Minimal-compression butterfly valve

A butterfly-type valve for controlling toner material flow to a toner container, comprising:

• a valve plate which is pivotally disposed in an elongate flow path defined by a passage way, wherein the valve plate is pivotal from a closed position which substantially closes a fluid communication along the path to an open position which maximally permits fluid communication along the path,
• said valve plate having an outer diameter substantially smaller than an inside diameter of said passage way defining a gap area surrounding the circumference of said valve plate when said valve plate is in said closed position, said gap area having a predefined spacing to allow said toner material to flow without compressing said toner material within said gap area, and
• a pump for supplying negative air pressure to said gap area, wherein said toner material is attracted to said gap area forming a bridge of toner material in said gap area to substantially stop toner material flow in said gap area when said valve plate is in said closed position and said pump is enabled, and
• wherein said valve plate includes a porous member about the perimeter of said valve plate.