Cleaner Valve

[Uncle Bobby]

Pool cleaner doesn't seem to clean as it should. In fact, since installation in 2012, it has never cleaned very well. Kreepy Krauly Platinum. Had it checked recently and it checked out fine at the pool store. There is a valve in the line that feeds the cleaner. It is about half way open. I am thinking that if I open that valve a little more, there will be more water coming in the cleaner thus increasing the suction abilty of the cleaner. That being said, the valve seems to be stuck. What is the best way to get the valve to move? It is a simple line valve with a T type handle. I have used a rubber mallet and it won't budge. I tried some huge channel locks but I didn't want to use too much force. Any ideas? Thanks