The present invention relates a three phase separator or settling device (2) or a digester (1) comprising the settling device (2). The settling device can receive a fluid containing liquid, gas and particulate material. The settling device (2) comprises a settling chamber (3) which is to be filled with this fluid. The device can also comprise a liquid-discharge (5) for discharging liquid from the settling chamber and fitted close to the liquid level (30), a fluid inlet (6) for supplying the fluid into the settling chamber (3), a particulate material separation device (7) and a sludge outlet (8) from the settling chamber (3). According to a method of the invention a flow of fluid is provided into and out of the settling device (2) and settling chamber (3). According to an aspect of the invention the inlet (6) to the settling chamber (3) comprises a gas separation device (4) for separating gas from the fluid comprising channels, said inlet (6) positioned close to the fluid level (30). According to a further aspect the inlet (6) and transition (75) into the settling chamber is arranged to create a pre-separated flow pattern comprising a generally laminar liquid flow.