The pump must be set at a speed that produces 17 to 25 psi at the water valve gauge(s) and cleans the pool. The cleaning system relies on a specific GPM per circuit and a pressure adequate to clean and move the debris down and into the main drain.  This also requires the debris receiving drain is flowing a minimum of 35 plus gallons per minute. On a normal non-Venturi skimmer, the skimmer must be set no more than 1/3 the way open to obtain proper flow at the main drain.