Settler or sometimes known as decanter, can be very simple, where the entering liquid is dispersed into droplets.
The droplets are then allowed to settle by gravity in the main part of the vessel. Most settlers consist of a horizontal vessel, because the separating efficiency is proportional to the area of the phase interface.
To increase the size of the droplets and hence their settling rate, the dispersion may be passed through a coalescer (packing or wire mesh).
There are two types of settler: