ENERGY LOSS IN PIPE AND TUBE BENDS Table 24. Bend Equivalent Length Ratio, L e /D Machinery's Handbook, 31st Edition
2783
Bend Angle R / D L e / D
Bend Angle R / D L e / D
Bend Type
Bend Type
30° 45° 60° 90°
… 8 … 15 … 25 … 60 … 50
1 20 2 12 3 12 4 14
Miter Bend
6 17 Close Return Bend
180°
Radius Bend
90°
8 24 10 30 12 34 16 42 R / D is the bend mean radius divided by pipe diameter
The loss of head due to a bend in the pipe is most frequently given as the equivalent length of straight pipe, which would cause the same loss in head as the bend. Experiments show that a right-angle bend should have a radius of about three times the diameter of the pipe. Assuming this curvature, then, if d is the diameter of the pipe in inches, and L is the length of straight pipe in feet that causes the same loss of head as the bend in the pipe, the following formula gives the equivalent length of straight pipe that should be added to simulate a right-angle bend: L 4 d 3 ÷ = Energy Loss in Fittings and Valves.— 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 25 (or manufacturer’s data) can be used to calculate friction loss in terms of resistance coef- ficient. There are methods that use up to 3 different resistance coefficients to improve the accuracy of the calculation. h l K F v 2 = K F where v is average velocity, h l is head loss in units of length, K F is the resistance coefficient for the fitting or valve, f is the friction factor given in the Moody diagram, Fig. 1, and L e / D is the equivalent length ratio given in Table 25. Table 25. Equivalent Length Ratio ( L e / D ) for Liquid Fittings and Valves Fitting or Valve Type L e / D Fitting or Valve Type L e / 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 Ball Valve 3 Close Return Bend 50 Gate Valve 8 Tee (Flow thru Run) 20 Gate Valve, 1/2 Closed 160 Tee (Flow thru Branch) 60 Butterfly Valve (< 8 ″ ) 45 Globe Valve 340 Valves fully open unless otherwise specified. 2 g --- f L e D = ---
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online