Firsly, you need to know how to use the K value. It is the same as mechanical engineers use as Cv of valves.
Cv=gpm/√psi K=gpm/√psi
gpm=Cv*√psi gpm=Cv*√psi
psi=(gpm/Cv) psi=(gpm/Cv)
Second, You have to use the Hanzen-Willians pipe friction losses.
4.52 * Q1.85
p=________________
C1.85 * d1.87
where: P= Loss in psi per ft.
Q=gpm
C=Friction loss coefficient (c=120)
d=Inside diameter.
Now, you can look at pages from 13-247 to 249 of NFPA 13.
Rdgs,
rewatson