Rust Protection

Dissolved water in a phosphate ester hydraulic fluid does not
cause rust, although the separated water phase can cause
rapid corrosion of ferrous parts. Water in normal concentrations
of up to about 1% is soluble in the fluid and not a cause for
rust-related concerns. However, in absence of potent rust
inhibitors in the fluid, if water concentration exceeds 3%,
equipment damage can be rapid and severe.

As the photos to the right demonstrate, HyJet IV-Aplus offers
superior rust protection relative to competitive Type IV products
in the ASTM D665A rust test. This superior rust protection
provides a measure of security against potentially damaging
water contamination of an aircraft hydraulic system.

• HyJet IV-Aplus shows no rust on the test parts at
5% or 10% water mixed with fluid. The standard ASTM
D665A test measures rust at 10% water.

• Competitive Type IV fluids show severe rust even at
5% water. At 10% water the rust damage observed
becomes extremely severe.