Very recently, Big Clive did a video on a piezoelectric air pump:
I decided to get a 120V version for a simple project I wanted to play around with (atmospheric CO2 sensor) and I decided to open up the plug to analyze the circuit inside. The circuit is basically the same as for the 240V version:
* It has two 2k resistors in series instead of three 8.2k.
* The capacitor is the same but the inductor is 1.4mH.
* The silly 1M across the first resistor is there, along with another 1M across the pump.
* The pump itself measures about 63nF.
Not sure the exact purpose of the inductor. I was expecting it to form a resonant circuit with the pump but probing with a HVP70 probe across the inductor showed almost no voltage. Something interesting to note is that with the probe across the pump, the voltage slightly increases when the output is blocked.