Ultra-fine wire cloth. A group of industrial wire cloth specifications with lighter than normal wire. The wire diameter of this grade produces the highest percentage of open area of all other grades for any specific mesh size. This cloth is used in multiple layer screens. See: market grade cloth, mill grade cloth, tensile bolting cloth, and calendered.
Ultraviolet light. Light waves shorter than the visible blue and violet waves of the spectrum. Crude oil, colored distillates, residium, a few drilling-fluid additives, and certain minerals and chemicals fluorescein the presence of ultraviolet light. These substances, when present in drilling fluid, may cause the drilling fluid to fluoresce.
Unbalanced elliptical motion. An elliptical motion of a shale shaker screen such that the ellipse axes at the feed end are tilted toward the discharge end of the screen and the ellipse axes at the discharge end are tilted toward the feed end. Usually these screens are tilted downward to assist solids removal from the end of the screen. The vibrator is usually located above the center of gravity of the shaker basket.
Underflow. (1) Centrifugal separators: the discharge stream from centrifugal separators that contains a higher percentage of solids than does the feed. (2) Screen separators: the discharge stream from screen separators that contains a lower percentage of solids than does the feed.
Underflow header. A pipe, tube, or conduit into which two or more hydrocyclones discharge their underflow.
Underflow opening. See: apex, apex valve.
Undersize solids particles. (1) Particles, in a given situation, that will pass through the mesh of the screen in use. (2) Particles, in a given situation, that will remain with the liquid phase when subjected to centrifugal force.
Underslung. Field terminology denoting that the support ribs for the shaker screen are located above the screen surface. See: overslung.