Boiler glossary

Boiler glossary U

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UL -- The Underwriters' Laboratories, Inc.
U-LEATHER -- A flexible ring of U-section, used to pack the glands of fluid power pistons or rams. The open side is the pressure side, and the fluid is expanding the inner face against the ram, effectively seals it against leakage. Also called U-PACKING.
ULLAGE -- The gas volume in an oil tank.
ULLAGE GAUGE -- The distance from the liquid surface to the top of the tank.
ULTRASONIC CLEANING -- A cleaning process effective for small crevices, blind holes, fine screw threads, etc., in which the part is immersed in water or solvent vibrating at ultrasonic frequency.
ULTRASONIC TESTING -- A method of testing in which an ultrasonic source is pressed against the part to be tested and the vibrations are reflected from a discontinuity or another surface of the part, to generate a signal in the receiver. The time lag of the echo is measured to determine the distance to the discontinuity or the work-piece thickness.
UNIFLOW ENGINE -- A steam-engine in which the steam enters through drop valves at the end of the cylinder and exhausts through a piston-controlled belt of ports at the centre of the cylinder.
UNDERFEED STOKER-- A mechanical stoker in which the fuel is fed automatically and progressively from below the fire, and gradually forced up into the active zone, air being injected into the fuel bed just below the combustion-level.
UNIT HEATER -- A heating device, usually located directly in the space to be heated, consisting of a fan and a heat source.
UNIT WEIGHT -- In a steam boiler, the ratio of the mass of the complete boiler to that of the hourly maximum steam production.
U-PACKING -- See U-LEATHER.
UPTAKE -- The duct that leads the flue gases of a marine boiler to the base of the funnel.
USEFUL THERMAL OUTPUT-- The thermal energy made available for use in any industrial or commercial process, or used in any heating or cooling application, i.e., total thermal energy made available for processes and applications other than electrical generation.