I don't know where else to ask this, and it seems like this group would probably have some expertise in this area.
I want to use an old shop-vac as a heavy-duty exhaust fan. I have an application where I need to pull hot air out of an equipment area. I made a serious mistake and built 3" flexiduct into the walls to the exhaust fan area. The 3" flexi is a very thin straw, and normal fans can't suck enough air through them. (I've tried 5 different fans of varying types and they can't hack it.) I can't change the flexi without ripping out several walls -- not gonna happen. Hence the shop-vac.
The shop-vac can pull LOTS of air through the 3" duct -- TOO much. I need to reduce the amount of air it pulls. I could just introduce a "leak" in the duct but that seems like a very bad solution.
I'd much rather slow the fan down to just the right level I need, which will also reduce the noise level.
Is a router speed control like this one OK to use on the kinds of motors used in shop-vacs?
BTW the vac will run for 2-4 hours at a time. That's probably more than the recommended duty cycle for a shop-vac but hopefully it will be OK. Especially if I slow it down.
Thanks, Gary