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This chapter discusses the deterioration and maintenance of hydraulic fluids. Reliability surveys reveal the majority of service problems are due to contamination. Approximately 80%–90% of all faults in hydraulic systems, abnormal wear, valve malfunctioning, etc. may be ascribed to particulate contamination and inadequate filtration of the hydraulic fluid. One should keep a regular check of the particle count to ensure that the filters are working effectively. Oil level, service temperature and filters should be checked at regular intervals. Water absorbing filter elements should be used to remove relatively small volumes of water. The chapter also describes the various parameters that help in measuring the degree of oxidation, i.e., the level of chemical deterioration. It provides the maintenance. The last section discusses the process of flushing and how to use it. Flushing may often be required when the system is new or during subsequent service, particularly after repairs, if significant contamination has occurred. The various things one needs to do before flushing are outlined here.

This chapter discusses the different types of hydraulic media in detail. It begins by presenting a brief history of the hydraulic age. It began with the existence of water. Water was also utilized as the hydraulic medium in the famous subterranean power transmission network. Continuing efforts to achieve improved efficiency resulted in designs incorporating higher operating pressures, but also higher system temperatures. The inherent advantages of hydraulic equipment were quickly appreciated by the mining and metallurgical industries. Thus, the introduction of hydraulic units proceeded with increasing momentum. During recent years, an increasingly greater attention has been directed towards health and safety considerations and the need to conserve our environment. Among the most used hydraulic media today are oil-in-water emulsions, water–glycol solutions, mineral oils, esters, and certain other synthetic fluids. The chapter also discusses the ideal hydraulic medium and lists the properties that are required for any hydraulic medium to be ideal. Finally, it concludes that mineral off-based media are predominantly the most common hydraulic fluids in use today. The mineral off-based media reflects a superior combination of advantageous properties with respect to compressibility, vapor pressure, lubricating properties, corrosion protection, chemical stability, and price.

Publisher Summary This chapter discusses the hydraulic brake fluids and the developments done in the hydraulic brake systems. Since the introduction of hydraulic brake systems, on-going research has resulted in improved brake-fluid quality to keep pace with automotive developments. The essential function of a brake system is to convert kinetic energy of the moving vehicle into heat. The braking systems of modern vehicles are subject to increasingly high temperatures, and the brake fluids must possess adequate thermal stability and low vapor pressure. Also, it must display suitable flow properties over the entire range of anticipated operational temperatures. Brake fluid should protect all metal components against corrosion and be fully compatible with seals and elastomers. The chapter also discusses other types of brakes such as silicone brake fluids, hydrocarbon brakes, mineral-oil brakes, and oil-immersed (wet) brakes in comparison to the hydraulic brakes.

This chapter explores the fire-resistant fluids. It begins by listing some of the most common types of fire-resistant mediums. Although these products present a significantly lower fire hazard than conventional mineral oil-based fluids, the individual fire-resistant products often possess certain other less advantageous properties. The chapter provides various examples of these properties. And the properties of various fire-resistant fluids are compared in a table format. Another section of the chapter is dedicated to the description of conversion of exiting systems to fire-resistant fluids. Unless specifically designed for a particular fire-resistant medium, most hydraulic equipment is normally designed for the use of mineral hydraulic oils. Successful conversion to fire-resistant fluids is dependent upon the careful selection of fluid types suitable for the system components and operational parameters. It outlines various suggested guidelines to convert the existing systems. Moreover, it discusses the maintenance of fire-resistant fluids. These require greater vigilance with respect to fluid maintenance than is normal for conventional mineral hydraulic fluids. Finally, the chapter concludes that once a correct combination of system design and hydraulic fluid is established, the key to economic and effective operation is strict adherence to certain things. These are manufacturers' recommendations, systematic inspection of filters, and periodical monitoring of the hydraulic fluid by laboratory examination.

This chapter discusses the role of hydraulic fluids in affecting/harming the environment. Recently, vigilance has increased towards the serious threats to humanity posed by industrial activities and associated pollution of the environment. And hydraulic fluids find a special place under this vigilance, as they are utilized in relatively large volumes for various equipments for outdoor operations. First of all, there is the danger of leakage. Also, the sudden rupture of a flexible hydraulic hose may result in considerable pollution of the surroundings and ground water. The chapter also discusses biodegradability and the tests to determine biodegradability. The discussion here emphasizes the fact that hydraulic fluids are often used along with additives. Thus, it becomes even more complicated because most of these additives are often slowly biodegraded. So, even biodegradable base oil would be under question due to the fact that the additives are almost always present. Finally, it describes the biodegradable hydraulic media and presents a comparison of the properties of various typical biodegradable fluids with those of a conventional mineral hydraulic oil.

