MIL-HDBK-1005/9A
c) Head Loss Determination. Calculate the head loss
across the pier riser assembly (Hr), the lateral (Hl), and the
lateral-main intersection (Hlm) based on maximum Qlateral flow rate
and design viscosity using Equations 9, 10, and 11,
respectively. See Figure 11 for design nomenclature.
Hr = [K(Qlateral/D2)2/2g][0.1669]
EQUATION (IP):
(9)
or
Hr = [K(Qlateral/D2)2/2g][1586.7]
EQUATION (SI):
where
Hr
=
head loss across pier riser assembly,
ft(kPa)
D
=
lateral diameter, in. (mm)
Qlateral
=
as per Equation 7, gpm(L/s)
32.2 fps2 (9.81 m/s2)
g
=
K
=
head loss coefficients for pier riser
assembly. See Figure 8 for description of
fittings in pier riser assembly.
Hl = [f(L/D)(Qlateral/ D2)2] /g
EQUATION (IP):
(10)
or
Hl = [f(L/D)(Qlateral/D2)2/g] [79,217]
EQUATION (SI):
where
Hl
= head loss through lateral from pier riser to
lateral/main intersection, ft (kPa)
L
= length of lateral from pier riser to main,
ft (m)
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