Selective wetting of a roller

A flow unit for installation in a wetting apparatus to locally disrupt supply of liquid agent from a lip of an applicator unit over a gap to a wettable roller surface of a roller for selective wetting of the roller surface, the flow unit comprising:

• an elongate nozzle to direct a planar gas jet along a jet direction normal to a first axis;
• and
• a flow guide having an axial extent along the first axis which is less than the axial extent of the nozzle along the first axis;
• wherein the flow guide is to direct an axial portion of the gas jet into a corresponding regulated axial portion of the gap to locally disrupt supply of liquid agent to the roller surface, thereby preventing wetting of a corresponding axial portion of the roller surface.

A flow unit kit for installation in a wetting apparatus to locally disrupt supply of liquid agent from a lip of an applicator unit over a gap for selective wetting of a wettable roller surface of a roller, the flow unit kit comprising:

• an elongate nozzle to direct a planar gas jet along a direction normal to a first axis;
• a flow guide support;
• and
• a plurality of flow guides each mountable to the flow guide support to direct an axial portion of the gas jet into a corresponding regulated axial portion of the gap to locally disrupt supply of liquid agent to the roller surface, thereby preventing wetting of a corresponding axial portion of the roller surface;
• wherein at least two flow guides have different axial extents along the first axis when mounted to the flow guide, thereby permitting assembly of a flow unit having a selected one of the flow guides to prevent wetting of a portion of the roller surface having a corresponding axial extent.