Abstract: In gas washer and similar separator devices which utilize stationary wall means to deflect a gas flow and to subject the same to centrifugal force for continuously separating out foreign particulate matter which is collected on or adjacent the stationary wall means, the invention provides spirally curved laminae constituting the stationary wall means and co-operating to define passage means, at least a part of which has a cross-section which first narrows and then widens in the direction of fluid flow and which is also curved spirally first in one and then in the opposite direction. Nozzle means may be arranged to feed moisture into the fluid flow to assist wet separation, and by electrically insulating conductive laminae from one another, the invention may also be used as an electrostatic precipitator.