I added a new Hayward pump and sand filter and know the water returning to the pool has alot of air in it the return line is making a chugging sound. When I look in the top of the pump (were the skimmer is the water is low) and the hose going from the pump to the sand filter is not full. I have found a fix for this by partial closing the valve on my return line. This also shows a higher pressure on the gauge from 12 psi with valve open to about 18-20 psi partial closed. Does anybody know why it is doing this? Do I need to have two suction inlets?