PSI is the variable that stored the value of the air pressure.
I need to make sure that this value is increasing. If I can
get a good example on how to do it, I will then adjust the
TIME vs the PSI for 10 PSI each 20 seconds more or less.
You need two variables - one for the current PSI and one for the previous PSI.
Each time you read from the sensor, you get the current PSI value. It isn't rocket science to compare the current value to the previous value. It isn't rocket science to determine whether the change is significant enough to continue, or is small enough to warrant shutting off stuff.
At the end of loop(), the current value becomes the previous value.