Steam jet ejectors are a reliable and economical means for producing vacuum. The primary advantages of the ejector design are its low initial cost, lack of moving parts, and simplicity of operation.
The conventional steam jet ejector has four basic parts; the steam chest, the nozzle(s), the mixing chamber and the diffuser. The diagram at left illustrates basic ejector operation: a high pressure motivating fluid enters at 1 and expands through the converging-diverging nozzle to 2; the suction fluid enters at 3 and mixes with the motivating fluid in the mixing chamber 4; both are then recompressed through the diffuser to 5.
Single-Nozzle Ejectors (right) are used for either critical or non-critical flow, but usually for only one set of design conditions.
Multiple-Nozzle Ejectors (right) are unique in both design and performance. In most cases, they offer steam savings of 10% to 20% when compared with single-nozzle units designed for the same conditions
Spindle-Operated Ejectors (right) are indicated whenever suction or discharge pressures vary. During operation, a pneumatically-driven tapered spindle moves in and out of the nozzle orifice to control motive fluid flow.