Single Phase Motors
The speed control of universal motor used for sewing machines is by

Centrifugal mechanism
Varying the resistance
Friction
Tapping the field

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Single Phase Motors
If the centrifugal switch of a two-value capacitor motor using two capacitors fails to open then

current drawn by the motor will be excessively high
electrolytic capacitor will, in all probability, suffer break down
motor will not come up to speed
motor will not carry the load

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