Injector
An ejector operates on similar principles to create a vacuum feed connection for braking systems etc.
It is a typical application of the injector principle used to deliver cold water to a boiler against its own pressure, using its own live or exhaust steam, replacing any mechanical pump.
After some initial scepticism resulting from the unfamiliar and superficially paradoxical mode of operation,[6]: 5 the injector became widely adopted for steam locomotives as an alternative to mechanical pumps.
[6]: 5,7 Strickland Landis Kneass was a civil engineer, experimenter, and author, with many accomplishments involving railroading.
The delivery tube is a diverging duct where the force of deceleration increases pressure, allowing the stream of water to enter the boiler.
Injectors exist in many variations, and can have several stages, each repeating the same basic operating principle, to increase their overall effect.
Other key properties of an injector include the fluid inlet pressure requirements i.e. whether it is lifting or non-lifting.
In a non-lifting injector, positive inlet fluid pressure is needed e.g. the cold water input is fed by gravity.
[10] 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).
Injectors can be troublesome under certain running conditions, such as when vibration causes 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.
Another common problem occurs when the incoming water is too warm and is less effective at condensing the steam in the combining cone.
The internal parts of an injector are subject to erosive wear, particularly damage at the throat of the delivery cone which may be due to cavitation.
[13] An additional use for the injector technology is in vacuum ejectors in continuous train braking systems, which were made compulsory in the UK by the Regulation of Railways Act 1889.
The exhaust from the ejectors is invariably directed to the smokebox, by which means it assists the blower in draughting the fire.
The small ejector is sometimes replaced by a reciprocating pump driven from the crosshead because this is more economical of steam and is only required to operate when the train is moving.
The sketch on the right shows a cross section through a smokebox, rotated 90 degrees; it can be seen that the same components are present, albeit differently named, as in the generic diagram of an injector at the top of the article.
Exhaust steam from the cylinders is directed through a nozzle on the end of the blastpipe, to reduce pressure inside the smokebox by entraining the flue gases from the boiler which are then ejected via the chimney.
The effect was first noted by Richard Trevithick and subsequently developed empirically by the early locomotive engineers; Stephenson's Rocket made use of it, and this constitutes much of the reason for its notably improved performance in comparison with contemporary machines.
The major advantage of jet pumps for deep well installations is the ability to situate all mechanical parts (e.g., electric/petrol motor, rotating impellers) at the ground surface for easy maintenance.
Finally the booster is operated (in conjunction with the HV & LV ejectors) to pull vacuum to the required pressure.
