Vacuum Degasser are used to remove the small entrained gas bubbles left in the mud by the mud/gas separator. These units are positioned downstream from mud/gas separators, shale shakers and mud cleaners, while hydrocyclones and centrifuges follow in the arrangement.
Operational Theory: Vacuum degasser utilize negative pressure by vacuum pump to withdraw entrained gases from the mud. In order for this to work, mud is pumped through a venturi, which develops a negative pressure in the vessel by vacuum pump, thus sucking mud into the unit. The choice between horizontally- or vertically-mounted units is typically based on the footprint requirements of the specific rig.