'Foreign Contaminates' - Hydraulic RAM Fluid Contamination

TYPES OF CONTAMINATION THAT MAY BE PRESENT IN HYDRAULIC RAM's

There are many different forms of contamination, including liquids, gasses, and solid matter of various composition, size, and shape. Normally, contamination in an operating hydraulic system originates at several different sources.

Effects of contamination may include:


Following testing, Hydraulic RAM Repairs UK Ltd has determined the rate of its introduction depends upon many factors directly related to wear and chemical reaction. Contamination removal can reverse this trend. Production of contaminants in the hydraulic system increases with the number of system components. The rate of contamination from external sources is not readily predictable. A hydraulic system can be seriously contaminated by poor maintenance practices that lead to introducing large amounts of external contaminants. Poorly maintained SE is another source of contamination. Contaminants in hydraulic fluids are classified as particulate and fluid contamination. Other studies carried out by Hydraulic RAM Repairs UK Ltd revealed they may be further classified according to their type, such as organic, metallic solids, nonmetallic solids, foreign fluids, air, and water.

PARTICULATE CONTAMINATION

The type of contamination most often found in aircraft hydraulic systems consists of solid matter. This type of contamination is known as particulate contamination. The size of particulate matter in hydraulic fluid is measured in microns (millionths of a meter). The largest dimensions (points on the outside of the particle) of the particle are measured when determining its size. Contamination of hydraulic fluid with particulate matter is a principal cause of wear in hydraulic pumps, actuators, valves, and servo valves. Spool-type electro hydraulic valves have been used in particle contamination experiments. The valves are easy to control and respond rapidly to repositioning. In these experiments, the valves were operated with both ultra clean and contaminated hydraulic fluids. The experiments proved that wear is accelerated by even small amounts of contamination. Contamination increases the rate of erosion of the sharp spool edges and general deterioration of the spool surfaces. Because of the extremely close fit of spools in servo valve housings, the valves are particularly susceptible to damage or erratic operation when operated with contaminated hydraulic fluid. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Organic Contamination

Organic solids or semisolids are one of the particulate contaminants found in hydraulic systems. They are produced by wear, oxidation, or polymerization (a chemical reaction). Organic solid contaminants found in the systems include minute particles of O-rings, seals, gaskets, and hoses. These contaminates are produced by wear or chemical reaction. Oxidation of hydraulic fluids increases with pressure and temperature. Antioxidants are blended into hydraulic fluids to minimize such oxidation. Oxidation products appear as organic acids, asphaltics, gums, and varnishes. These products combine with particles in the hydraulic fluid to form sludge. Some oxidation products are oil soluble and cause an increase in hydraulic fluid viscosity, while other oxidation products are not oil soluble and form sediment. Oil oxidation products are not abrasive. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

These products cause system degradation because the sludge or varnish like materials collect at close-fitting, moving parts, such as the spool and sleeve on servo valves. Collection of oxidation products at these points causes sluggish valve response. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Metallic Solid Contamination

Metallic solid contaminants are usually found in hydraulics systems. The size of the contaminants will range from microscopic particles to those you can see with the naked eye. These particles are the result of the wearing and scoring of bare metal parts and plating materials, such as silver and chromium. Wear products and other foreign metal particles, such as steel, aluminum, and copper, act as metallic catalysts in the formation of oxidation products. Fine metallic particles enter hydraulic fluid from within the system. Although most of the metals used for parts fabrication and plating are found in hydraulic fluid, the major metallic materials found are ferrous, aluminum, and chromium particles. Hydraulic pumps usually contribute the most contamination to the system because of their high-speed, internal movement. Other hydraulic systems produce hydraulic fluid contamination due to body wear and chipping. Hydraulic actuators and valves are affected by contamination. Large metallic or hard nonmetallic particles collect at the seal areas. These particles may groove the inside wall of the actuator body due to a scraping action. Smaller particles act as abrasives between the seals and the actuator body, causing wear and scoring. Eventually, the fluid leaks and the seals fail because the seal extrudes into the enlarged gap between the piston head and the bore of the actuator body. Once wear begins, it increases at a faster rate because wear particles add to the abrasive material. In a similar manner, metallic or nonmetallic parts may lodge in the poppets and poppet-seat portions of valves and cause system malfunction by holding valves open. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Inorganic Solid Contamination

