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I have a PVC dust collection system comprised of 3" piping through my shop. It works pretty well, except I would benefit from a bit more airflow. I have two shop vacs, one of which is pretty much dedicated to this task, the other is just a miscellaneous use one.

If I hook them up to the same outlet on the pipe, can I increase the airflow through the pipe? The pipe will support it (by my calculations) but I am not sure if it is effective by having the two vacs.

I also don't want to stress the motors or cause the fuse to blow continuously, so this is not a 'try it and see' scenario.

Thanks!

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    Note that you may need to put them on separate circuits if they pull more than 80% of the rated amps of your circuit, and that the shop vacs will also be pulling against each other, not just the open end of the pipe. If the airway becomes clogged, it will be extra hard on the vacuums. If you are looking for more airflow, you should look at a dust collector and larger pipe, and/or redesigning how your pipe is laid out (shorter runs, blast gates, no 90 degree bends, etc.)
    – rob ♦
    Commented Mar 30, 2017 at 17:20
  • Building your own blower for a dust collector isn't that hard once you find a suitably rated motor.
    – ratchet freak
    Commented Mar 31, 2017 at 10:20
  • I already have very gradual turns: 22.5 -> 22.5 -> 22.5 -> 22.5 as the majority. Everything is split using wye joints accordingly, and I have blast gates at every tool/zone.
    – Barry Chapman
    Commented Apr 26, 2017 at 3:20
  • I think the general concept of setting this up in parallel with a cyclone canister as the pull spot for two vacuums make sense but the question that nags at me is wouldn't the two vacuums be trying to pull air from each other as well as the cyclone canister? In the envisioned canister setup do you have the Y right after the canister attachment point or are you creating two outs on the canister? Did the OP end up setting this system up, how did it work?
    – Fresh Codemonger
    Commented Jun 27, 2018 at 19:05
  • @rob - I did end up going with your suggestion to have them on separate circuits. The 6.5 HP (cough bs cough) peaked at around 13amps in normal operation. I put each device on a 15A circuit, which does trip if one of the vacs becomes blocked. This was an acceptable failsafe for this! However, once one of the vacs stopped working, I had a suspicion that suction would start to come through the non functioning device. Anyone seen any kind of one-way valves or DIY ways to accomplish that? Just a thought!
    – Barry Chapman
    Commented Jul 2, 2018 at 3:00

3 Answers 3

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This could work, but you would want them setup to run in parallel, and not in series I would think. For example at the end of your ductwork, you have a Y that splits right into the two vacuums. My guess is the stronger vacuum will end up with the majority of your dust.

However if you set this up with a cyclone, you can still centralize all of the dust collection into a single bin, and still utilize the suction of two vacuums.

The biggest issue I can see happening is if you ever get a blockage, or accidentally close all of your gates, the vacuums will in essence be fighting each other in the closed system, and the weaker one will blow.

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    +1 to the cyclone/ big garbage can. It's amazing how much that benefits your shop vac.
    – Aloysius Defenestrate
    Commented Apr 2, 2017 at 16:07
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In series works for me. Parallel with a "Y" degraded the suction. I'm running (2) 6.5 hp. It was only practical for long hose runs.

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  • Hi, welcome to SE. Could you edit your Answer to provide more details on how you set this up for the help of future searchers? Photos would help if you can manage them. Think more "Here's how I set up shop vacs in series..."
    – Graphus
    Commented Jun 16, 2019 at 7:17
  • I am not sure how the parallel degraded the suction. Static pressure, I believe - would operate kind of like a speaker circuit in a way [with regards to ohms]. With the devices in parallel, i would have thought it would suck at the same rate, but move more air. This may be a moot point given that the tube sizes are variable. But two 8ohm speakers wired in parallel would yield 4ohms of resistance (effectively halving it). In series, would double the resistance, making it 16ohms - the same thing would happen here, right? correct me if i am wrong.
    – Barry Chapman
    Commented Jun 28, 2019 at 19:15
  • My point is - doubling the resistance would murder the motors, since they would have to work a lot harder. The parallel setup would, in effect, half the amount of work required by the motors.
    – Barry Chapman
    Commented Jun 28, 2019 at 19:16
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Instead of running them in parallel (i.e. with a "Y-joint") I would run them in series. Plug the intake of the first shop vac into the exhaust of the second, then plug the intake of the second into your dust collection system. This would definitely have more air flow and pull a higher vacuum for pulling clogs through. Also with two filters inline it would also filter better. Most of the debris would be in the second vacuum, so you would only have to empty (and change the filters on) one of them most of the time.

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  • This is going to burn out the motor of one or both of the shop vacs by making them run much faster than their motors are rated for.
    – SaSSafraS1232
    Commented Jan 11, 2018 at 22:53
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    Shop vac's don't typically spit some of the debris out that they have sucked up. They wouldn't sell very well. Imagine dear old Beatrice gets a shop vac to clear ashes in her fireplace, and 20% of that ash scoots out the outlet of the shop vac, while the other 80% is kept inside. We would have a very unhappy Beatrice. What would happen in reality, is that the vac at the end of the chain would be pulling on the outlet of shopvac '1', causing it to spin like an aircraft jet engine. Since shop vacs are not built for jet propulsion, we would be out a shop vac.
    – Barry Chapman
    Commented Jul 2, 2018 at 3:07

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