cfm and water lift

My first 3 portables were in series.. The last one was in parallel.. No matter which one you run i would still keep your hose runs as short as possible..

All I can talk about is my personal experience.

I have a Diamonback with dual 3 stage-vacs.  The came in a series with a 1.5" port.  I've used this machine like this for 5 years or so. 

After getting advice from Friendly, I decided to switch them over to parallel.  Not only that, I opened up the 1.5" to a full 2", and put a cool cuff male starter cuff in the hole instead of a 2" barb, which actually isn't even 2".  All I can say is that the vacs are screaming now instead of sufficating in each other.  It doesn't even sound like the same machine.  The vac power seems significantly better than before. 

I can switch it back to series pretty easily, but I don't think I ever will.

I though about adding a 3rd 3 stager.  Steambrite sells a vacuum booster than takes the place of your 6" recovery tank lid.  They also sell a dryer plug adapter that will allow you to plug in up to 4-15amp plugs.  I have decided not to do this at the moment, mainly because I intend on pursuing more commercial accounts, which would render that dryer adapter useless.  It may be a good option to have that booster, just in case one of your 3 stagers gives out at a job.

By the way, if you are not running one of your vacs configured in parallel, I think you need to cover the exhaust hole of the vac not in use, otherwise air will be pulling through that vac.