Overall, trayed columns operate via countercurrent liquid and vapor flow, with staged
contacting for heat and mass transfer. Each stage is often modeled as a mixer-separator, with liquid-vapor contacting followed by the separation of liquid and vapor to the stages below and above respectively. This description is somewhat oversimplified because the liquid actually flows flows across the tray, creating a concentration gradient.

As in a packed columns, gravity is the driving force for liquid down flow, and pressure differential moves the vapor up through the trays. The surface area for mass transfer is  provided by the bubbles and droplets generated by the injection of the vapour into the cross-flowing liquid. This differs from what occurs in the packed column, where the wetted packing provides much of the surface area for mass transfer.

Trays normally are designed to operate at liquid flow rates between 2 - 8 gal/min per inch of outlet weir length. At lower flow rates significant liquid entrainment into the higher tray and down comer (relative to the total liquid flow across the tray ) can reduce the liquid holdup on the lower tray.

Liquid flow rates higher than 12 gal/min per inch of outlet weir increase the liquid crest over the weir, adding to the liquid level on the tray. A higher level raises the tray pressure drop boosts the tendency of liquid weeping through the vapor flow openings. Vapor flow is bounded on the low side by that required efficient liquid - vapor contacting and weeping prevention. Conversely, a higher vapor flow rate hikes tray pressured drop, abetting entrainment, and may eventually lead to column flooding.

Trays can operate in a continuous vapor regime (with small droplets of liquid dispersed in the vapor above the trays) or in a continuous liquid regime (with bubbles dispersed in the liquid). Although operating rate is also a factor, the former condition is characteristic of vacuum columns and the latter of high pressure and high liquid flow rate columns. "Sieve trays are less expensive than bubble-cap or valve trays because they are the simplest to make".