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The New Zealand Railways Magazine, Volume 3, Issue 10 (May 1, 1929.)

Exhaust Steam Injector

Exhaust Steam Injector.

This injector acts as a feed water heater, and is, in principle, similar to the ordinary live steam injector, except that it uses the exhaust steam from the cylinders to heat the feed water and also to force it into the boiler. The use of exhaust steam in this way results in a saving of from 8 per cent. to 12 per cent. in coal and water, due to the return to the boiler of condensed steam. It function as a feed water heater so long as the locomotive is using steam, and when the engine regulator valve is closed it operates with live steam, automatically changing from exhaust to live steam working and back to exhaust steam when the regulator is again open. This automatic change-over is controlled by the pressure in the steam chest actuating
Illustration No. 2.

Illustration No. 2.

page 53 an automatic valve which shuts off the live steam supply when exhaust steam is available. (Illustration No. 3.) The injector consists of a casing which contains the exhaust steam inlet cone, supplementary live steam cone, and the combining and delivery cones, together with the water and overflow valves.

The exhaust steam from the cylinders is admitted in two separate stages. The first stage consists of a jet of steam admitted through a central cone, the condensing water being in the form of an annular jet surrounding the end of the steam cone. This steam, condensed by the water jet, imparts its momentum to it, and the mixture of steam and water flows forward at a high velocity through the second cone (known as the draft tube).

The proportion of steam to water is such that a high degree of vacuum is created within the draft tube. At the end of this tube the second supply of exhaust steam is admitted in the form of an annular jet. This gives a further impetus to the mixture, which then flows through the vacuum tube into the combining cone, where complete condensation takes place, and the whole of the available energy of the steam is transferred into work imparting velocity to the water jet.

Illustration No. 3.

Illustration No. 3.

Leaving the combining cone, the jet passes into the delivery cone, where this velocity energy is transferred into pressure energy, and, leaving the injector, it passes into the boiler.

A grease separator is fitted in the exhaust pipe line between the blast pipe and the injector. The duty of this unit is to remove any grease, dirt, or water, which may be carried along by the exhaust steam. It consists of a spherical casing, with inlet and outlet branches for the exhaust steam. At the bottom of this casing an automatic drip valve is provided through which the collected oil, water, etc., is drained off.