ULTIMATE ANALYSIS – See “Analysis Ultimate.“
UL LISTED – Product certification that indicates the product meets safety standards determined by Underwriters Laboratories. (ULC and cUL indicate Canadian requirements.)
UNACCOUNTED-FOR LOSS – That portion of a boiler heat balance which represents the difference between 100 per cent and the sum of the heat absorbed by the unit and all the classified losses expressed as per cent.
UNBURNED COMBUSTIBLE – The combustible portion of the fuel which is not completely oxidized.
UNFIRED PRESSURE VESSEL – A vessel designed to withstand internal
pressure, neither subjected to heat from products of combustion nor an integral part of a fired pressure vessel system.
USE FACTOR – The ratio of hours in operation to the total hours in that period.
VA – Volt amperes.
VAPOR – The gaseous product of evaporation.
VAPORIZATION – The change from liquid or solid phase to the vapor phase.
VELOCITY PRESSURE – The measure of the kinetic energy of a fluid.
VENT – An opening in a vessel or other enclosed space for the removal of gas or vapor.
VERTICAL FIRING – An arrangement of a burner such that air and fuel are discharged into the furnace in practically a vertical direction.
VISCOSITY – Measure of the internal friction of a fluid or its resistance to flow.
VOLATILE MATTER Those products given off by a material as gas or vapor, determined by definite prescribed methods.
VOLUME OF AIR – The number of cu ft of air per min expressed at fan outlet conditions.
WASTE HEAT – Sensible heat in non-combustible gases discharged to the environment.
WATER – A liquid composed of two parts of hydrogen and sixteen parts oxygen by weight.
WATER COLUMN – A vertical tubular member connected at its top and bottom to the steam and water space respectively of a boiler, to which the water gauge, water level controls, and fuel cutoff may be connected.
WATER GAUGE – The gauge glass and its fittings for attachment.
WATER HAMMER – A sudden increase in pressure of water due to an instantaneous conversion of momentum to pressure.
WATER LEVEL – The elevation of the surface of the water in a boiler.
WATER SOFTENER – Removes hardness (CaCO3) from water through an ion exchange of sodium with calcium and magnesium.
WATER TUBE – A tube in a boiler having the water and steam on the inside and heat applied to the outside.
WATER VAPOR – A synonym for steam, usually used to denote steam of low absolute pressure.
WEEP – A term usually applied to a minute leak in a boiler joint which forms droplets (or tears) of water very slowly.
WETBACK BOILER – Firetube boiler design wherein the back portion of the boiler has a water jacket.
WET–BULB TEMPERATURE – The lowest temperature which a water wetted body will attain when exposed to an air current. This is the temperature of adiabatic saturation, and can be used to measure humidity.
WETNESS – A term used to designate the percentage of water in steam. Also used to describe the presence of a water film on heating surface interiors.
WET STEAM – Steam containing moisture.
WINDBOX – A chamber below the grate or surrounding a burner, through which air under pressure is supplied for combustion of the fuel.
WINDBOX PRESSURE – The static pressure in the windbox of a burner or stoker.