Back flow preventing mechanism for writing implement

A back flow preventing mechanism for a writing implement having a writing tip and a fluid reservoir, the mechanism comprising:

• a coupling having a proximal end connected to the writing tip and a distal end connected to the fluid reservoir;
• a bore extending longitudinally through a portion of the coupling from the distal end;
• a valve chamber formed within the coupling;
• a seat insert fitted in the bore and defining a first fluid passage in fluid communication with the valve chamber, the seat insert providing a first opening into a distal end of the valve chamber and a valve seat at the first opening;
• a valve body loosely housed within the valve chamber and having a body diameter, the valve body preventing fluid back flow from the valve chamber to the first fluid passage through the first opening when borne against the valve seat;
• and
• a second fluid passage in fluid communication with both the writing tip and the valve chamber and providing a second opening disposed at the proximal end of the valve chamber, the second fluid passage having a generally oblong cross section that is sized relative to the valve body diameter so as to prevent the valve body from fully entering the second fluid passage and yet permit fluid flow to the writing tip when the valve body is borne against the second opening.

A writing implement comprising:

• a writing tip with a writing ball;
• an ink reservoir with a store of ink;
• a coupling having a proximal end connected in fluid communication with the writing tip and a distal end connected in fluid communication with the ink reservoir;
• a valve chamber formed within the coupling and having a generally circular cross section;
• a bore extending longitudinally through a portion of the coupling from the distal end to one end of the valve chamber;
• a seat insert fitted in the bore and defining a first ink passage between the ink reservoir and the valve chamber, the seat insert providing a first opening into the valve chamber and a defining valve seat at the first opening;
• a generally spherical valve body loosely housed within the valve chamber and having a body diameter, the valve body preventing ink back flow from the valve chamber to the first ink passage through the first opening when borne against the valve seat;
• and
• a second ink passage in fluid communication with both the writing tip and the valve chamber and providing a second opening to the valve chamber opposite the first opening, the second ink passage having a generally oblong cross section that is sized relative to the valve body diameter so as to prevent the valve body from fully entering the second ink passage and yet permit ink flow to the writing tip when the valve body is borne against the second opening.