A gas separator sits between the intake and the first pump stage and diverts free gas into the annulus instead of letting it enter the impellers.
Why it matters
Free gas reduces the density of the pumped fluid. Above a certain fraction the impeller loses its ability to build head at all, which is the condition known as gas lock.
Types
Static separators rely on the change of flow direction, while rotary separators spin the fluid so heavier liquid moves outward and gas concentrates near the shaft.