pump? A swing check valve is used on the pump suction line and a gate valve on the dis-
charge line.
Calculation Procedure:
- Sketch the possible piping arrangements
Figure 4 shows the six possible piping arrangements for the stated conditions of the in-
stallation. Label the total static head, i.e., the vertical distance from the surface of the
source of the liquid supply to the free surface of the liquid in the discharge receiver, or to
the point of free discharge from the discharge pipe. When both the suction and discharge
surfaces are open to the atmosphere, the total static head equals the vertical difference in
elevation. Use the free-surface elevations that cause the maximum suction lift and dis-
charge head, i.e., the lowest possible level in the supply tank and the highest possible lev-
el in the discharge tank or pipe. When the supply source is below the pump centerline, the
vertical distance is called the static suction lift; with the supply above the pump center-
line, the vertical distance is called static suction head. With variable static suction head,
use the lowest liquid level in the supply tank when computing total static head. Label the
diagrams as shown in Fig. 4. - Compute the total static head on the pump
The total static head Hts ft = static suction lift, hsi ft + static discharge head hsd ft, where
the pump has a suction lift, s in Fig. 40, b, and c. In these installations, Hts= 10 + 100 =
110 ft (33.5 m). Note that the static discharge head is computed between the pump center-
line and the water level with an underwater discharge. Fig. 4a; to the pipe outlet with a
free discharge, Fig. 46; and to the maximum water level in the discharge tank, Fig. 4c.
When a pump is discharging into a closed compression tank, the total discharge head
equals the static discharge head plus the head equivalent, ft of liquid, of the internal pres-
sure in the tank, or 2.31 x tank pressure, lb/in^2.
Where the pump has a static suction head, as in Fig. 4d, e, and/ the total static head
Ht 3
ft
= h*d ~
static
suction head hsh ft. In these installations, Ht = 100 - 15 = 85 ft
(25.9 m).
The total static head, as computed above, refers to the head on the pump without liquid
flow. To determine the total head on the pump, the friction losses in the piping system
during liquid flow must be also determined. - Compute the piping friction losses
Mark the length of each piece of straight pipe on the piping drawing. Thus, in Fig. Wa,
the total length of straight pipe L,ft = 8+10 + 5 + 102 + 5 = 130ft (39.6 m), if we start at
the suction tank and add each length until the discharge tank is reached. To the total
length of straight pipe must be added the equivalent length of the pipe fittings. In Fig. 1Oa
there are four long-radius elbows, one swing check valve, and one globe valve. In addi-
tion, there is a minor head loss at the pipe inlet and at the pipe outlet.
The equivalent length of one 8-in (203.2-mm) long-radius elbow is 14 ft (4.3 m) of
pipe, from Table 3. Since the pipe contains four elbows, the total equivalent length =
4(14) = 56 ft (17.1 m) of straight pipe. The open gate valve has an equivalent resistance of
4.5 ft (1.4 m); and the open swing check valve has an equivalent resistance of 53 ft
(16.2m).
The entrance loss he ft, assuming a basket-type strainer is used at the suction-pipe in-
let, is he ft = Kv^2 /2g, where K = a constant from Fig. 5',V = liquid velocity, ft/s; g = 32.2
ft/s
2
(980.67 cm/s
2
). The exit loss occurs when the liquid passes through a sudden en-
largement, as from a pipe to a tank. Where the area of the tank is large, causing a final ve-
locity that is zero, hex - v
2
/2g.