This is one of those things where if you have the behavior, it might help. If you don't experience this issue, you'll wonder if I've bumped my head on something.
My metal blast gates have a little stud knob to lock them in the open or closed position. My DC tends to suck the gate halfway closed if it is not held in the open position. I didn't like bothering with the turn-knob, especially if I were opening or closing the gate with a stick from a distance (as I normally do; custom built stick . . . even too silly to show here).
Remove the knob and get yourself a small barrel shaped magnet and a screw that will fit but not extend into the gate path; that is . . . a short one.
Mill your 'precision magnet placement appliance' into the proper dimensions and form.
Screw it on where the knob used to be.
and now . . . the gate stays closed (it used to do that anyway but it makes this sound more exciting than it actually is).
And the gate stays open (it didn't used to do that without turning the locking knob).
So, now I'm all happy and you all are thinking of banning me from the forum.