Pen with slide plug and valve

Claim 1

Apparatus having a cylindrical casing and a writing tip provided on its forward end portion and adapted to supply liquid at a predetermined position, said writing tip producing a sucking pressure for sucking ink from inside the apparatus when used, said apparatus comprising: a main ink reservoir formed within said cylindrical casing; a slide plug slidably inserted within said main ink reservoir and separating ink within said main ink reservoir from air, said slide plug having a predetermined sliding resistance and being communicable with a sliding pressure sufficient for permitting the slide plug to slide in spite of the sliding resistance; a sub ink reservoir having a small capacity and communicating with said writing tip; and a valve mechanism comprising means through which said main ink reservoir communicates with said sub ink reservoir and which includes a valve body, said valve mechanism being normally closed, and being opened when a differential pressure between the pressure in the main ink reservoir and the pressure in the sub ink reservoir becomes higher than a predetermined valve opening pressure, thereby supplying ink from the main ink reservoir into the sub ink reservoir, said sliding pressure of the slide plug and said valve opening pressure of the valve mechanism being determined such that their sum is smaller than the sucking pressure at the writing tip, wherein there is no air in said sub ink reservoir.