Steam Main Jargon Buster

Nadrowski steam turbine

A type of steam turbine made by the Nadrowski company in Bielefeld, Germany. Nadrowski steam turbines are now part of the Dresser Rand company range.

Needle valve

A valve design to provide fine control of flow and is generally restricted to small sizes of pipes. The disc, commonly integral with the stem has a needle shaped end which fits very accurately into the body seat and the threads on the stem are made of finer pitch than usual to obtain close regulation of flow. Usually needle valves have a reduced size of orifice in relation to the pipe size.


This is name given to a length of straight pipe with male threads on both ends. It is a connector, or a coupling, threaded on both ends. Nipples are used to allow pipes and fittings to be inter-connected. Types of pipe nipples may include Barrel, Hexagon, Swage, and Weld.

Nominal pressure (PN)

PN stands for 'Pression Nominale' and is a numerical designation which is convenient for reference purposes. All equipment of the same nominal size (DN) designated by the same PN number, have the same mating dimensions.

Nominal size (DN)

DN stands for 'diametre nominal' and refers to the nominal diameter of a pipe in either metric or imperial terms. It is a convenient round number for reference purposes and is only loosely related to manufacturing dimensions.

Normally closed switch

A switch in which the contacts are normally closed. Actuation opens the contact.

Normally open switch

A switch in which the contacts are normally open. Actuation closes the contact

NPSH (net positive suction head)

The minimum suction pressure required by a pump to prevent cavitation.


An acronym for the National Pipe Tapered Thread. It is a standard for tapered threads used to join pipes and fittings from the USA. The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other. This is different from parallel/straight thread fittings or compression fittings in which the threads merely hold the pieces together. However NPT fittings must be made leak free with the aid of thread seal tape or a thread sealant compound.

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