Any one out there who could help me? Swimming pool pump works fine, but when hoover is connected there´s no power and the pump makes a grating noise. When hoover disconnected, and normal setting for pool filter, all works fine. Any ideas?

It sounds like the pump is cavitating due to air in the pipework.

Prime the vacuum hose with water before plugging into the vacuum port. Leave the skimmer OPEN, MPV to WASTE, vacuum port to CLOSED and then turn on pump. Crack open the vacuum port slowly until the remaining air is pulled through, slowly open port fully. Close the skimmer and you're good to go.

Or your vacuum hose is blocked!

Thanks for the help. I´ll try that,