Answer by
LeheckaG (1826)
A steam injector utilizes a pressurized steam nozzle
to draw up water into a converging inlet nozzle,
and then utilizes the Venturi effect via a diverging outlet diffuser
to force the mixture into a steam boiler.
Schematically:
steam ->-motive-nozzle-> water ->-converging-inlet-nozzle->-diverging-outlet-diffuser- >=> boiler