High-speed propellers and diagonal pumps are predominant in modern cooling water systems. The pumps are provided with adjustable impeller blades or adjustable vanes of the guide ring (prerotation guide ring). 

The both methods of control are characterized in the paper based on selected criteria and comparison with other methods. Especially thorough discussion of prerotation control is included. Results of investigations, the author's own and carried out by others, of this type of control are presented.