Most industrial hydraulic systems exist in unclean atmospheres and are frequently pushed for required production. Ensuring reliability in the equipment is critical. In preventing hydraulic system damage or equipment degradation, there are three important issues to consider:

• Using a quality lubricant with good physical and chemical stability;
• Implementing a good filtering process to maintain cleanliness levels; and
• Maintaining a routine monitoring program to detect problems early.

When selecting a hydraulic fluid, it is important to determine which characteristics that would be most desirable for your system. Hydraulic fluids contain various additives such as anti-wear or fire resistance additives, rust and oxidation inhibitors and viscosity improvers. The hydraulic fluid used must be compatible with the materials in the hydraulic system, such as sealing materials, plastics, and metals. The fluid must also meet the equipment manufacturer’s recommendations and specifications. In certain applications, safety issues are extremely important. Safety can be greatly improved by using a water based hydraulic fluid. Where there is a potential fire hazard, the use of an aqueous- based lubricant will allow optimum fire protection.

Implementing a good filtering process in a hydraulic system is essential. The majority of hydraulic system failures are a result of particulate contamination. Hydraulic systems are affected by small particles as well as large ones. Particles are generated by a variety of sources including: wear metals, ingested dirt, debris and faulty components, such as seals or gaskets. Before implementing a filtering process in a hydraulic system, the equipment manufacturer should be consulted. It is also a good idea to consult with the lubricant provider. Because certain filters can remove performance additives and small amounts of water, their use could damage the unit.

Whether you are using a petroleum- based, synthetic, or aqueous- based hydraulic fluid, proper hydraulic fluid maintenance is essential. With the hydraulic fluid coming in contact with all system components, lubricant monitoring in hydraulic systems can give an excellent indication of the condition of all the hydraulic system components. Minor problems can be detected through lubricant analysis before they lead to costly failures. The following tests are often used in describing the properties of hydraulic fluids.

Viscosity

Viscosity is the most critical property of any hydraulic fluid. Viscosity is a measurement of a fluid’s resistance to flow. Fluid viscosity is directly affected by temperature and pressure in the system. As the temperature increases, the viscosity decreases; as pressure increases, the viscosity increases. Changes in viscosity by either increasing or decreasing it can indicate contamination or degradation.

Water Content

Water content of a hydraulic fluid is important, whether the lubricant is aqueous based or otherwise. Too much water will reduce the fluid’s viscosity, thus impairing its ability to lubricate properly. Too little water in an aqueous based lubricant can allow the fluid to lose it fire resistance capability.

Total Acid Number

Total acid number monitors the level of organic acids produced from the oxidation of the oil. All systems in which an extended drain interval is contemplated or in which the potential exists for acidic contamination should be monitored for an increase in acidic

Foaming Characteristics

Foaming characterisitcs can be determined at specified temperatures. This allows a determination of the foaming tendency and the stability of the foam. The tendency of oils to foam can lead to inadequate lubrication, thus resulting in mechanical failure.

Specific Gravity

Specific gravity is the ratio of the mass of a given volume of material at a specific temperature to the mass of an equal amount of water at the same temperature. An increase in specific gravity may indicate the presence of contaminates or oxidized materials.

Flash, Fire Point

Flash and fire point are relevant to safety. The flash point of a lubricant is the point at which the oil has released enough vapors to ignite when an open flame is applied to it. The fire point of a lubricant is the point at which vapors are released rapidly enough to support combustion. For safety purposes, the higher the flash or fire point, the better.

Spectrometry

Spectrometric analysis measures elements that that indicate contamination, wear, and additive depletion. The main focus of this technology is to trend the accumulation of small wear metals and the elemental constituents of additives, and to identify the possible introduction of contaminates.

Particle Counting

Particle counting will track the numbers of particles of various sizes, without regard to their composition. Excessive fluid particulate contamination is a major cause of hydraulic pump failure.

Establishing and maintaining a hydraulic system at optimal running condition involves many important decisions. Finding the best possible lubricant and filters to provide the cleanliness levels required can demand detailed research. Implementing an effective routine monitoring program is essential in the detection of contamination and degradation in the system. Detecting problems at an early stage can greatly impact the performance of the equipment and minimize down time. A combination of knowledge concerning the equipment, lubricant and analysis data will ensure the utmost protection of your hydraulic system.

as seen in:
Lubricants World
November, 1997