Four, Five and Six Stage Steam Jet Ejector
Principle of Operation
Four, Five and Six Stage Steam Jet Ejector units are used for applications where required suction pressures are beyond the range of the ejectors previously described. Generally, suction pressure ranges are as follows:
- Four-Stage Ejectors – 4 mm Hg. abs. to 75 microns Hg. abs.
- Five-Stage Ejectors – 0.4 mm Hg. abs. to 10 microns Hg. abs.
- Six-Stage Ejectors – 100 microns Hg. abs. to 3 microns Hg. abs.
Four-stage units consists of (1) a primary booster ejector; (2) a secondary booster ejector; (3) a high vacuum ejector; (4) a low vacuum ejector; and (5) usually two condensers—one after the secondary booster ejector and the other between the high vacuum and low vacuum ejectors. The condenser between the high and low vacuum ejectors is sometimes omitted, depending upon application requirements. Direct contact or surface condensers, arranged barometrically or at ground level, can be used.
The four-stage is similar to the three-stage unit except that another booster ejector is added. In the four-stage, the primary booster is steam-jacketed to prevent build-up of ice on the diffuser internal bore.
The five and six-stage units are similar in appearance to the four-stage ejector except that additional booster ejectors are added. While four, five, and six-stage ejectors are usually condensing types for reasons of efficiency and operating economy, it is possible to employ non-condensing types.