Hi
The Grunfoss 1550 looks to be a central heating circulating pump an driven by an induction motor. Induction motors rely on the rotor rotating in sync with a field generated by the stator which is in part determined by the mains frequency. As such they are intended to run at a fixed speed and not as a variable speed unit, however the speed of this type of motor can be varied by the use of a variable frequency drive or VFD but these are usually quite expensive.
The standard dimmers as supplied by the local hardware shops are not VFD but switch the supply voltage at varying points in the cycle to effectively vary the power available to the load. Mains powered motors such as those used in sowing machines, hand drills etc are not synchronous (induction) motors and can be used with this type of dimmer, power regulation, unit. However I think you will find that using a standard dimmer with and induction motor wont give the results you want.
I stand to be corrected by the more knowledgeable.
Hope this helps.
Martin
PS KWIL's suggestion is far more practical and will let you adjust the flow easily
Edited By Martin W on 11/11/2013 16:15:08
Edited By Martin W on 11/11/2013 16:15:36