Ultrasonic cleaning: sends high-pitched sound waves through a liquid solvent
to remove dirt, grease and small metal particles quickly and effectively from
small corners and crevices.
Unloading valve (hydraulics): a device that directs hydraulic fluid back to the
reservoir at low pressure when there is no demand on the system.
Unworked pen/penetration: (ASTM D-217) the penetration at 77°F of a sample
of grease that has experienced minimum handling in transfer to the test
apparatus and that has not been subjected to the action of a grease worker.