Steam Main Jargon Buster

Data dossier

A record of the design and construction of a piece of important equipment.

De-ioniser

A piece of equipment used to remove the ions of dissolved salts from water.

Dead leg

A part of a pipe or system that is redundant to flow, but still exists in the system.

Deaeration

This is the process of removing air and other gases from the boiler 'feedwater' prior to it going into the boiler. This has numerous benefits.

Decibel

A logarithmic measure most commonly used for measuring sound.

Dehumidification

The removal of water vapour from air. This is done by the condensation of water vapour from air by cooling below the dew point or removal of water vapour from air by chemical or physical methods.

Delta Steam Systems

A company which manufactures a venturi orifice type steam trap which has no moving parts. The company is based in South Africa.

Density compensation

This is required in steam metering where the density of steam is determined by sensing pressure or temperature (or both), to enable the computer to provide a mass flow result from a volumetric figure.

Derivative control

A type of control signal. It measures and responds to the rate of change of the process signal and makes adjustments to minimise overshoot.

Desuperheater

A system which converts superheated steam back to saturated steam (or near to saturated steam temperatures). There are two main types; indirect contact and direct contact desuperheaters.

Dew point

This is the temperature at which droplets of water will condense out of its vapour state in boiler flue gases. The dew point is dependent on a number of factors, for example; temperature, pressure, fuel type and sulphur content.

DHW

Domestic hot water. A water system commonly used for taps, sinks, showers, and baths. Typically a temperature of 60 ° 65 °C is used.

Differential pressure

The difference in pressure between two points in a system.

Diffuser

A device which is fitted after a blast discharge trap, it diffuses the discharge and reduces noise.

DIN standards

An acronym for the Deutsches Institut fur Normung. They provide standards for industry in mainland Europe to drive standardisation. In a steam system examples of this would be; pipe fittings (e.g. flanges) and pipework.

Direct acting pressure reducing valve

A type of valve which is used to reduce the pressure of the medium going through it. The controlled pressure acts through a diaphragm, piston or bellows, on an imposing force from a compressed helical spring, weight, or weighted lever, or from compressed air. The construction is simple and robust. Such a valve can provide long life with maintenance free operation even under adverse working conditions. It is however not as accurate as a pilot operated type of valve.

Dosing

This is the adding chemicals to a system by a controlled operation.

DP17

Model number for a type of pressure reducing valve manufactured by Spirax Sarco. Usually used on steam (a version can be used on some gas applications), it is a pilot operated type pressure reducing valve (please also see pilot operated pressure reducing valve).

DP27

Model number for a type of pressure reducing valve manufactured by Spirax Sarco. It is a development of the DP17 with a modified design top end. Usually used on steam (a version can be used on some gas applications), it is a pilot operated type pressure reducing valve (please also see pilot operated pressure reducing valve).

Dresser Rand

A manufacturing company, best known in the steam industry for their range of steam turbines.

Droop

A word used to describe the difference between the set point and the actual operating or control point. It is typically taken into consideration when sizing and selecting direct acting pressure reducing valves.

Dryness fraction

A measure of the dryness of the steam. It is not always possible to produce 100% dry steam from a boiler, and keep the steam dry throughout the distribution system. Therefore this is a way of measuring the quality of the steam.


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