Strickland Landis Kneass was a civil engineer, experimenter, and author, with many accomplishments involving railroading.  Kneass began publishing a mathematical model of the physics of the injector, which he had verified by experimenting with steam.  A steam injector has three primary sections:
*Steam nozzle, a diverging duct, which converts high pressure steam to low pressure, high velocity steam
*Combining tube, a converging duct, which mixes high velocity steam and cold water
*Delivery tube, a diverging duct, where a high velocity stream of steam and cold water become a slow high pressure stream of water