Just finished building a heavy duty vacuum for a buddy

I built a similar vacuum setup a few years back when I got sick of renting those underpowered gas units from the local supply house. I used a 14hp Kohler engine and a custom 18-inch impeller. One thing I learned the hard way is that the interior welds on the housing need to be ground completley smooth. If there's even a tiny burr or a bead that's too high, that old damp cellulose or wet fiberglass starts snagging and builds up a clog in seconds. I ended up switching to a 6-inch flex hose for the intake instead of the standard 4-inch beacuse the suction was actualy collapsing the cheaper ribbed tubing. You might want to keep an eye on your discharge side too; if you're blowing into those big collection bags, the back pressure can get intense enought to stress your seals more than the suction side does. I had to go back and add a double-bolt flange on my outlet because the vibration kept rattling the primary clamps loose during six-hour attic pulls.

I’ve gone the custom route before, but honestly, I ended up pivoting back to modified commercial units becasue of the weight distribution. When you overbuild with that thick steel plating, it’s a beast for the crew to move, even on a rolling frame. I found that using a lighter gauge steel reinforced with external ribs gave me the structural integrity I needed without making the rig a nightmare to get off the truck on uneven gravel driveways.

One thing I’d watch closely tomorrow is the heat buildup near that top-mounted tank. On the 12hp Honda units I’ve worked on, the vibration and heat soak can sometimes lead to vapor lock if the airflow around the engine isn't perfect. I eventually started mounting my tanks off-side or using a remote fuel setup. If you notice it sputtering after an hour of heavy suction, check your fuel lines first. It’s usally not the welds failing, but the engine getting choked out by the heat radiating off the housing.

Watch your engine cooling with that top-mounted tank. I did a similar build and found that the radiant heat off the housing during an eight-hour pull was vapor locking my fuel line. I ended up having to fab a small heat shield out of some scrap aluminum to keep the tank from getting cooking-hot. Also, keep a heavy duty rubber mallet handy for the first few hours. Even with smooth welds, you'll get some static buildup with dry fiberglass that likes to bridge right at the intake transition. A couple of solid whacks to the pipe keeps the flow moving when you hear the pitch of engine tone change.

That suction sounds killer, but you'd better check your ear pro situation. I built a beastly rig last summer and didn't realize how loud that thick steel housing woud ring once the fiberglass starts hitting it like sandpaper. It's way noisier than the plastic commercial units. Are you guys running a muffler on the exhaust or just gonna' wing it with some heavy-duty muffs? I'd also keep an eye on the impeller balance after the first few hours—if a chunk of wood or some old debris gets sucked up, it'll vibrate those new welds to death if it's not perfectly centered.

If you’re pulling old fiberglass, check your impeller blades for abrasion early on. I ran a custom build with an 18-inch AR400 steel fan, and even that took a beating from the grit. If you didn't go with abrasion-resistant plate, keep a spare assembly in the truck. Also, what’s your static pressure looking like? If you’re hitting over 25 inches of water column, those standard 6-inch clamps are going to fail. I’d swap them out for some heavy-duty T-bolt clamps now before you're halfway trough a 2,000 square foot blow-out and lose a hose connection.