Can any one guide me how to calculate Horizontal saftey Valve Reaction Force in Boiler Steam Line Asper Mandetory AppendixII you can only calculate Vertical force of saftey relief valve not horizontal.

If I look at API its says 2/3 of Horizontal force is vertical

I have received V-hr=20440N V-vertical=3755N

Can any one Please tell me how to calculate horizontal force .