The second method would be to configure multiple plenums and multiple motor plates and “Stack” the two vacuum sources such that Group one pulls against the output of Group 2 which pulls against the plenum. In other words motors mounted in series.
Now a few years a go I got the bright idea of trying this Motor in Series thing thinking it would give me great benefits in obtaining higher depressions. A very wise man here on the forum, Tony told me it was not worth the effort “In a more elegant manor” but me being an experimenter and bull headed decided to try anyway. So after building a box to test 4 motors in pairs of 2 in series I learned just what Tony said. It will increase the ability to pull more depression at low flow numbers, but as flow increases the gain in depression quickly falls.
The lesson I learned is in our type of bench where you would want to flow High CFM the majority of the time, it is not cost nor power efficient. Think of it like this if you have 8 motors requiring 80 amps mains to run you will need 160 amps to run 16 in series plus twice the motor cost. Yes it can be done but I am not sure all the cost and hoops to get there is of any value on a large bench besides the PTS 8 motor bench is designed to operate at 28” and as you go up in depression the strength of the bench is VERRY Important.
Now all that said if you are building a small bench for Carting or Motorcycles and want to pull say 100” at 50CFM this is defiantly a way to solve that problem.
There is a spreadsheet on the old forum that has the data from my testing if I can find it I will post here and give an explanation. So for me I learned two things why I have two ears and one mouth and Tony was right
Rick