Boiler glossary

Boiler glossary D


DAMPER -- An adjustable iron plate or shutter fitted across a boiler flue to regulate the draught. Often provided with an automatic electro-mechanical device that closes the damper to prevent heat from escaping through the funnel during burner stop periods.
DEAERATOR -- A vessel in which boiler feed water is heated under reduced pressure in order to remove dissolved air.
DEAD ANGLE -- That period of a crank angle of a steam engine during which the engine will not start when the stop-valve is opened; due to the ports being closed by the slide-valve.
DEAD WEIGHT - The difference, in tons, between a ship's displacement at load draught and light draught. It comprises cargo, bunkers, stores, fresh water, etc.
DEHA -- Abbreviation for Diethylhydroxylamine, a clear colorless volatile liquid used in boiler systems as oxygen scavenger and it reacts with oxygen to form acetate, nitrogen and water.
DESIGN PRESSURE-- The pressure used in the design of a boiler for the purpose of calculating the minimum permissible thickness or physical characteristics of the different parts of the boiler.
DESUPERHEATER -- A device for removing all or part of the superheat from steam by spraying water into it or by use of a heat exchanger.
DISSOLVED SOLIDS -- Make-up water to a boiler usually contains minerals and impurities. These increase in concentration as water is boiled into steam. Dissolved solids are in true suspension and cannot be filtered out.
DIFFERENTIAL PRESSURE TRANSMITTER -- Mainly used for mass-flow-measuring by measuring the differential pressure over an orifice or a venturi pipe.
The differential pressure transmitter is also used to measure the water level in a steam boiler.
DISTILLATE FUEL OIL -- A light, volatile substance, such as No.2 oil, produced by fractional distillation of petroleum.
DO -- Diesel Oil. It is a distillate fuel oil and the distillation-curve lies between 200 and 350°C.
DONKEY BOILER -- Auxiliary boiler used to supply steam to deck machinery and engines for electric power while the ship is in port and the main boilers are shut down.
DONKEYMAN -- Person who tends a donkey boiler and auxiliary machinery equipment onboard ships.
DOWNCOMER -- A tube or pipe in a boiler circulating system through which fluid flows downward. These tubes are normally not heated, and the boiler water goes through them to supply the generating tubes.
DRAUGHT -- (1) The flow of air through a boiler furnace. (2) A measure of the degree of vacuum inducing air-flow through a boiler furnace.
DRAFT HOOD -- A device, usually integral to a furnace, which maintains furnace draft by admitting room air into the vent.
DRY-BACK BOILER -- A shell-type boiler with one or more furnaces passing to a combustion chamber at the back, from which an upper bank of firetubes leads to the uptake at the front. The combustion chamber is provided with a refractory lined back door that allow maintenance and inspection.
DRY PIPE -- (Internal Feed Pipe) A pipe running along the top of the steam space in which slots are cut in the top or sides for the purpose of admitting only dry steam to the line. One end of the pipe has a blank ending and the other end is connected to the steam outlet. Drainage holes are drilled along the bottom of the pipe.
DRY STEAM -- Steam containing no moisture. Commercially dry steam containing not more than one half of one percent moisture.
D SLIDE-VALVE -- A simple form of slide-valve, in section like a letter D, sliding on a flat face in which ports are cut.
DUMP CONDENSER -- Takes care of excess steam from the waste heat boiler when the steam production exceeds the steam demand.