there is no switching valve, the return goes from the filter strait into the shasta cleaner " the floor cleaner " its 20 year old. when ever the gears inside switch to a diffrent set of pop ups the pressure drops to 22psi then goes right back up to 30. i believe the restriction is in the floor cleaner control head. also some pop ups where replaced, could the outlet holes on the floor pop ups be to small causing the restriction?