Dear Mohd, You have received ...

Dear Mohd,

You have received very good comments of this professionals!

I would like to add that the velocity is a crucial parameter to determine the internal diameter or viceversa, on the other hand the material and pressures are other important variables to solve your system.

The instalation and use of the water are other paramters to have into account.
As an example, if you have short distances, and must pump between high differential pressure (example: inlet pump and outlet pump pressure), as  example boilers, you could use 4,5 m/s, and maybe more... but if you must pump water in a zero slope line for several kilometers, you will want the less possible velocity that gives you less lost in the water system, then you could think in 0,6 to 1 m/s...

Regards,

Orlando D. Gutiérrez Coronado