Hello MMD'ers,  John Runge has problems finding the right speed of the
wind machine for his Decap dance organ.  When replacing the AC motor
most important to know is what kind of motor was installed originally.
The synchronous speed of a asynchronous motor is expressed in a simple
formula:

  N = Frequency x 60 / Number of pairs of poles,
      expressed in revolutions per minute.

So the synchronous speed (under no-load conditions) of a 2-pole motor
applied with 50 Hz is 3000 revolutions per minute, a 4-pole motor will
run at 1500 rpm, etc.  With a mains frequency of 60 Hz, the speed will
increase with the ration 60/50 = 12%.

For calculating the real speed under nominal load you have to extract
the so-called slip of the motor, being about 5 to 10 % of the
synchronous speed.

The motor nameplate (as we call it here in the Netherlands) will reveal
what kind of motor you are dealing with.  Chances are that your Decap
was installed with a 4-pole 50 Hz motor.

I also would suggest to connect two U-shaped hoses, half-filled with
water, somewhere on the wind chest and the bellows for suction, to
measure the actual pressure and suction applied to the Decap.

Greetings from the Netherlands,

Willy van der Reijden