A membrane based filtration system in which the pore sizes range from 0.002 to 0.1 microns.
ULTRAVIOLET (UV) LIGHT
Radiation (light) having a wavelength shorter than 3900 angstroms, the wavelength of visible light and longer than 100 angstroms, the wavelengths of x-rays. This wavelength puts ultraviolet light at the invisible violet end of the light spectrum. UV light is used as a disinfectant. Water treated by ultraviolet light should be free from particulate materials or turbidity so as to prevent micro-organisms from being shielded from the incident UV radiation.
UNDERDRAIN
The distribution system at the bottom of the filter which collects the water uniformly during the filter cycle, and which distributes the backwash water uniformly during the cleaning operation. Normally applies to sand filters.
UNDERWATER LIGHTS
A light designed to illuminate a pool from beneath the water surface.
UNIVERSAL GRAVITATION CONSTANT
The acceleration of a free falling body in the gravity field of the Earth. g = 32.2 feet/second/second
UPPER DISTRIBUTION SYSTEM
Those devices designed to distribute the water entering a permanent medium filter in a manner so as to prevent movement or migration of the filter medium. This system shall also properly collect water during filter backwashing unless other means are provided.