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Fluid Energy Loss in Fittings and Valves Formula, Calculator and Tables

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Fluid Energy Loss in Fittings and Valves Formula, Calculator and Tables.

There are two standard ways to calculate the energy lost in fittings and valves: the resistance coefficient method, and the equivalent length method. The method chosen will depend on what information is provided with the fitting to be analyzed.

Resistance Coefficient Method: Resistance coefficients are commonly reported by the manufacturers of liquid fittings and valves. The following equations and Table 26 (or manufacturer’s data) can be used to calculate friction loss in terms of resistance coefficient. There are methods that use up to 3 different resistance coefficients to improve the accuracy of the calculation.

Preview: Fluid Energy Loss in Fittings and Valves Calculator

hl = KF ( v2 / ( 2 g ) )

KF = ƒ ( Le / D )

where:

v = average velocity,
hl = head loss in units of length,
KF = resistance coefficient for the fitting or valve,
ƒ = friction factor given in the Moody diagram, Figure 4,
g = gravity (32.174 ft/sec2),
Le / D = equivalent length ratio given in table 1

Equivalent Length Ratio (Le/D) for Liquid Fittings and Valves
Table 1

Valve or Fitting Type
Le / D
Elbow
30
Swing Check Valve
100
Street Elbow
50
Ball Check Valve
150
Long Radius Elbow
20
Foot Valve (hinged)
75
45° Elbow
16
Close Return Bend
50
Tee (Flow Thru Run)
20
Tee (Flow Thru Branch)
60
Butterfly Valve (< 8")
45
Globe Valve
340
Ball Valve
3
Gate Valve
8
Gate Valve, 1/2 Closed
160

Equivalent Length Method: Pressure loss can be calculated for systems based on the equivalent length of straight pipe representing all pipe, fittings, and valves in the circuit. Equivalent lengths of some common fittings and valves for liquids can be found in Table 2 and 3.

Table 2
Nominal
Pipe
Size
(in.)
Elbows
90°
Std.
45°
Std.
90°
Long
Radius
90°
Street
45°
Street
Square
Corner
1⁄4
0.9
0.5
0.6
1.5
0.8
1.7
1⁄2
1.6
0.8
1.0
2.6
1.3
3.0
3⁄4
2.1
1.1
1.4
3.4
1.8
3.9
1
2.6
1.4
1.7
4.4
2.3
5.0
1-1⁄4
3.5
1.8
2.3
5.8
3.0
6.5
1-1⁄2
4.0
2.1
2.7
6.7
3.5
7.6
2
5.5
2.8
4.3
8.6
4.5
9.8
2-1⁄2
6.2
3.3
5.1
10.3
5.4
11.7
3
7.7
4.1
6.3
12.8
6.6
14.6
4
10.1
5.4
8.3
16.8
8.7
19.1
6
15.2
8.1
12.5
25.3
13.1
28.8
8
20.0
10.6
16.5
33.3
17.3
37.9
10
25.1
13.4
20.7
41.8
21.7
47.6
12
29.8
15.9
24.7
49.7
25.9
56.7

Table 3

Nominal
Pipe
Size
(in.)
Standard Tee
Flow
thru
Run
Flow
thru
Branch
1⁄4 0.6 1.8
1⁄2 1.0 4.0
3⁄4 1.4 5.1
1 1.7 6.0
1-1⁄4 2.3 6.9
1-1⁄2 2.7 8.1
2 4.3 12.0
2-1⁄2 5.1 14.3
3 6.3 16.3
4 8.3 22.1
6 12.5 32.2
8 16.5 39.9
10 20.7 50.1
12 24.7 59.7

 

Figure 4 Moody Diagram
Click on Image to Enlarge

Moody Diagram


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