Q. If you split flow streams in an e-coat paint recirculation line, what is the best method for manipulating flow rates that would minimize excessive shear on the paint? Would it be better to vary the pipe diameter or throttle with a butterfly valve?—M.A.
A. Fluid shearing refers to the development of external forces that strain or disrupt laminar flow. Thus, the pipe diameter increase will produce less shearing in the paint than installing a butterfly valve and throttling to decrease flow. Additionally, valves introduce significantly more pressure drop in the system than the roughness of the piping and require more energy to accomplish.