Bought and installed these when setting up dust collection in my woodshop.  Huge problem with these is that they trap sawdust and particles in the slot that the gate travels in.  The only way to clean out the slot is to remove the hose connected to it and use some type of wire to scrape out the debris.  I am considering cutting off the bottom of these so that the debris will fall out of the bottom and use tape to "re-close" them when in use.