Return to Return to Chapter 2 Main Page  Tray Components   The
function of a weir is to maintain a desired liquid level on the
tray. Typical weir height is between 2 - 4 inches. Low weirs are
frequently used in low pressure or vacuum columns. Notched
(rectangular or V-shaped) weirs are commonly used for low liquid
loads. see the Figure below for some examples:  Weir types  The
higher the liquid level, the higher the tray pressure drop.
Higher liquid level also imply more liquid hold-up on the tray,
which may be undesirable if the liquid is toxic or hazardous.  [
Back on Top ]    Downcomers are used to guide liquid flow from
an upper tray to a lower tray. The most common is the segmental-
type, which can be either straight or sloped (angled). See the
Figure below.  Downcomer types  The straight, segmental,
vertical downcomer is widely used as it provides good
utilization of column area for downflow and has cost and
simplicity advantage. Sloped downcomer can be used if vapour-
liquid disengagement is difficult (e