The inorganic solid contaminant group includes dust, paint particles, dirt, and silicates. These and other materials are often drawn into hydraulic systems from external sources. The wet piston shaft of a hydraulic actuator may draw some of these foreign materials into the cylinder past the wiper and dynamic seals.The contaminant materials are then dispersed in the hydraulic fluid. Also, contaminants may enter the hydraulic fluid during maintenance when tubing, hoses, fittings, and components are disconnected or replaced. To avoid these problems, all exposed fluid ports should be sealed with approved protective closures. Glass particles from glass bead peening and blasting are another contaminant. Glass particles are particularly undesirable because glass abrades synthetic rubber seals and the very fine surfaces of critical moving parts.

FLUID CONTAMINATION

Hydraulic RAM fluid can be contaminated by air, water, solvents, and foreign fluids. These contaminants and their effects are detailed in the following as prepared by Hydraulic RAM Repairs UK Ltd.

Air Contamination

Hydraulic fluids are adversely affected by dissolved, entrained, or free air. Air may be introduced through improper maintenance or as a result of system design. Air is sometimes introduced when changing filters. You can minimize this kind of contamination by putting hydraulic fluid into the filter holder before reassembling the filter. By doing this, you have introduced less air into the hydraulic system. The presence of air in a hydraulic system causes spongy response during system operation. Air causes cavitation and erodes hydraulic components. Air also contributes to the corrosion of hydraulic components. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Water Contamination

Water is a serious contaminant of hydraulic systems. Corrective maintenance actions must be taken to remove ail free or emulsified water from hydraulic systems. Hydraulic ram fluids and hydraulic system components are adversely affected by dissolved, emulsified, or free water. Water may be induced through the failure of a component, seal, line or fitting, poor or improper maintenance practices, and servicing. Water may also be condensed from air entering vented systems. The presence of water in hydraulic systems can result in the formation of undesired oxidation products, and corrosion of metallic surfaces will occur. These oxidation products will also cause hydraulic seals to deteriorate and fail, resulting in leaks. If the water in the system results in the the operation of valves, actuators, or other moving parts within the system. This is particularly true of water located in static circuits or system extremities and subject to high-altitude, low-temperature conditions. Microorganisms will grow and spread in hydraulic fluid contaminated with water. These microorganisms will clog filters and reduce system performance. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Solvent Contamination

Solvent contamination is a special form of foreign- fluid contamination. The original contaminating substance is a chlorinated solvent introduced by improper maintenance practices. It is extremely difficult to stop this kind of contamination once it occurs. This type of contamination can be prevented by using the right cleaning agents when performing hydraulic system maintenance. Chlorinated solvents, when allowed to combine with minute amounts of water, hydrolyze to form hydrochloric acids. These acids attack internal metallic surfaces in the system, particularly those that are ferrous, and produce a severe rust like corrosion that is virtually impossible to arrest. Extensive component overhaul and system decontamination are generally required to restore the system to an operational status. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd

Foreign Fluids Contamination

Contamination of hydraulic fluid occurs when the wrong fluids get into the system, such as oil, engine fuel, or incorrect hydraulic fluids. Hydraulic oil ceders, which are used in some aircraft, leak and cause contamination of hydraulic fluids. If you think that contamination has occurred, the system must be checked by chemically analyzing fluid samples. This analysis is conducted by the cognizant engineering activity, which verifies and identifies the contaminant and directs decontamination procedures. The effects of foreign fluid contamination depend upon the nature of the contaminant. The compatibility of the construction materials and the system hydraulic fluid with the foreign fluid must be considered when dealing with contamination. Other effects of this type of contamination are hydraulic fluid reaction with water and changes in flammability and viscosity characteristics. The effects of contamination may be mild or severe, depending upon the contaminant, how much is in the system, and how long it has been in the system. Further information on this subject is available from Hydraulic RAM Repairs UK Ltd