What can I do to prevent beer staling in a keg being pushed by air? On a private party or picnic when we use hand pump to push beer out of a keg the beer can relatively quickly get stale. What can be done to keep the beer in a good quality for as long as possible?

I can imagine that a low temperature and not moving the keg can help. What about air pressure? Is it better to keep it low or higher? I guess that low pressure is better because lower amount of air should dissolve in the beer in such a case. What other factors could influence the beer durability in such a situation?
Avoiding agitating the beer and reducing the temperature are the two key ways to slow down the rate of staling, but really once there's air in the beer it's just a matter of time before it goes bad.

Have you considered using a small CO2 charger like this - 



This uses small CO2 cartridges to push the beer. The advantage being that the keg won't stale quickly since very little air is introduced.