Injector

A steam injector is typically used to deliver cold water to a boiler against its own pressure using its own live or exhaust steam, replacing any mechanical pump. This was the purpose for which it was originally invented in 1858 by Henri Giffard. Its operation was from the start intriguing since it seemed paradoxical, almost like perpetual motion. Its operation was later explained using thermodynamics.

Other types of injector may use other pressurised motive fluids such as air.

Depending on the application, an injector can also take the form of an eductor-jet pump, a water eductor or an aspirator. An ejector operates on similar principles to create a vacuum feed connection for braking systems etc..

The injector was invented by Henri Giffard for the steam locomotive and patented in the United Kingdom by Messrs Sharp Stewart & Co. of Glasgow.

After some initial scepticism resulting from the unfamiliar and superficially paradoxical mode of operation, the injector was widely adopted as an alternative to mechanical pumps in steam locomotives.

The injector consists of a body containing a series of three or more "cones" containing nozzles along one axis.

It uses the Venturi effect of a converging-diverging nozzle on a steam jet to convert the pressure energy of the steam to velocity energy, reducing its pressure to below atmospheric which enables it to entrain a fluid (eg. water). After passing through the convergent "combining cone", the mixed fluid is fully condensed releasing the latent heat of evaporation of the steam which imparts extra velocity to the water. The condensate mixture then enters a divergent "delivery cone" which slows the jet, converting kinetic energy back into static pressure energy above the pressure of the boiler enabling its feed through a non-return valve.

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Wikipedia