This is not a theory. Anyone that understands hydraulics knows that air will always seek the top in a liquid. An example would be hot water pipes in a home where the air seeks the top of a radiator where the bleeder is. You could never get that air out of the lines from the basement no matter how hard you pushed. If you ever siphoned gas with a clear tube you will notice a bubble of air at the top of the tubing will stay there even while the liquid still flows. So you can't push the air from the top of the damper out the head because it is lower than the liquid.
Yes I agree if you blow air in the damper it flows both ways. But that valve you are talking about is a check valve that is made to work with liquid not air. If you shake the damper you can hear it rattle. Check valves are used to control flow direction and to stop back flow.
The one way air valve I am talking about is the damper itself. It is the soft membrane ( Clear Plastic) that is on one side of the damper. The soft clear flexible piece. You can not do a test with it because it is microscopic. If you look at the plastic under a microscope or a good magnifying glass you can see there are pores in it. The membranes allow air to escape in one direction but do not allow fluids with larger molecules to escape. Why else do you think this little piece of plastic cost so much.
Here is a design for a HP damper and membrane. When I find the Roland damper design I will post them.
An air accumulator (damper) can be incorporated in the ink supply line adjacent the connector needle to trap any air that may transit the ink supply line and comprises a riser and an air valve formed of a porous membrane which allows air to pass therethrough, but will not allow ink or other liquids to pass through. A layer of liquid over the membrane prevents air from entering the accumulator in the reverse direction, even if a sub-atmospheric pressure exists within the accumulator. A relatively viscous non-volatile liquid, such as glycol for example, is used to cover over the membrane in this way. A cover plate incorporating a small opening to allow escape of air, closes the top of the riser. Alternatively, or in addition, to the provision of the layer of liquid, a check valve such as a flapper or duck-bill valve, biased to a closed position, can be provided. The check valve controls the opening on the cover plate to allow escape of air from the riser and prevent air from being drawn into the riser if the pressure in the riser drops below atmospheric. In a further alternate embodiment in place of the membrane one-way air valve a float valve could be employed, and, as will be apparent, a biased closed check valve such as described above must also be used therewith to prevent introduction of air into the riser when a vacuum is drawn on the interior of the riser sufficient to overcome the buoyancy of the float of such a valve.
