Borehole pump speed control?

I have a single phase 240v 50hz borehole pump that works by vibrating a membrane at the supply frequency. It is a bit too powerful so I am reducing the supply voltage with a Variac but i worry that the subsequent increase in current might damage the pump. What other ways are there to control the pump powerBorehole pump speed control?
One method would be to use a single-phase variable frequency drive (VFD). It decreases the voltage in proportion to the decrease in frequency, thereby operating the motor at the correct voltage for the reduced frequency. A VFD can be expensive, however.





Is there any way to mechanically modify the vibrator so that it doesn't vibrate as hard? Such as reduce the size of an actuating cam, if it has one? Or is this a solenoid that vibrates the membrane, not a motor?





You said that current increases with a decrease in voltage. That is indicative of a motor's response. If it is a solenoid, I would expect the current to decrease, not increase, when the applied voltage is reduced, so a voltage reduction should not be harmful. Have you measured the current?





In either case, a VFD will work with a solenoid or with a motor.Borehole pump speed control?
Could using a smaller pipe help?....................a larger pipe then?............................ Oh yes I see now ..............................
I'd tell you, but that would be like doing your homework for you.





All I will tell you, is the answer is 42.
Is it bigger though really?