Fountain Pens Leak!

Of course they do, otherwise they wouldn't write. It's a complaint that arrives with a small percentage of pens received for repair each week; the majority turn out to have no real problem.

The main cause of a real problem leak is where air is entering the filling system. Perished rubber sacs and membranes are the main culprits here, but badly fitting cartridges (aren't they always?), possibly old stock, are also problems.

Circumstantial leaks are usually caused by air in the filling system expanding and pushing ink out. This happens with increased air pressure when flying, or from heat (often body heat from wearing the pen in a shirt pocket). Oversize ink sacs, and less than full pens (have you noticed how your pen writes wetter when near empty), both increase the incidence of this problem.

A further circumstantial leak occurs with impact (dropping the pen, or a handbag containing the pen). Ink is expelled into the inner cap surrounding the nib and in contact with the grip section. If this is not cleaned out, ink will continue to be drawn out of the pen by natural capillary attraction.