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

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Hydraulic and Pneumatic Knowledge

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

h_l = K_F ( v² / ( 2 g ) )

K_F = ƒ ( L_e / D )

where:

v = average velocity,
h_l = head loss in units of length,
K_F = resistance coefficient for the fitting or valve,
ƒ = friction factor given in the Moody diagram, Figure 4,
g = gravity (32.174 ft/sec²),
L_e / 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