Injector used in steam locomotives. Other types of injector may use other pressurised motive fluids such the reciprocating pump theory design and use pdf air. 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. 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. Most of the heat energy in the condensed steam is returned to the boiler, increasing the thermal efficiency of the process. The motive fluid may be a liquid, steam or any other gas. The entrained suction fluid may be a gas, a liquid, a slurry, or a dust-laden gas stream. Fluid feed rate and operating pressure range are the key parameters of an injector, and vacuum pressure and evacuation rate for an ejector. Other key properties of an injector include the fluid inlet pressure requirements i.
In a non-lifting injector, positive inlet fluid pressure is needed e. The steam-cone minimal orifice diameter is kept larger than the combining cone minimal diameter. The lifting injector can operate with negative inlet fluid pressure i. It differs from the non-lifting type mainly in the relative dimensions of the nozzles. Efficiency was further improved by the development of a multi-stage injector which is powered not by live steam from the boiler but by exhaust steam from the cylinders, thereby making use of the residual energy in the exhaust steam which would otherwise have gone to waste. Injectors can be troublesome under certain running conditions, when vibration caused the combined steam and water jet to “knock off”. Later injectors were designed to automatically restart on sensing the collapse in vacuum from the steam jet, for example with a spring-loaded delivery cone.