cavitation

To remove the air you might try drawing a strong vacuum (>20"hg) on the fluid for a time to remove the air that is bound up in the fluid before putting it into the shock or before charging the shock with the gas. I dont know what type of gas you use but I would imagine the fluid will absorb some of that in place of the air and you may be back at square one. Hope there are some racers out there willing to help you.

your first post is like your first beer if you like it you'll have some more....

Basics first...aeration/foaming is caused whenever there is turbulance in the oil that allows for air passing through the oil. When the surface tension of the oil is larger than the forces of the air buble trying to get out of the oil you have have foaming. There is a basic ASTM test to determine the anti-foaming charistics of an oil. usually a little bit of Silicon ~ 3-6 ppm is put into the oil to lower the surface tension. More silicon will have just the opposite effect. It's like putting more soap in the bottle that kids use to blow bubbles. So you should be able to experiment with different oils to find the one with the lowest foaming tendancy's.
Cavitation - is caused when the air that is entrained in the oil enters a negitave pressure zone. The air rapidly expands and the result is either mechanical damage or undesirable performance. Normal solution is to remove the air or reduce the inlet pressure zone requirements. Sorry I can't explain that in the context of what's happening in your shock.

Most of us here are not engineers, they dont need to ask questins , they have all the answers. (just kidding)

Just thinking out loud but there should be some way of physically seperating the oil from the pressurised air in the shock with some type of an internal expanding bladder system.

regards......

thanks for your answers I couldn't get them earlier.
the shock absorbers are the type called DeCarbon, they are gas charged with nitrogen in a chamber that has a floating piston or a rubber bladder, so given the service interval of the parts there shoudn´t be any significant gas leak to the body of oil.
We will try the vacuum and I'll keep you informed, we are supposing that once the oil is taken to atmospheric it will not reabsorb any air. Mr. Wallace, you mention that cavitation produces mechanical damage, it is possible that the rapid expansion of the gas contained in the oil do generate a shock wave? or what is the cause of the mechanical damage?
Also you mention that the conditions of the inlet (and outlet i assume) plays a role in cavitation, we have been radiusing the inlet/outlet ports of the pistons (that move through the oil) to make the cross section transition less abrupt and get smoother response and fight cavitation. Do you know of some information regarding boundary layer separation vs. diverse inlet throat radius?
thanks again for your answers.

In the short period of time that the oil is exposed to atmospheric pressure it should not absorba a significant amount of air unless it is agitated a signifacant amount. I will be looking for you findings.