Hydraulic fluids contamination

Hydraulic fluid contamination may be described as any foreign material or substance whose presence in the fluid is capable of adversely affecting system performance or reliability. It may assume many different forms, including liquids, gases, and solid matter of various composition, sizes, and shapes. Solid matter is the type most often found in hydraulic systems and is generally referred to as particulate contamination. Contamination is always present to some degree, even in new, unused fluid, but must be kept below a level that will adversely affect system operation. Hydraulic contamination control consists of requirements, techniques, and practices necessary to minimize and control fluid contamination. 

Hydraulic fluid contaminants have been identified in at least 10 of 1,428 current or former NPL Sites (HazDat 1996). All of these sites are located in the conterminous United States. The frequency of these sites can be seen in Figure 5-1. However, the number of sites evaluated for hydraulic fluids is not known. 

Selection and care of the hydraulic fluid for a machine will have an important effect on how it performs and on the life of the hydraulic components. During the design of equipment that requires fluid power, many factors are considered in selecting the type of system to be used-hydraulic, pneumatic, or a combination of the two. Some of the factors required are speed and accuracy of operation, surrounding atmospheric conditions, economic conditions, availability of replacement fluid, required pressure level, operating temperature range, contamination possibilities, cost of transmission lines, limitations of the equipment, lubricity, safety to the operators, and expected service life of the equipment. 

After the type of system has been selected, many of these same factors must be considered in selecting the fluid for the system. This chapter is devoted to hydraulic fluids. Included in it are sections on the properties and characteristics desired of hydraulic fluids types of hydraulic fluids hazards and safety precautions for working with, handling, and disposing of hydraulic liquids types and control of contamination and sampling. 

Cleanliness in hydraulic systems has received considerable attention recently. Some hydraulic systems, such as aerospace hydraulic systems, are extremely sensitive to contamination. Fluid cleanliness is of primary importance because contaminants can cause component malfunction, prevent proper valve seating, cause wear in components, and may increase the response time of servo valves. Fluid contaminants are discussed later in this chapter. 

Water Water is a serious contaminant of hydraulic systems. Hydraulic fluids are adversely affected by dissolved, emulsified, or free water. Water contamination may result in the formation of ice, which impedes the operation of valves, actuators, and other moving parts. Water can also cause the formation of oxidation products and corrosion of metallic surfaces. 

Solvents Solvent contamination is a special form of foreign fluid contamination in which the original contaminating substance is a chlorinated solvent. Chlorinated solvents or their residues may, when introduced into a hydraulic system, react with any water present to form highly corrosive acids. 

Maintaining hydraulic fluid within allowable contamination limits for both water and particulate matter is cmcial to the care and protection of hydraulic equipment. Filters will provide adequate control of the particular contamination problem during all normal hydraulic system operations if the filtration system is installed properly and filter maintenance is performed properly. Filter maintenance includes changing elements at proper intervals. 

Clean hydraulic fluid is essential for proper operation and acceptable component life in all hydraulic systems. While every effort must be made to prevent contaminants from entering the system, contaminants that do find their way into the system must be removed. Filtration devices are installed at key points in fluid power systems to remove the contaminants that enter the system along with those that are generated during normal operations of the system. 

Frequency of NPL Sites with Hydraulic Fluid and Hydraulic Fluid Component Contamination... 

Data suggestive of adverse reproductive effects after an assumed acute oral exposure to organophosphate ester hydraulic fluids are restricted to an observation of reduced lactation and delayed estrus with no coincident gross lesions in cows that ingested grass contaminated with Fyrquel 150 (Beck et al. 1977). 

After a single dermal exposure to waste from the reclamation of a Fyrquel hydraulic fluid that may have been contaminated with tri-or/7 o-cresyl phosphate (TOCP), no apparent signs of neurotoxicity were observed in calves of 10 cows that manifested neurotoxicity just after the birth of the calves. The cows were apparently also exposed orally concurrent to the dermal exposure (Julian et al. 1976). No intermediate- or chronic-duration dermal studies examining developmental effects in animals were located. 

In severe cases, paralysis may also affect the upper limbs. Recovery is usually slow and is not always complete. Tri-ort/20-cresyl phosphate (TOCP), an isomer found in tricresyl phosphate, was the first organophosphate ester linked to OPIDN, being responsible for an epidemic of paralysis in the southeastern United States that led to the name "ginger jake paralysis" (Smith 1930) (see Section 2.4). Current manufacturing processes for organophosphate ester hydraulic fluids are designed to minimize production of this isomer, although it is possible that fluids disposed of in the past may be contaminated. 

An organophosphate ester commonly used in hydraulic fluids, tricresyl phosphate (TCP), and tri-ortho-cresyl phosphate (TOCP), a possible contaminant of older formulations of TCP, have been shown to alter testicular morphology, testicular function, and reproductive function in rodents after oral exposure (Carlton et al. 1987 Chapin et al. 1988 NTP 1994 Somkuti et al. 1987a, 1987b). 

There is no available information on absorption of mineral oil hydraulic fluids following inhalation or dermal absorption. There are data suggesting that mineral oil aerosols are cleared from the lungs via alveolar macrophages. No specific methods to reduce absorption of dermally applied or inhaled mineral oil hydraulic fluids were located, but it is expected that removal of contaminated clothing and multiple washings of contaminated skin would reduce the dermal absorption of these materials. 

In the past, hydraulic fluids using mineral oils sometimes included such additives as PCBs to improve the thermal resistance or other properties of the resulting fluids. While such uses of PCBs have been discontinued, PCBs at NPL sites may be encountered as a component where hydraulic fluids are a site contaminant (ATSDR 1993b). 

One of the main human health concerns about organophosphate esters is the potential for neurotoxicity reactions, in particular a condition known as organophosphate-induced delayed neurotoxicity (OPIDN). Tri-ort/20-cresyl phosphate (TOCP) has been identified as one of the more potent OPIDN neurotoxins in humans, and was formerly a constituent in some organophosphate ester hydraulic fluid products (Marino 1992 Marino and Placek 1994). Production processes now routinely remove virtually all the TOCP. For instance, tricresyl phosphate (TCP) products now typically are manufactured to contain over 98% meta and para isomers and virtually no TOCP (Marino and Placek 1994). Products containing these compounds associated with OPIDN have now entirely disappeared from commercial use, and the vast majority of the industrial organophosphate esters are based on triaryl phosphates with no halogenated components (Marino 1992). At waste disposal sites, however, site contaminants from older product formulations containing the ortho form may be encountered. 

Before the 1960s, products were introduced based on alkyl aryl phosphates that could contain chlorinated aromatic hydrocarbons. Such products have now entirely disappeared from commercial use, and the vast majority of the industrial organophosphate esters are based on triaryl phosphates with no halogenated components (Marino 1992). However, at older waste disposal sites, hydraulic fluid site contaminants could contain chlorinated hydrocarbons. As with the PCBs formerly included as additives in other forms... 

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