Motor power control?

As I mentioned before, even a family use vacuum cleaner has excessive capability if it is utilized in the vacuum system of our new laboratory, because the dust indicator shows fully occupied mark immediately after setting in the air duct line.
In short the power of the electric motor device is yielded easily with direct connection and this would be destroyed sooner or later if continued being used under overloaded situation.
In another words, the conduit resistance is so strong as to make the device scream.
The destruction of the vacuum motor, family use vacuum cleaner here, does not triggered by the moisture included in the suction air but because of continuous using under the overloaded condition.
Because of those reasons I feel the critical necessity to release the motor from overloading circumstances.
I imagined two ways, one is making some bypass air ways to release the yielded vacuum pressure and another one is reduce the power of the motor by let the activating voltage by some way, for example setting a step-down transformer like voltage linear convertor? Anyway output matching to the load is indispensable factor here also.
The correct selection must be the latter, reduction of original in-put energy to the motor to the level that the dust indicator shows no sign, no?