Glossary of Terms Definition of Terms
ABRASIVE WEAR Wear caused by abrasive action of dirt and fine contaminants in the oil.
AERATION Presence of air bubbles in hydraulic oil...gives a foamy appearance.
CAVITATION Formation and collapse of vapor bubbles in hydraulic oil.
DIRT OR FINE CONTAMINANTS Very small particles of abrasive material suspended in hydraulic oil.  Usually not visible to the naked eye.
EROSION Removal of metal particles from the surface of a part, leaving a rough, pitted area.
FLUSHING Thorough cleaning of entire system to remove all contaminants that can or have caused pump failures.
GEAR TRACK Area in pump housing milled by gear teeth on initial pump break-in (at manufacture) to provide proper tip clearances.
HIGH OIL TEMPERATURE Temperature above 200 degrees (F), when the oil film weakens and its lubricating ability is reduced.
ISOLATION PLATE Support for pressure balance seals used to separate low pressure and high pressure areas of pressure balance system.
LACK OF OIL Low oil level in tank.  This can allow suction to be uncovered due to sloshing of oil.
METAL CONTAMINANTS Small particles of metal in the hydraulic oil.   Probably have worn from components in the system and may or may not be visible to the eye.
OVERPRESSURE Pressure in the system exceeds the specified relief valve pressure.
PRESSURE BALANCE Hydraulic loading of pressure plates to keep them firmly against gear ends.  This is essential for high pump efficiency.
PRESSURE PLATES Plates on each side of gears.  The pressure plates and housing form the pumping chamber.
TRAP Recess in the pressure plates that allow trapped fluid between the teeth of the pump gears to escape.

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