Use an inlet weir only when the tray needs controlled liquid spreading, jet reduction, sealing or a defined receiving zone. Check added downcomer backup, vapor interaction, turndown, drainage, fouling and end-gap distribution.

Estimate downcomer backup from tray liquid depth, weir head, tray pressure difference, downcomer and bottom-outlet losses, receiving conditions and aeration. Compare physical backup height with real available tray spacing plus a defined margin.

Recessed inlet sumps reduce downcomer outlet resistance by lowering the receiving floor and smoothing liquid entry onto the tray. Size the complete escape path and verify backup, vapor interaction, drainage, fouling, structure and clearance to the tray below.

Swept-back outlet weirs can increase high-liquid-load tray capacity by extending the effective crest and easing entry into the downcomer. Verify the complete flow path, turndown behavior, dead zones, active area and retrofit constraints.

Use a picket-fence weir when a full-width crest produces too little liquid head at minimum load. Size the gaps across the complete operating range and verify maximum-rate backup, froth interaction, fouling resistance and actual crest level.