Page 42 - PNEUMATIC AND HYDRAULIC

iv. Oxidation and thermal stability - Over time, fluids oxidize and form acids,

sludge, and varnish. Acids can attack system parts, particularly soft metals.
Extended high-temperature operation and thermal cycling also encourage the

formation of fluid decomposition products.

v. Seal compatibility - In most systems, seals are selected so that when they

encounter the fluid they will not change size or they will expand only slightly,
thus ensuring tight fits. The fluid selected should be checked to be sure that

the fluid and seal materials are compatible, so the fluid will not interfere with
proper seal operation.

vi. Fluid life, disposability - There are two other important considerations that do

not directly relate to fluid performance in the hydraulic system, but have a

great influence on total cost. They are fluid life and disposability.

vii. Fire-resistant fluids- The overwhelming majority of hydraulic components

and systems are designed to use oil-based hydraulic fluids. No wonder; these
fluids rarely present significant operating, safety, or maintenance problems.

Unfortunately, there are circumstances where using oil-based fluid should be

avoided. One common fluid power application is in an environment with
potential ignition sources - an open flame, sparks, or hot metal. In these

environments, a leak spraying from a high-pressure hydraulic system could
cause a serious fire and result in major property damage, personnel injury, or

even death.

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