Injector
（重定向自Ejector pump）
![Diagram of a typical modern ejector.](/Images/godic/202501/10/Ejector_or_Injector1310.png")
1310.jpg")
![A- Steam from boiler, B- Needle valve, C- Needle valve handle, D- Steam and water combine, E- Water feed, F- Combining cone, G- Delivery nozzle and cone, H- delivery chamber and pipe, K- Check valve, L- Overflow](/Images/godic/202501/10/Injector_Giffard-021310.jpg")
![A more modern drawing of the injector used in steam locomotives.](/Images/godic/202501/10/Boiler_Feed_Injector_Diagram.svg1310.png")
An injector, ejector, steam ejector, steam injector, eductor-jet pump or thermocompressor is a type of pump. There are two varieties of injector, non-lifting and lifting.
The non-lifting injector cold water input is fed by gravity. It uses the principle of induced current (Impulse (physics)) to push water up to the boiler check valve. It avoids the premature boiling of feed water at very low absolute pressure, by avoiding the Venturi effect. The steam cone minimum orifice diameter is kept larger than the combining cone minimum diameter. The non-lifting Nathan 4000 injector used on the Southern Pacific 4294 could push 12,000 US gallons (45,000 L) per hour at 250 psi (17 bar).