‑HM32 or L‑HM46. In low‑temperature environments, low‑pour hydraulic oils like L‑HV32 or L‑HV46 are recommended. For sanitation vehicles, the hydraulic system is significantly affected by seasonal changes – L‑HM46 is preferred in summer, L‑HM32 in winter, and when temperatures drop below ‑20°C, oils with even better low‑temperature performance are needed.

Youjiaxin Hydraulic Technology (Dongtai) Co., Ltd., located in Yancheng, Jiangsu, produces products widely used in construction machinery, loaders, sanitation vehicles, and more. To address the high‑impact, heavy‑load conditions of loader applications, Youjiaxin adopts heavy‑duty designs and high‑performance seals in the design and manufacture of its cylinders, effectively handling high pressure and shock loads. However, even with excellent hardware quality, improper hydraulic oil selection can still lead to system leakage, unstable output, and even equipment damage.

Common hydraulic oils fall into three main categories: mineral‑oil‑based, emulsion‑type, and synthetic‑type. Each category includes various grades suited for different applications. Detailed descriptions follow:

I. Mineral‑oil‑based hydraulic oils
These are refined mineral oils with various functional additives and are the most widely used.

1. Low‑temperature hydraulic oil – Formulated with additives to improve viscosity‑temperature characteristics, suitable for high‑pressure systems at ambient temperatures as low as ‑40～‑20°C. These are commonly used in winter for sanitation vehicles in northern regions and construction machinery operating outdoors.

2. General‑purpose hydraulic oil – Made from refined mineral oil with anti‑oxidation and anti‑rust additives, intended for indoor medium‑ and low‑pressure systems in general equipment.

3. Anti‑wear hydraulic oil – Enhanced with anti‑wear additives, widely used in hydraulic systems of construction machinery, vehicles, and other equipment. Loaders, excavators, cranes, and similar construction machinery typically use this type.

4. Total‑loss system oil – Lightly refined mineral oil with poor anti‑oxidation and anti‑foam properties, mainly used for lubrication. It can only serve as a substitute for low‑pressure systems with low demands.

5. High‑viscosity‑index hydraulic oil – Formulated with additives to raise the viscosity index above 175, suitable for low‑temperature systems with special viscosity‑temperature requirements, such as CNC machine tools or systems containing bronze or silver components.

6. Turbine oil – Deeply refined mineral oil with enhanced anti‑oxidation and anti‑foam properties. While designed for steam turbines, it can be used as a substitute in general hydraulic systems.

7. Hydraulic way oil – Based on anti‑wear hydraulic oil with additives to improve stick‑slip characteristics, suitable for systems in machine tools where both hydraulic and way lubrication are combined.

II. Emulsion‑type hydraulic oils
These are emulsions of oil and water (or water phase), featuring fire resistance, making them suitable for applications requiring flame retardancy.

1. Oil‑in‑water emulsion (high‑water‑content fluid) – Fire‑resistant, with good viscosity‑temperature characteristics and some rust protection, but poor lubricity and prone to leakage. Suitable for systems with large oil usage, significant leakage, and fire‑resistance requirements.

2. Water‑in‑oil emulsion – Combines the anti‑wear and anti‑rust properties of mineral oils with fire resistance, suitable for medium‑pressure systems that require flame retardancy.

III. Synthetic hydraulic oils
These use chemically synthesized base oils, offering strong performance tailorability for special applications.

1. Water‑glycol fluid – Fire‑resistant, with good viscosity‑temperature characteristics and corrosion resistance, operating range ‑20～50°C. Ideal for medium‑ and low‑pressure systems where fire resistance is required.

2. Phosphate ester fluid – Fire‑resistant, excellent in lubrication, anti‑wear, and anti‑oxidation properties, with a wide operating range of ‑20～100°C. However, it is toxic and should be reserved for high‑pressure precision hydraulic systems that demand fire resistance.

Proper oil selection is the key to ensuring long‑term, stable operation of any hydraulic system. Whether it is construction machinery like loaders and excavators, municipal sanitation vehicles, or the various cylinder systems supplied by Youjiaxin in Yancheng, Jiangsu, the right hydraulic oil must be matched according to system type, working pressure, ambient temperature, and fire‑protection requirements. Only then can we eliminate the root causes of leakage and unstable output, and avoid the greater losses that come from "making do."