As a casual woodworker I’ve been using shop vacs for my dust collection duties rather than go to the expense and installation of a central dust collection unit. I have a bunch of Ridgid shop vacs that I bought when on sale at Home Depot. (This year’s Black Friday deal was a 5 HP unit for $29.)
This plan has had a problem or two. The vacs on sale, though powerful enough to handle my planer and jointer, come with an undersized flexible hose - 1 7/8". This would probably clog when used with a machine that makes a lot of chips. A proper 2 1/2" hose assembly is about $20.
The other problem is that some recent Ridgid vacs have been using a proprietary inlet instead of the standard 2 1/4" tapered hole. So standard adapters or hoses from other brands are too small. The inlet on these bigger Ridgids is a non-tapered 2 5/8" hole (give or take a few thousandths). Keep in mind that different Ridgids have different inlet sizes, so check yours.
I had an idea to use bulk 2 1/2" dust collecting hose like Penn State Industries sells ( http://www.pennstateind.com/store/D2515.html
), cut pieces to proper length and connect the vacs to my machines. The problem was getting the hose to fit the Ridgid vac.
I wandered the plumbing and electrical aisles of the local big-box home stores and couldn’t find any fittings that would be a snug fit in that pesky Ridgid inlet. The closest I could find would be a 2" PVC pipe coupling, but it was a few thousandths too big.
Finally, I was in an auto parts store and checked out exhaust pipe adapters. I took a couple home with me and was happy to find that one fit. It’s a 2 1/4" I.D. to 2 1/2" I.D. adapter and slips right into the shop vac with almost no clearance. The small end is the right size for the flex hose, too. Since they are thin walled (as compared to PVC) they don’t restrict flow. And they only cost about $3!
The one in the picture is made by ROL Exhaust but I’m sure there are a lot of other manufacturers who make an adapter this size. Hope this helps somebody who was dealing with the same predicament!