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

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

Dave

Carlton Duke wrote:
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

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.

In article ,
Carlton Duke wrote:
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

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.

On Sun, 20 Mar 2005 19:58:45 -0500, Carlton Duke
wrote:

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



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.