Why, don't you know? Need someone else to tell you? Told you, I don't use google, never have. In short though air gaps are a form of backflow protection, which type would be suitable would normally be designated by whatever water category it needs to protect against and where.
Where do you think you are, this website and its forums are a perfect example of a building services networking space, if your a member of the CC then there's a professional industry networking space right there. There's a huge mine of professional knowledge in there that must span hundreds if not thousands of years. Also if you have your C&G quals or were a lecturer then you should know that there is a mandatory level 3 module about career and business awareness, a critical part of that is industry networking.
Do you even know what a keyboard warrior is? Go and google that, read your comments, decide who that description better relates to and then look at the reflection in your screen.
Anyway .... I think the best thing would be for you to get back in your box and leave the forum to the better mannered pro's on here to offer their advice without elitist abuse or idiotic rhetoric.