Handbook of Civil Engineering Calculations

ft m

At 150 gal/min (9.5 L/s), friction loss in 200 ft (60.9 m) of 4-in (102-mm) pipe 5 1.52

At 150 gal/min (9.5 L/s), friction loss in 200 ft (60.9 m) of 3-in (76.2-mm) pipe 19 5.79

Total static head for 3- (76.2-) and 4-in (102-mm) pipes 10 3.05

Total head at 150-gal/min (9.5-L/s) flow 34 10.36

Compute the total head at other flow rates, and then plot the system-head curve as

shown in Fig. 18.

7. Plot the system-head curve for two discharge heads
   Figure 19 shows a typical pumping system having two different discharge heads. Plot
   separate system-head curves when the discharge heads are different. Add the flow rates
   for the two pipes at the same head to find points on the combined system-head curve, Fig.


8. Thus,

ft m

At 550 gal/min (34.7 L/s), friction loss in 1000 ft (305 m) of
8-in (203.2-mm) pipe 10 3.05
At 1150 gal/min (72.6 L/s) friction 38 11.6
At 1150 gal/min (72.6 L/s), friction + lift in pipe 1 88 26.8
At 550 gal/min (34.7 L/s), friction + lift in pipe 2 88 26.8

The flow rate for the combined system at a head of 88 ft (26.8 m) is 1150 + 550 =
1700 gal/min (107.3 L/s). To produce a flow of 1700 gal/min (107.3 L/s) through this sys-
tem, a pump capable of developing an 88-ft (26.8-m) head is required.

8. Plot the system-head curve for diverted flow
   To analyze a system with diverted flow, assume that a constant quantity of liquid is
   tapped off at the intermediate point. Plot the friction loss vs. flow rate in the normal
   manner for pipe 1, Fig. 20. Move the curve for pipe 3 to the right at zero head by an
   amount equal to Q 2 , since this represents the quantity passing through pipes 1 and 2 but

Capacity, L/s

FIGURE 19. System with two different discharge heads. (Peerless Pumps.)

Capacity, 100 gal/min

Combined

system

curve

Head,m Head,ft