Welcome to CoffeeSnobs by the way [smiley=thumbsup.gif].....
It sounds suspiciously as though the Diode is either missing or shorted :o from what you describe. Sparky knows a lot more than I do about the Family and Im sure he can help you out. The Diode though, is required to provide a Half-wave Rectified Output to the Coil of the Pump. This effectively gives the pump an operating frequency of 25 Hz and as a result, full stroke of the piston inside the pump body. A 50 Hz supply only allows the pump piston to operate at half or less its designed full stroke and thus provides for a lot less output and a significantly less amount of noise too.
Once Sparky picks up on this thread he will be able to provide you with some practical advice on how to rectify the problem. Sorry I cant help you more than this..... All the best,