Tray drain holes must empty all trapped liquid after shutdown without creating unacceptable vapor bypass during operation. Design them from actual low points, falling-head drainage time, fouling risk, seal integrity and the maintenance procedure.

Riser height protects the liquid seal, while cap-slot area and elevation control vapor velocity, activation pressure and pressure drop. Bubble-cap trays can provide strong low-load performance, but only when cap geometry, liquid gradient, levelness and fastening are controlled together.

Dual-flow trays offer simple, open construction, high capacity and strong fouling resistance but may have narrower turndown and more backmixing. Crossflow trays use downcomers to provide separate liquid transfer, generally improving stability and design flexibility.

Erosion and corrosion can enlarge, distort or block individual gas-distributor outlets, changing flow balance before leakage occurs. Inspect outlet geometry as well as wall thickness, then recalculate distributor hydraulics using the measured condition.

Prevent branch-pipe fatigue by identifying hydraulic and acoustic excitation, controlling unsupported spans, separating natural frequencies from operating excitation and inspecting fatigue-sensitive welds and supports. A steady-state pressure-drop calculation alone is insufficient.