A desilter is a type of mud recycling equipment that is designed to remove particles ranging in size from 15-25 microns.They do this through a collection of hydroclones that use centrifugal force and screens which filter out particulates that are found in the drill fluid after leaving the annulus. It is placed in line after the drill fluid (mud) has passed through the shale shaker, degasser and desander, but before the mud cleaner, centrifuge canter and mud agitator.
Trenchlesspedia Explains Desilter
The size and number of hydroclones on a desilter depend on the volume of the mud system, various sizes of hydroclones are available. A hydroclone has no moving parts, using only the geometry of the hydroclone itself and the velocity of the mud flowing in through the side to filter out heavier matter through the bottom and the lighter liquid up through the top. Both desilters and desanders, which filter out material 40-50 microns in size, are installed above a mud tank.