Suction brake, sheet conveyor with such suction brake and method of applying a retardation force to a moving sheet of material

A suction brake for use with a sheet conveyor configured to convey a succession of flat elements in sheet form along a conveying path between a first location and a second location, the suction brake comprising:

• a hollow body having an interior cavity and a face that defines a plurality of suction apertures that communicate with the interior cavity;
• and
• an obturator arrangement coupled to the hollow body and moveable with respect to the suction apertures;
• the obturator arrangement being moveable between an open position, in which the obturator arrangement exposes the suction apertures to a maximum extent, and a restricted position, in which the obturator arrangement occludes the suction apertures to a maximum extent,
• wherein the hollow body comprises a Bernoulli device and the suction apertures are provided by the Bernoulli device, and
• wherein the obturator arrangement is configured to undergo rotation when moving between the open and restricted positions.