Key Roles of Hydraulic Fluids: Ensuring Efficient Operation & Preventing Failure

Hydraulic fluids are key components of hydraulic pumps and motors. The wrong type of fluid or dirty fluid results in inefficient operation and, eventually, catastrophic failure.

Knowing if you have the correct fluid is essential. But how can you know?

The proper fluid depends on the type of pump or motor, its operating temperature maximum, and the material from which the pump seals are constructed.

Hydraulic Fluid

Hydraulic fluid (or hydraulic oil) serves critical functions within a hydraulic system, including the following:

• Transmitting energy
• Dissipating heat
• Preventing corrosion
• Lubricating components

Why Hydraulic Fluid is Important for Pumps

Poor hydraulic fluid choice can cause multiple system problems, including the following:

• Excessive heat generation
• Formation of sludge and varnish
• Erosion and excessive surface wear
• Reduced component life
• Significantly reduced system efficiency

If your pump or motor suffers from any of these issues, it’s time to look into whether a different hydraulic fluid is needed.

Key Properties of Hydraulic Fluids

When choosing or replacing the hydraulic fluid is needed, understanding the key properties of these fluids is indispensable. The key characteristics include the following:

• Viscosity
• Lubrication
• Thermal properties
• Flammability
• Stability
• Foaming

Viscosity

A fluid’s viscosity is its resistance against the flow. When the viscosity is too high, inefficiency plagues the system. As a result, components receive too little lubrication, resulting in damage. On the other hand, when viscosity is too low, lubrication is also poor, and the fluid fails to transmit energy efficiently.

Lubrication

Lubrication protects surfaces and components within the system by preventing metal-on-metal rubbing. Specific hydraulic systems need fluid with additives to properly lubricate internal parts.

Thermal Properties

Hydraulic motors and pumps have different operating temperatures, an important issue for equipment used outside where temperatures fall below freezing. The appropriate fluid can dissipate the heat generated by friction in the appropriate weather conditions.

Flammability

Some hydraulic systems must be used in explosive or flammable areas. For these situations, hydraulic fluids need high flashpoints. Flashpoints are the temperatures where hydraulic fluid can ignite in the air. Hydraulic fluids with non-petroleum bases and heavy water content are the best choices where flammability can be problematic.

Stability

The hydraulic fluid must be non-volatile. In addition, it needs to be both physically and chemically stable even with extreme pressure fluctuations, wide temperature ranges, and storage over long periods.

Foaming

Foaming happens when hydraulic fluid expels trapped gases. It often occurs because of an increased system temperature and the loss of hydraulic fluid through gas releases.

Types of Hydraulic Fluid

Hydraulic fluids come in three types: water-based, petroleum-based, and synthetic. The three kinds have unique characteristics that make them ideal for specific hydraulic systems.

Water-based

Water-based is the original hydraulic fluids. Though water is not as effective a lubricant as other fluids, it is perfect for situations where a fire is a real possibility. Water-based fluids are also less expensive versus other types.

Petroleum-based

Petroleum-based fluids are more common than water-based lubricants and cost less versus other synthetic fluids. There are three main types of petroleum-based fluids:

• Group I: produced from solvent neutral mineral oils
• Group II: comprised of hydroprocessed base oil
• Group III: comprised of hydrocracked base oils
• The higher base oil groups offer superior corrosion resistance.

Though additives make up just 1% or less of petroleum-based fluids, they significantly impact hydraulic fluid performance. Additives include antioxidants, anti-wear components, foam inhibitors, viscosity modifiers, and rust inhibitors.

Synthetic

Synthetic hydraulic fluids are designed to enhance fluids with high-performance properties. They work very well in flammable conditions. They are the most expensive, but their properties allow top-flight performance in extreme temperatures and under high pressure.

In Summary

Unless a pump or motor is deployed in a very flammable environment, either petroleum-based or synthetic fluids are good options. The fluid viscosity heavily depends on both temperature and pressure. Low-temperature working conditions require lower-viscosity fluid. In addition, fluids must be chemically compatible with the pump seals. When selecting synthetic hydraulic fluids, checking the compatibility with seals is exceptionally important.

Hydraulic pumps and motors require the correct fluids to remain lubricated and function in outdoor temperatures. By properly selecting fluid and maintaining it, you can keep your hydraulic pumps and motors working strong.

Questions on your hydraulic equipment? Contact Servo Kinetics in Ann Arbor Michigan. We are a full-service hydraulic repair, inspection and rebuild facility that delivers the highest quality standards at the lowest possible cost. If you need help with industrial hydraulic repair services including Vickers classic factory rebuilds and Beach Russ, are looking for reverse engineering services, or new pumps and motors, we can help. Call and speak to a Specialist today!