1. Field of the Invention
The present invention relates to a writing instrument having a writing tip, in particular a tubular writing tip. The instrument also has a tank for writing fluid which can be pushed from behind, onto a cylindrical body which, on its forward end, carries a writing tubule, writing tip or the like. A compensating chamber means is in the vicinity of the instrument forward end, and is in sealing engagement with the cylindrical body. The ink compensating chamber means is a sheath body with an inner surface defining an inner compensating chamber that communicates, at its forward end, with a transverse bore provided in the forward end area of the cylindrical body, and into the inner bore of the cylindrical body. At its rearward end the inner, ink compensating chamber communicates, via a connecting bore, through the wall of the compensating chamber sheath body, with an outer ink compensating chamber provided about the outer surface of the compensating chamber sheath body. The outer compensating chamber is covered by a sheath element, and the forward end of the outer compensating chamber communicates with ambient air between this sheath element and the cylindrical body.
2. Brief Description of the Prior Art
In a known writing instrument of this type, which is illustrated in certain prior patents by ANDERKA (DE 30 09 100 C2, DE 30 09 169 C2, EP 35,736 and copending U.S. Ser. No. 06/529,654) a compensating chamber area is molded onto the forward end of the tank for writing fluid, so that both the writing fluid tank and the compensating chamber area can be mounted or pushed in common onto the cylindrical body, from behind. The outer compensating chamber is covered by a sheath element that is embodied as a separate piece from the cylindrical body and can be removed toward the front, so as to expose the outer compensating chamber.
In this known writing instrument, the user can clean the compensating chambers each time the writing fluid tank is refilled; as the writing fluid tank is removed for the purpose of refilling, the compensating chambers are exposed. If the writing fluid tank is embodied as a cartridge of writing fluid, such cleaning of the compensating chambers is not required. If one writing fluid cartridge is exchanged for another, clean compensating chambers automatically are put into place as well.
While this previously known writing instrument thus enables optimal cleaning of the compensating chambers, it has the disadvantage that the manufacture of a writing fluid tank, with a compensating chamber means provided on its forward end, is relatively expensive.
It is true that another writing instrument is known, as illustrated in certain prior patents by GLASA et al. (DE 21 59 522 and GB 1 322 477) in which inner and outer compensating chambers are embodied on a sheath body which can be inserted from the front, and into an annular chamber of a cylindrical body. In this known writing instrument the inner and outer compensating chambers are disposed in parallel, that is, their rearward ends are in direct communication with a transverse bore communicating with an inner bore. Furthermore, a special tool is required to remove the sheath body, which has a compensating chamber on both its inner and outer faces. Consequently, the user will only very seldom undertake to clean the compensating chambers.