Quote Originally Posted by msm859 View Post
Just for the record "decreasing" pipe size will NOT increase water pressure -- if anything it will decrease the water pressure. Decreasing the pipe may increase "velocity" but you can do that at the end of the pipe.
In a pool plumbing system, decreasing pipe size most certainly will increase pressure. You are restricting flow with the same size pump. Unless your pipe has the capacity to carry much more water than the pump can deliver (not the case with pools), any change in pipe size will result in increased pressure at the pump.