I am replumbing my AGP and my setup includes three 3-way pentair valves. The valves are designed to take 1 1/2" pipe on the inside flange or 2" pipe on the outside flange. My plan is to connect to/between all valves using 2" elbows and tees (slip/thread type) and then transition down to 1 1/2 for the pipe runs to/from the equipment and pool (using 2" male thread/1 1/2" female slip fitting). My reason is for ease of repair (threaded fittings will save the valves if repair is needed) and I figure the reduced drag through the elbows is a good thing too. The fittings on the filter and pump are 1 1/2" so everything else (pump to filter, etc) will be 1 1/2" . The only 2" pieces will be the elbows and Tees that connect to valves.
Is there a down side to this plan? My fear is that the mixing of pipe sizes will cause it to sing, scream or moan. Any need for concern? My pump is a 1.5 hp Matrix Powerflo 2-speed, always run on high.