Tray spacing provides room for froth disengagement, downcomer backup, internal hardware and maintenance. Spacing that is too small can increase entrainment and flooding, while excessive spacing increases vessel cost without automatically improving separation.

Tray active area controls vapor velocity and entrainment, while downcomer area controls liquid handling, vapor disengagement and backup. Both areas must be rated together because increasing one normally reduces the other inside a fixed tower diameter.

Movable tray valves must be checked for correct type, orientation, retention and free travel. Stuck-closed valves restrict vapor capacity, while stuck-open valves promote low-rate weeping; functional inspection is therefore required before tower closure.

Sieve tray open area determines vapor velocity through the deck, while hole diameter controls the number, spacing and fouling behavior of vapor entry points. Both must be rated with tray liquid hydraulics across minimum and maximum operating rates.

An out-of-level tray creates deep liquid on one side and shallow liquid on the other, leading to simultaneous local flooding, vapor bias and weeping. Deck, support and weir elevations must be surveyed separately against the minimum operating liquid depth.