Originally Posted by IanU
The pressure will decrease as the tank cools, not increase.
Yes, but what he means is the end result is a higher pressure (more air in the tank). If you fill slowly the tank won't heat up as much therefore you won't lose as much pressure as it cools. e.g. if you fill to 200 quickly, the recipient vessel warms up, and by the time it's cooled back to ambient you might only have 190 in there (figures for example only). Fill slowly and you'll get much closer to 200.