In RO system architecture, a "stage" is a group of pressure vessels arranged hydraulically in series so the concentrate of one feeds the next. A "pass" sends the permeate of one full RO step into the feed of another for further purification. A two-stage system (e.g., 6:3 array) routes the concentrate of stage 1 (six vessels) into stage 2 (three vessels), maintaining crossflow as flow drops. A two-pass system feeds permeate of pass 1 to a second RO array for ultra-low TDS output. Multi-stage arrays let brackish systems achieve 75–85% recovery while keeping element crossflow within spec. Multi-pass systems achieve permeate <10 ppm TDS for boiler feed or semiconductor rinse. When permeate TDS target is below what a single pass can deliver — typically < 50 ppm from brackish or < 100 ppm from seawater feed. Most SWRO is single-stage at 40–45% recovery. Brackish systems are typically 2-stage at 75–85% recovery. Six pressure vessels in stage 1, three in stage 2, all feeding from a common HP pump. The 2:1 reduction maintains element crossflow as flow drops 60% across stage 1. ForeverPure has supplied desalination, high-pressure pumps, and energy-recovery devices to commercial and industrial customers since 2003. Contact our engineers for sizing, quotes, or technical support.Pass and Stage
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