Editing Vacuum ejector (section)

=== Steam ejector ===
The industrial steam ejector (also called the "steam jet ejector", "steam aspirator", or "evactor") uses steam as a working fluid and multistage systems can produce very high vacuums. Due to the lack of delicate moving parts and the flow of steam providing somewhat of cleaning action, steam ejectors can handle gas flows containing liquids, dust, or even solid particles that would damage or clog many other vacuum pumps. Ejectors made entirely from specialised materials such as [[Polytetrafluoroethylene|PTFE]] or [[graphite]] have allowed usage of extremely corrosive gasses, since steam ejectors have no moving parts they can be constructed in their entirety from almost any material that has sufficient durability.

In order to avoid using too much steam or impractical operating pressures, a single steam-ejector stage is generally not used to generate vacuum below approximately 10 [[kPa]] (75 [[mmHg]]).<ref name="hv">''High Vacuum Pumping Equipment'', B. D. Power, New York: Reinhold Publishing Corporation, 1966, chapter 4.</ref> To generate higher vacuum, multiple stages are used; in a two-stage [[Injector|steam ejector]], for example, the second stage provides vacuum for the waste steam output by the first stage. Condensers are typically used between stages to significantly reduce the load on the later stages. Steam ejectors with two, three, four, five and six stages may be used to produce vacuums down to 2.5 [[Pascal (pressure)|kPa]], 300 Pa, 40 Pa, 4 Pa, and 0.4 Pa, respectively.<ref name="hv" />

Steam ejectors are also suitable for pumping many liquids since if the steam can be easily condensed into the liquid then there is no need to separate the working fluid or manage a mist of liquid droplets. This is the manner in which a [[steam injector|steam ''injector'']] operates.

An additional use for the injector technology is in vacuum ejectors in [[Railway brake|continuous train braking systems]], which were made compulsory in the UK by the [[Regulation of Railways Act 1889]]. A vacuum ejector uses steam pressure to draw air out of the vacuum pipe and reservoirs of continuous train brake. Steam locomotives, with a ready source of steam, found ejector technology ideal with its rugged simplicity and lack of moving parts. A steam locomotive usually has two ejectors: a large ejector for releasing the brakes when stationary and a small ejector for maintaining the vacuum against leaks. 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.