Page 414 - Civil Engineering Formulas

340 CHAPTER TWELVE

Friction Head. The head of water that must be supplied to overcome the
frictional loss caused by the flow of fluid through the piping system is the friction
head. The frictional head loss in the suction (h ) and discharge (h ) piping
fs
fd
system may be computed with the Darcy-Weisbach or Hazen-Williams
equations, discussed earlier in this chapter.
Velocity Head. The velocity head is the kinetic energy contained in the liquid
being pumped at any point in the system and is given by
V 2
Velocity head (12.144)
2g

where V velocity of fluid, m(ft)
2
2
g acceleration due to gravity 9.81 m/s (32.2 ft/s )
In determining the head at any point in a piping system, the velocity head must
be added to the gage reading.
Minor Head Loss. The head of water that must be supplied to overcome the
loss of head through fittings and valves is the minor head loss. Minor losses in
the suction (h ) and discharge (h ) piping system are usually estimated as
ms md
fractions of the velocity head by using the following expression:
V 2
h m K (12.145)
2g
where h minor head loss, m (ft)
m
K head loss coefficient
Typical values of K for various pipeline fittings and appurtenances are pre-
sented in standard textbooks and reference works on hydraulics.
Total Dynamic Head. The total dynamic head H is the head against which the
t
pump must work when water or wastewater is being pumped. The total dynamic
head on a pump, commonly abbreviated TDH, can be determined by considering
the static suction and discharge heads, the frictional head losses, the velocity
heads, and the minor head losses. The expression for determining the total
dynamic head on a pump is given in Eq. (12.146):

2 2
V d V s
H t H D H S (12.146)
2g 2g
(12.147)
H D h d h fd
h md
2
H S h s h fs
h ms V s (12.148)
2g