10 Guidelines In Selecting The Right Hydraulic Fluid For Any Engine

Today’s hydraulic fluids serve multiple purposes. The major function of hydraulic fluid is to provide energy transmission through the system which enables work and motion to be accomplished. Hydraulic fluids are also responsible for lubrication, heat transfer and contamination control.

Hydraulic fluids are used in many applications across every industry. Examples of equipment and machinery which use hydraulic oil: Forklift trucks, automotive lift, tractors, aircraft, cruise ships, and marine industry.

Demands placed on hydraulic systems constantly change with higher efficiency and speed needs at higher operating temperatures and pressures.

Selecting the best hydraulic fluid requires an understanding of each fluid’s characteristics which include thermal stability, hydrolytic stability, low chemical corrosiveness, high anti-wear characteristics, low tendency to cavitate (form cavities or bubbles), long life, total water rejection, constant viscosity, regardless of temperature, and low cost.

Below are guidelines in selecting the right hydraulic for any engine:

1. Viscosity — Maximum and minimum operating temperatures, along with the system’s load, determine the fluid’s viscosity requirements. The fluid must maintain a minimum viscosity at the highest operating temperature. However, it cannot be so vicious at low temperature that it cannot be pumped.

2. Wear —Wear is most frequently misunderstood because wear and friction usually are considered together. Wear results from metal-to-metal contact. Minimizing metal breakdown through a protective additive is critical. In contrast, friction is reduced by preventing metal-to-metal contact through the use of fluids that create a thin protective oil or additive film between moving metal parts. Excessive wear may not be the fault of the fluid. It may be caused by poor system design.

3. Anti-wear — Zinc dithiophosphate (ZDP) is common in hydraulic fluids but ashless anti-wear fluids are being used where the metal content in any wastewater from manufacturing processes must be minimized. Different style pumps need different protection. Vane and gear pumps need anti-wear protection.

4. Foaming — When the foam is carried by a fluid, it degrades system performance so needs to be eliminated. It can be prevented by eliminating air leaks within the system but two general types of foam still occur frequently — surface foam (which usually collects on the fluid surface in a reservoir), and entrained air.

Surface foam is easy to eliminate via defoaming additives or by designing the system so it dissipates in the reservoir. However, high-concentration anti-foam agents can increase entrained air.

Fluid viscosity also influences foaming because the more viscous a fluid, the longer it can take for air bubbles to migrate through the fluid and escape.

5. Corrosion — Two potential corrosion problems exist: system rusting and acidic chemical corrosion. System rusting occurs when water carried by the fluid attacks ferrous metal parts. Most fluids contain rust inhibitors to protect against this. To protect against chemical corrosion, additives that offer stability in the presence of water to prevent breakdown and acidic attack on system metals should be considered.

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6. Oxidation and thermal stability — Over time, fluids oxidize and form acids, sludge, and varnish, which can damage system parts, like soft metals. Extended high-temperature operation and thermal cycling worsen the formation of fluid decomposition products. System design should minimize these thermal problems, and the fluid should have additives that exhibit good thermal stability, inhibit oxidation, and neutralize acids.

7. Water retention — Large amounts of water in hydraulic oil can be removed by regularly draining the reservoir. Small amounts of water can become entrained, especially if the reservoir is small. Demulsifiers are often added to the fluid to speed the separation of water. Filters can remove any remaining water from the hydraulic oil. Water should leave the oil without taking fluid or additives with it.

8. Temperature — System operating temperature varies, with the suggested maximum generally being 150°F. Temperatures of 180° to 200°F are practical, but the fluid will have to be changed more often. Systems can operate up to 250°F, but this can cause rapid decomposition of the fluid and its additives.

9. Seal compatibility — In most systems, seals are selected so the hydraulic fluid will not change their size or shape, ensuring tight fits. The fluid selected should be checked to ensure that the fluid and seal materials are compatible.

10. Fluid life and disposability — Fluids that have long operating lives bring added savings through reduced maintenance and replacement costs. Part life should also be longer with higher-quality, longer-life fluid. Longer fluid life also reduces disposal problems.

Although no fluid is ideal, it is possible to select one that is the best compromise for a particular system. This requires knowledge of the system in which a fluid will be used. The designer should know system characteristics such as maximum and minimum operating and ambient temperatures, pumps used, operating pressures and cycle, loads encountered by all components, and control and power valves types.

Three common varieties of hydraulic fluids found on the market today are petroleum-based, water-based and synthetics.

1. Petroleum-based or mineral-based fluids are the most widely used fluids today. Mineral-based fluids offer a low-cost, high quality, readily available selection.

2. Water-based fluids are used for fire-resistance due to their high-water content. They are available as oil-in-water emulsions, water-in-oil (invert) emulsions and water-glycol blends. Water-based fluids can provide suitable lubrication characteristics but need to be monitored closely to avoid problems.

Elevated temperatures cause the water in the fluids to evaporate, which causes the viscosity to rise. Occasionally, distilled water will have to be added to the system to correct the balance of the fluid. Whenever these fluids are used, several system components must be checked for compatibility, including pumps, filters, plumbing, fittings, and seal materials.

3. Synthetic fluids are man-made lubricants and many offer excellent lubrication characteristics in high-pressure and high- temperature systems. Some of the advantages of synthetic fluids may include fire-resistance, lower friction, natural detergency, and thermal stability.

Only perfectly lubricated motors and gears run smoothly, This is why LIQUI MOLY offers hydraulics tailored to suit each vehicle precisely. Whether synthetic fluids, water-based fluids, petroleum or mineral-based fluids, it is always in the highest quality.
This article is brought to you by Nomic Auto Tech. Nig. Ltd

Nomic Auto Tech. Nig. Ltd. is a top auto servicing company based in Nnewi Anambra State, which specializes in the sales and repair of automobile vehicles and sales of engine oil. Nomic Auto Tech. Nig. Ltd is one of the sole distributors of Liqui Moly.

Liqui Moly is an international brand based in Germany and is one of the leading oil refining companies in the world. It offers high-quality engine and gear oils, oil and fuel additives, auto-care products, chemical problem solvers, service products and special lubricants, complete product lines for cars, motorbikes, boats, and commercial vehicles.