Handbook of Civil Engineering Calculations

FIGURE 15. No lift; all friction head. (Peerless Pumps.)

Compute the friction loss at other flow rates in a similar manner, and plot the system-
head curve, Fig. 15. Note that if all losses in this system except the friction in the dis-
charge pipe were ignored, the total head would not change appreciably. However, for the
purposes of accuracy, all losses should always be computed.

4. Plot the low-friction, high-head system-head curve
   The system-head curve for the vertical pump installation in Fig. 16 starts at the total static
   head, 15 ft (4.6 m), and zero flow. Compute the friction head for 15,000 gal/min as follows:

ft m

Friction in 20 ft (6.1 m) of 24-in (609.6-mm) pipe 0.40 0.12

Exit loss from 24-in (609.6-mm) pipe into tank, V^2 IIg 1.60 0.49

Total friction loss 2.00 0.61

Hence, almost 90 percent of the total head of 15 + 2 = 17 ft (5.2 m) at 15,000-gal/min

(946.4-L/s) flow is static head. But neglect of the pipe friction and exit losses could cause

appreciable error during selection of a pump for the job.

5. Plot the gravity-head system-head curve
   In a system with gravity head (also called negative lift), fluid flow will continue until the
   system friction loss equals the available gravity head. In Fig. 17 the available gravity head

Copocity, L/s

Capacity, 100 gal/mm

Capacity, L/s

FIGURE 16. Mostly lift; little friction head. (Peerless Pumps.)

Head,

m

Head,

ft

Head,

m

Head,

ft

Capacity, 1000 gal/min