Braking device for a flat element in sheet form and method for cleaning such a device

A braking device for braking a rear portion of a flat element in sheet form when the sheet is displaced over a surface by pulling a front portion of the sheet, the braking device comprising:

• a suction device including the surface;
• the surface having at least one suction hole located to open at the surface over which the sheet is being advanced;
• the suction device having an air exhaust orifice through which suction air exits the device and an air circulation duct which communicates between the suction hole and the exhaust orifice;
• a principal compressed air injection device configured and located to supply air to the circulation duct and in the direction of the exhaust orifice, the principal air injection device is configured to generate a principal pulsed air flow past the suction hole and the principal pulsed air flow is capable of creating a Venturi effect for generating a braking suction air flow through the suction hole and into the circulation duct;
• a secondary compressed air injection device configured and located for generating, in the circulation duct and through the exhaust orifice a secondary pulsed air flow which is capable of creating the Venturi effect and of thereby generating a cleaning suction air flow through the corresponding suction hole.