formation of ice, it will reduce fluid flow and impede 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. 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 rustlike corrosion that is virtually impossible to arrest. Extensive component overhaul and system decontamination are generally required to restore the system to an operational status. 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 com- patibility 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 con- tamination may be mild or severe, depending upon the contaminant, how much is in the system, and how long it has been in the system. SAMPLING POINTS Learning Objective:   Identify the procedures for sampling hydraulic fluid and the sampling point requirements. A fluid sampling point is a physical point in a hydraulic system from which small amounts of hydraulic fluid are drawn to analyze it for con- tamination. Sampling points include air bleed valves, reservoir drain valves, quick-disconnect fittings, removable line connections, and special valves installed for this specific purpose. Hydraulic fluid sampling points for most naval aircraft are designated in the applicable MIM. Two major factors determine if a sampling point is adequate—its mechanical feature and its location in the system. To determine the contamination level, a single fluid sample is required. This sample must be representative of the working fluid in the system, and it should be a “worst case” indication of the system particulate level. The worst case requirement is necessary because the particulate level in an operating system is not constant throughout the system. Instead, particulate levels differ because of the effects of components (such as filters) on circulating particulate. The mechanical features of a prospective sampling point are evaluated on the basis of accessibility and ease of operation. The sampling point should not distort the particulate level of the sampled fluid either by acting as a filter or by introducing external or self-generated contaminants. The latter point is particularly critical. You can minimize the introduction of external or self-generated contaminants before collecting a sample by cleaning the external parts of the valve or fitting and by dumping a small amount of the initial fluid flow. Consideration must also be given to removal of any static fluid normally entrapped between the actual sampling point and the main body of the fluid to be sampled. To do this, you dump an initial quantity of the sampled fluid. Problems may be encountered where a long line is involved, as in certain reservoir drain lines. You should take the fluid sample from a main system return line, pump suction line, or system reservoir. Also, take the sample upstream of any return or suction line filters that may be present. Do not take reservoir samples in a system that has a makeup reservoir, or if the reservoir is bypassed 4-7