Abstract: An ink pen is provided with a hydrophobic membrane to control the leakage of ink. The ink pen has a vent, such as a bubble generator, to allow the ingress of air into the ink reservoir and thereby regulate the backpressure within the reservoir. The hydrophobic membrane which allows the flow of air but prevents the flow of ink is positioned within the vent to control leakage of ink from the ink pen through the vent.

Abstract: The back pressure of an ink pen is maintained by providing a capillary member adjacent a bubble generator. Regardless of the orientation of the pen, the capillary member maintains a quantity of ink adjacent an orifice defined by the bubble generator. The quantity of ink serves to supply a liquid seal formed in the orifice. As the back pressure within the ink pen rises to its maximum level, the liquid seal within the orifice is overcome and ambient air bubbles into the reservoir to lower the back pressure. As the back pressure returns to a desirable point, ink trapped by the capillary member enters the orifice to reseal the orifice.