I am new to pools so I am just learning. I have a 3 way valve before the pump (suction side) adjusting the flow between the skimmer and vacuum. I had air coming in when I added any flow to the vacuum. As a result, the vacuum barely moved. I also had slow flow through the skimmer. I couldn't find a leak in the vacuum line and was getting frustrated.
Then I thought that it might be the valve. So I cleaned and lubed the o-rings and no more leak! The amount of suction increased dramatically. I was able to cut the watts on the pump in half and the vacuum moves faster than it was with more flow through the skimmer.
What a difference!