Boiler glossary

Boiler glossary O


OEM -- Original Equipment Manufacturer. Confusingly manufacturers who resell another company's product under their own name and offering its own support and warranty.
OHM -- The SI unit of electrical resistance, such that 1 ampere through it produces a potential difference across it of 1 volt. Symbol
OMNIBUS-BAR -- The original term from which the commonly used expression bus-bar is derived.
ONCE-THROUGH BOILER -- A monotube boiler in which the feed water evaporates to steam immediately in the tube. Also referred to as Flash Boiler.
OPPOSED-CYLINDER ENGINE -- An engine with cylinders, or banks of cylinders, on opposite sides of the crankcase in the same plane, their connection-rods working on a common crankshaft placed between them.
ORIFICE -- The opening from the whirling chamber of a mechanical atomizer or the mixing chamber of a steam atomizer through which the liquid fuel is discharged.
ORIFICE GAUGE -- A flow gauge consisting of a thin orifice plate clamped between pipe flanges, with pressure take-offs drilled into the adjacent pipes, or of a thick orifice plate similarly, clamped but containing its own pressure take-offs.
OSMOSIS -- Diffusion of a solvent through a semipermeable membrane into a more concentrated solution, tending to equalize the concentrations on both sides of the membrane.
OSMOTIC PRESSURE -- The pressure exerted by a dissolved substance in virtue of the motion of its molecules. It may be measured by the pressure that must be applied to a solution in order just to prevent osmosis into the solution.
OUTSIDE LAP -- The amount by which the slide-valve of a reciprocating steam-engine overlaps the edge of the steam ports when in mid-position. Also called Steam lap.
OZONE -- O3  A bluish, toxic gas produced by the action of ultraviolet radiation or electric corona discharge on oxygen or air. Powerful oxidizing agent.