31 .8 mm pipe, its equivalent length is 954 mm,
or 0.954 m.
Add the total equivalent lengths of all pipe
fittings to the lengths of all the pipe sections,
and enter that total length in Formula 19-1.
Total Apparent Head
The total apparent head for our purposes is
the sum of all the relevant heads for a given
piping system: static, friction, pressure, and
so on, as applicable.
Before we can find the pumping power
required, we need to determine the total ap-
parent head.
Example: Let’s say we want a deck
washdown pump as shown in Figure 19-8.
This is for a large yacht with^3 / 4 - inch (19 mm)
garden hose for the deck washdown and
(^3) / 4 - inch (19 mm) hose for most of the inter-
nal “piping.” We want a flow of 12 gpm at
20 psi (45 lpm at 140 kPa) at the nozzle outlet.
We convert psi or kPa to feet or meters of
head:
20 psi × 2. 31 = 46 .2 ft. pressure head
or
140 kPa ÷ 9. 8 = 14 .3 m pressure head
Static head is taken from the total verti-
cal lift. We include the height that the hose
nozzle will be held above the deck of about
4 feet (1.2 m), and we subtract the positive
suction head as shown to get a static head of
10 .25 feet (3.1 m).
To find friction head, we have to list all
the fittings in the line and calculate their total
equivalent length.
All are^3 / 4 - inch (19 mm) hose (except for
the fittings). Count the nozzle as a 90-degree
bend and a valve. Table 19-3 lists all the fit-
tings and provides totals.
178. 5 in. ÷ 12 in./ft. = 14 .87 ft. equivalent
length of fittings
or
452 cm ÷100 cm/m = 4 .52 m equivalent
length of fittings
Length of internal hose = 18 .25 ft. (5.56 m)
Chapter 19:Selecting and Sizing Pumps
TABLE 19-2.EQUIVALENT LENGTH OF PIPE FITTINGS
Fitting Equivalent Pipe Length
90° Elbow 30D
45° Elbow 20D
T Straight Through 16D
T Through Side 60D
Swept 90° Bend (large radius) 4–8D
Open Gate Valve or Ball Valve 9D
Open Globe Valve 25D
Full-Bore Non-Return/Check Valve 6D
Butterfly Valve 20D
Entrance 12D
Contraction d/D =^1 / 4 16D
Contraction d/D =^1 / 2 12D
Contraction d/D =^3 / 4 8D
Enlargement d/D =^1 / 4 32D
Enlargement d/D =^1 / 2 24D
Enlargement d/D =^3 / 4 8D
Vented Loop 60D
Filter/Strainer 30D
Standard Coupling 2D
NOTE: D =inside diameter of pipe or hose.
NOTE: d =inside diameter of the smaller pipe or hose that follows a reducer coupling. Thus,
Contraction d/D =the ratio of contraction in a reducer. Example: 2 inches reduced to 1 inch =
(^1) / 2 , so multiply effective length by 12D, or 12 ×ID.