This chapter presents a detailed analysis of the used hydraulic oil. The condition of a hydraulic fluid is normally monitored by various aspects. These are periodical determination of viscosity, total acidity, water content, and visual inspection with respect to mechanical impurities. On the basis of these results, it can be decided whether the oil is suitable for further use. These results can be further supplemented by various tests for a complete assessment. These supplementary tests are spectral analysis, particle counts, ferrography, infrared absorption analysis, and oxidation tests. Further, it provides the interpretation of these test results. And emphasizes that determination of the wear metals present in a used oil sample may yield valuable information with respect to the wear pattern of a particular system under the actual conditions of operation. The last section of the chapter discusses the condition monitoring and oil change as a cost-effective method. It is hardly remunerative to perform regular laboratory analyses on small systems and oil change intervals are decided on the basis of experience. Large hydraulic systems, however, often contain several tons of hydraulic fluid. And the condition of the oil charge is normally checked by regular analyses.

Publisher Summary This chapter explores the future perspectives of hydraulic fluids. Further developments are anticipated in the direction of high-quality multi-functional fluids, permitting increased rationalization and cost savings. New, unconventional components with unique properties are expected to be introduced as industrial technological innovation progresses. Also, research directed towards improved fire-resistant hydraulic fluids for aviation, aerospace and military applications continues. In order to satisfy the most extreme performance requirements, only fluorinated compounds appear suitable at present; this seems in conflict with environmental considerations, e.g., biodegradability. Moreover, the increasing use of sub-sea modules in offshore oil production has intensified the search for environmentally safe control systems. Finally, the chapter concludes that environmental considerations will undoubtedly receive high priority in the future development of hydraulic systems and associated functional fluids. A whole new generation of “environmentally friendly” hydraulic fluids is expected to appear on the market during the next few years, together with a corresponding range of specialized equipment from the component manufacturers, tailored to the requirements of the new media.

This chapter discusses the various test methods organized especially to check and rate hydraulic media. It begins by listing the name of the organizations that issue the majority of standardized test methods. Besides these organizations, there are many “in-house” procedures developed by pump manufacturers, oil companies, etc. This is followed by a detailed description of the several physical and chemical properties that are used as a basis to test hydraulic media. These are kinematic viscosity, pour point, flash point, neutralization number, foaming properties, air release, oxidation stability, thermal stability, among others. Further, the chapter discusses the numerous mechanical properties that are used to test hydraulic media. There are just two mechanical properties that are considered for such a test. These are anti-wear properties and shear stability.

Publisher Summary This chapter discusses the process of selecting a suitable hydraulic fluid. To ensure a reliable choice of suitable hydraulic fluid, it is essential to start by compiling information as detailed as possible concerning the actual system and operating conditions. It lists the factors that need to be followed to find a suitable hydraulic fluid. If necessary, the final selection of a hydraulic fluid should be made after also considering possible modification of the system. It should be able to accommodate a preferred fluid type, for technical, economic or rationalization reasons. Finally, the chapter concludes by presenting situations when one needs to use synthetic or mineral fluids. And it emphasizes that particular attention must be directed towards compatibility with surface coatings, seals and other eventual elastomeric materials when selecting a synthetic fluid.

Publisher Summary This chapter discusses the health and safety hazards related to hydraulic fluids. Much effort is expended to ensure safe working conditions and establish a favorable environment. However, it is unfortunately a sober fact that no product is completely safe in all respects, and strict adherence to adequate safety precautions should be emphasized. Hydraulic fluids have the advantage of being used in enclosed systems. It is therefore mainly during filling, due to leakages, or during maintenance work, that the possibility of physical contact with the hydraulic medium arises. Hydraulic fluids represent a relatively insignificant health hazard, provided safety precautions in accordance with the relevant Materials Safety Data Sheet (MSDS) are followed during maintenance work. The chapter summarizes the possible health hazards that can be caused because of physical contact with hydraulic fluids. And finally, it concludes that companies should assemble a product register, including a MSDS for every product utilized, stored or transported by the company. These data sheets should provide all necessary information concerning health hazards, handling precautions, labeling, first-aid, waste disposal, etc.

This chapter discusses the uses of hydraulic fluids for military and aerospace applications. Military and aerospace applications utilize a broad spectrum of hydraulic fluids, ranging from simple straight mineral oils to highly specialized synthetic fluids. This area of application is dominated by a high degree of interest in fire-resistant media with widespan temperature capabilities. The chapter presents a list of a selection of the most well-known military specifications. The chapter is divided into three sections. The first one discusses the aircraft and aerospace. The second one deals with combat vehicles and artillery and the third one covers the naval vessels. Significant advances within the aerospace industry have been accompanied by correspondingly demands on hydraulic fluids required to operate in these systems. Manual controls have been replaced by hydraulics and the number of hydraulically operated functions has increased rapidly, as has the complexity of the circuits. Earlier hydraulic fluids utilized by NATO forces were almost exclusively mineral oil products for vehicles and artillery. However, the research was intensified on fire-resistant media. This resulted in a developed and corrosion-inhibited version of the synthetic hydrocarbon. And hydraulic fluids used in naval vessels are at present mainly based on conventional mineral oil fluids.