Workflow conditions

Hi Team. 

Having some mental blanks today. 

I have a VA on the users account that they will type a DeviceID in to it. The VA is a DirectoryString

Now what i am trying to do is this. 

1) Any text that is entered in to the VA then kicks off an approval rule. 

2) If there is already text in the VA and i want to blank the data that it just does it and there is no approval rule for this. 

I have tried a few things but all seem to kick in the approval rule on blanking the VA but not when putting data in. Any suggestions, i must be missing something., 


Thanks in advance