CONTAMINATION The correct function of a hydraulic system is essential to the safe operation of an aircraft. Hydraulic fluid contamination may be described as any foreign material whose presence in the fluid is capable of adversely affecting the system performance or reliability.

It is essential that we maintain a level of cleanliness that ensures the system functions correctly. Hydraulic contamination control consists of those requirements, techniques, and practices, which minimize and control fluid contamination.

There are several sources of contamination that concern us with regards to hydraulics SOURCES OF CONTAMINATION

IN-BUILT In-built contamination is contamination introduced during the manufacturing process. Consisting mainly of dirt and metallic particles, a great deal of money and effort is spent to ensure that all traces are removed prior to entry into service. Rarely, components are received from manufacturers that do not meet the required standards

SYSTEM GENERATED System generated contamination is produced by the normal wear of components within the hydraulic system and also by chemical reactions within the hydraulic fluid..

The contamination consists mainly of metallic particles, the presence of which increases the system wear rate and the production of further contamination. This trend can be reversed by effective removal of contaminants at source, i.e. filtration

INTRODUCED Any contamination originating from an external source is termed 'introduced'. The most common cause of introduced contamination is poor trade practice during system maintenance.

ORGANIC Very fine contaminants within a fluid are normally organic in origin. Organic materials are formed as a result of the chemical breakdown of the fluid and seals within the system, usually as a result of the oxidization process.

Organic contamination consists of organic acids, gums, asphaltics, and varnishes. Contaminants in suspension may cause the fluid to take on a “smoky” appearance or may collect to form gums, sludge, and varnishes which can clog filters and close tolerance valves. Soluble contaminants can also affect the viscosity of the fluid.

METALLIC Metallic contamination is almost always present in hydraulic systems due to the normal wear and tear of system components.

Due to their continuous high-speed operation, pumps tend to be a major source of metallic contamination. Metallic contamination may also be introduced during system maintenance if appropriate prevention measures are not taken.

DIRT AND DUST Dirt and dust is primarily introduced into hydraulic systems during the course of maintenance. As such, it is also the easiest form of contamination to eliminate, simply by good husbandry. Additionally, dirt and dust may be drawn into the system past defective jack-ram wiper rings.

WATER Water can be introduced into hydraulic systems during maintenance, particularly during reservoir replenishment, where rainwater can collect on the fluid container. Condensation may also form in un-pressurized reservoirs leading to water contamination.

FOREIGN FLUIDS Foreign fluids introduced into a hydraulic system can cause catastrophic failure of system seals. The usual source of this contamination is the use of incorrect fluid during system maintenance