An injector is a system of ducting and nozzles used to direct the flow of a high-pressure fluid in such a way that a lower pressure fluid is entrained in the jet and carried through a duct to a region of higher pressure. It is a fluid-dynamic pump with no moving parts except a valve to control inlet flow.
A common device used for delivering water to steam boilers, especially in steam locomotives is a steam injector. It is a typical application of the injector principle used to deliver cold water...