Ordering text field 1,2,3,4 instead of 1,10,11,12,2,3

Part of my application saves calibration results for gas pumps. I need to save pump numbers as a text field because you cannot input a negative number (-1) from the iPhone keyboard unless the field is a text field. This is only a problem because when I display the data I need the pumps to be in order of 1,2,3,4, etc, but right now they are sorting the pumps 1,10,11,2 ,4, etc.

Add a 0 to the front of any number under 10 like: 01, 02, 03, 04, etc.