Bubble Cap applys in low gas/liquid loading condition.

Metal Bubble Cap/Tower Internals:

Bubble Cap Tray has riser or chimney fitted over each hole, and a cap that covers the riser. The cap is mounted so that there is a space between riser and cap to allow the passage of vapour. Vapour rises through the chimney and is directed downward by the cap,finally discharging through slots in the cap, and finally bubbling through the liquid layer on the tray.