This page is credited in full to Dave Cushman who created it. His voice is expressed in black colour text and any additions or comments in blue belong to myself. Credit: Dave Cushman’s website.
This method has been used in conjunction with porter escapes to allow the beekeeper to permit the return of bees by an uninterrupted path. This is mainly so that ‘wet’ supers that have been extracted can be returned to the bees for cleaning up.
The blade that closes the hole has been made from tinplate in the past, but the ones we used to make at Apex Enterprises had anodised aluminium slides. The slot and area that the blade slides over are treated with Petroleum Jelly so that any propolis, that the bees try to apply, will not stick.
I think this is overly complex and a simple board with a hole will work fine, a clearer board with the clearing aspect removed for instance. Always keep it as simple as you can.