Hi All

On the subject of vacuum cleaners, you have to be a little careful.
I'd forget anything domestic for a start, they won't take the strain
for long. Look at Numatic or Nilfisk.

There are two types of motor used in commercial vacuums. Vacs designed
for dry use have Direct Cooled motors - that is, the air they suck
passes over the armature etc to cool it down. Stop the airflow for any
length of time and the motor will overheat - no good for vacuum tables.

Vacs designed for wet or wet/dry use have By Pass motors. The air they
suck is diverted sideways away from the amrature (wet air on electrics
not being a good idea) and they have a separate fan on the back for
cooling purposes. They will continue to operate without any airflow,
so won't burn out on a vacuum table.

By pass motors come in two types - peripheral discharge and tangencial
discharge. By discharge I mean how the air leaves the motor.
Peripheral discharge have slots around the casing, tangential have a
tube.

Two tangential by pass motors can be connected in series (inlet of one
connected to out let of the other) to increase vacuum. Most twin vac
carpet extraction machines work like this.

Connecting in parrallel, as in most twin motor vacs only increases
airflow, suction remains the same.

Hope that helps

Dave