Related Resources: calculators

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

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.

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