\Hey Ira,
Hows the Magnesium?
And.....If you turn the switch on the skimmer on and off slowly while checking the performance, you will notice the skimmer bubbles up hard at one time and bugger all the next time. (The air tap needs to be fully open while doing this).
If you see no difference and it is bubbling profusely, the flap is ok.
If you see it changing , you either should remove the flap or flick the switch each time to get it right.