ULTIMATE STRENGTH - The maximum stress (tensile, compressive or shear) a material can sustain without fracture. It is determined by dividing maximum load by the original cross-sectional area of the specimen.

ULTRA FILTRATION - A process that forces water through a filtering membrane by means of pressure gradients in order to obtain ultra pure water.

UNDER DEPOSIT ATTACK - Corrosion under or around a localized deposit on a metal surface (a form of crevice corrosion).

UNITARY SYSTEM - A room unit which performs part or all of the air conditioning functions. It may or may not be used with a central fan system.

UNLOADER - A device in or on the compressor for equalizing high-side and low-side pressures for a brief time during starting and for controlling compressor capacity by rendering one or more cylinders ineffective.

UP FLOW - The operation of an ion-exchange unit in which solutions are passed in at the bottom and out at the top of the container.

UP FLOW FILTER - A unit containing a single filter medium, usually with graded sand.

UP FLOW FURNACE - A furnace in which the heated air flows upward as it leaves the furnace.

UPSTREAM - The inlet side of an instrument, a pump, valve, etc..

UTILITY TRANSFORMER - Primary and secondary coils of wire which reduce (step down) the utility supply volt age for use within a facility.

U-TUBE MANOMETER - A U-shaped section of plastic or glass tubing that is partially filled with water or mercury. They are used to measure the lower pressure ranges of gases.