Description / Abstract:
Although there is controversy regarding the chemical form of
chlorine and its relation to harmful effects in the hydraulic fluid
(i.e., chloride ions versus organic chloro-compounds versus total
chlorine in all forms), it is generally agreed that total chlorine
content should be measured and controlled. In the near future, the
ban on the manufacture of chlorinated solvents, out of concern for
depletion of the ozone layer, may in itself diminish or eliminate
chlorine contamination related aircraft malfunctions. It is
generally accepted that hydraulic fluid contamination should be
held to a minimum under all conditions. The benefits of low
contamination levels are improved performance, lower maintenance
due to lower wear, corrosion and erosion, longer fluid life, longer
component life, etc.
Contaminants can be classified into two general types: those
that are insoluble and those that are soluble in the hydraulic
fluid. The insoluble solid type is most common and is usually
referred to as particulate matter. Its measurement and removal have
been the subject of much investigation and standardization which is
well documented in technical literature. The insoluble liquid type
contaminant is much less common. The resulting two phase system is
often observed as hazy or cloudy fluid appearance and the
recommended action is to remove the contaminated hydraulic fluid
from the system.
Soluble type contaminants are more difficult to detect and to
determine quantitatively. They can easily escape notice,
particularly when present in small amounts. Gross contamination
usually results in significant changes in fluid physical properties
and can be determined by such changes. Smaller amounts are
difficult to detect and measure and usually require sophisticated
analytical techniques - such as infrared and other spectral
techniques, gas chromatography (both head space and electron
capture), microcoulometry, x-ray fluorescence, etc.
Generally, the presence of undesirable soluble contaminants is
unknown until they have been shown to cause performance problems.
Hydraulic fluid formulations contain soluble additives in base
stocks giving beneficial effects on performance. The range of
possible undesirable soluble contaminants can encompass innumerable
materials - solids, liquids or gases.
Purpose:
Of all the potential soluble contaminants, this SAE Aerospace
Information Report (AIR) covers only chlorine containing materials,
their detection, their effects, and suggests ways to prevent their
contaminating aircraft hydraulic fluids. This document will limit
itself to "chlorine containing compounds" in MIL-H-5606 and
MIL-H-83282 fluids. The presence and effects of other types of
materials will not be discussed in this document.