Laminar flow takes place with liquids operating at low Reynolds numbers. This occurs with liquids that are viscous working at low velocities. Laminar flow in gases and vapors very seldom will be experienced in process plants.
8. The control valve size is essentially always equal to the line size. Is this correct? NO. The control valve does not need to be of the same size as the pipe.
Don’t assume a 4” valve will handle the flow in a 4” line. The flow path is the critical factor and shape of the flow passage in the valve can be a problem. Look at the pressure through the valve and if the
valve creates a pressure drop, then a slightly larger valve maybe needed. Always calculate the flow coefficient.
Even fora given size of valve, there is no industry-wide standard pressure for valve sizes no two manufacturers design a 4"
valve the same way, and different designs have different pressure considerations. Contrary
to conventional wisdom, it is better to make an error in under sizing a control valve than to oversize it.
Share with your friends: 
