Staged Vacuum Motors?

[DaveMcLain]

The other day I was discussing flow bench designs with a friend and wondering about how a bench would work with more than one stage of motors. Right now most flow benches work with a "bank" of multiple vacuum motors in parallel to produce the depression. How would the same motors perform if they were built into a bench design where instead of parallel they would be in series? Would the effective pressure that they could develop essentially double or does it not work that way?

[Tony]

Connecting motors in (flow) series will certainly generate a higher developed pressure, but will do almost nothing to increase the available flow.

What we are trying to do in a flow bench is test various components usually at a known fixed test pressure, where the motors operate within a fairly narrow pressure operating range, but a very wide possible flow range, depending on what is being tested.

The biggest problem is almost always reaching the highest achievable amount of airflow, with the lowest possible electrical power draw.
If your home power is limited to twenty amps because that is the fuse or circuit breaker rating, we try to achieve the most airflow from that we can.

The trick is to select vacuum motors that operate at their highest efficiency around the required normal bench operating pressure, then fit enough of those same motors according to the available power to run them.