Puzzzled about PVC flow

[cleancloths]

What comes into play is that flow is a function of linear velocity in the pipe and for the purposes of noise and physical damage (at joints and bends) you don't want to exceed rated velocity in a piping system.

[catnip]

Check this post on the Hayward site. It deals with the hydraulics of sizing pipes, pumps and filters in a very easy-to-understand manner. You will see that the maximum standard flow rate for 2" PVC pipe is 105 GPM on the pressure side and 85 GPM on the suction side.
http://www.haywardnet.com/pdfs/Pump_filter_sizing.pdf

Depending on the total dynamic head and the pump curve of your 2 HP pump you could easily be exceeding the 85 GPM limit on the suction side. To be safe you could use 2.5" or better yet 3" PVC from the junction of your side and bottom drain lines to the pump. You should also look at your pressure side pipe sizing to be sure you are OK there as well. I would "guess" that you would need at least 2.5" PVC from the pump through the filter and out to any T's that split to your returns.