Shop Vacuum Question

[Carlton Duke]

A debate has started at one of our local woodworking stores which someone may be able to help with. Ques: when the intake of a shop vacuum(or any vacuum for that matter) becomes stopped up and the motor begins a much higher pitched sound, what has happened? Is the motor all of a sudden under a much higher load which causes the change or is it because the fan is all of a sudden starved for air and the motor is under no load at all and races to a much higher RPM which causes the higher pitch? In either case is the motor likely to fail/burn up/etc if nothing is done to unstop the intake? Thanks for your inputs- cduke

[David]

Without air moving through the unit, the motor will overheat very quickly.

Dave

Carlt> A debate has started at one of our local woodworking stores which

[kkfitzge]

The motor is speeding up because there is no load on it. Whether or not this is harmful depends on the design of the vac: Cheap vacs use the exhaust air to cool the motor, and will overheat when the intake is blocked. Better vacs have a bypass fan to cool the motor independently.

[Robert Bonomi]

The "mechanics" of what is going on depends _greatly_ on the design of the particular unit.

Some types speed up because they do -not- have as much of a load of air to push against. It's not "no load at all", but a 'lower load'.

Other types have to 'work harder', because of the increased partial vacuum they're working against.

In _either_ situation, the unit *IS* likely to fail/burn up/etc. if left in that condition for an extended period. Almost all units use the airflow to cool the motor. Stop the airflow, and the motor *will* overheat. Which leads to disastrous results.

[bridger]

the motor is under no load. the RPMs go up and the cooling airflow goes away. the motor will get hot and likely overheat if left running.