We give due importance to outlet velocity while selecting the control valve due to noise and probability of pipe vibration. While at the same time, we hardly see this angle in sizing calculation of orifice beta ratio. Please suggest the reason behind it

 

Piece of Cake!

Good orifice metering based on installations that are hydraulically similar, ie. same reynolds number range, and for orifices that have beta rations 0.3-0.6 or so. In effect this places limits on the inlet, throat and outlet velocities that are well within "safe fluid velocities." These velocities are well below those associated with valves or high pressure drop applications.

Having said that, for square-edge orifices, edge sharpness must till be checked routinely, to avoid loss of accuracy.