Back flow preventing mechanism for writing implement

摘要

A mechanism for a writing implement prevents back flow of writing fluid from a writing tip back to a fluid reservoir of the implement. The mechanism has a valve chamber with a proximal end and a distal end. The mechanism also has a valve seat disposed at the distal end of the valve chamber. A first fluid passage in the writing implement defines a first opening into the valve chamber at the valve seat. The first fluid passage is in fluid communication with both the fluid reservoir and the valve chamber. A valve body has a body diameter and is loosely held within the valve chamber. The valve body prevents fluid back flow from the valve chamber to the first fluid passage when borne against the valve seat. A second fluid passage in the writing implement is in fluid communication with both the writing tip and the valve chamber. The second fluid passage has a second opening disposed at the proximal end of the valve chamber. The second fluid passage has 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 entry of the second fluid passage.