What is the exact and precise criteria for mainline looping head loss calculation?

Normally we use hazen william equation to find out losses in mainline while designing any drip or sprinkler irrigation system, however, if we make it in loop then we divide total flow into half and take half legth of total pipe. as flowing water will be divided into2 parts. Half on1 side and other on other side.

1- the diameter

2- the inner surface roughness which lead to the friction losses

3- the length of the line

4- the velocity of water flow

losses divided to mnimum and major losses

minimum losses such as (in , out , loop ,............. )

but major losses calculated by darcy , scobby , hazen william formula

so that found program designed to calculate thes on excle

i'm doing excel programe about losses calculate in athird year in my college

use hazen wiliams formula for calculating the headloss in the mainline , if its pvc, consider roughness calculation as 150, velocity for pipesizing should not be greater than 5fps or 1.5mps maximum headloss should not be greater than 0.35 f / 100 f for safe irrigation system, for looping you must divide flowrate by 2 and also the length of the pipe.

If you want to calculate the head loss in loop system you have2 ways *hardy cross equation wich assumes the amount and the direction of flow either its clock wise or counter clock eise and by this way you will have alot of assumbtions and after you calculate all if them you can take the highest head loss to calculate your pump head The other way is to assume that the most of the flow is going through one branch and you should take the longest path by other word the critical path