Head loss due to Transitions and Fittings (Local loss)

Whenever flow velocity changes direction or magnitude in a conduit (e.g., at fittings, bends, and other appurtenances) added turbulence is induced. The energy associated with that turbulence is eventually dissipated into heat that produces a minor head loss, or local (or form) loss. The local (minor) loss associated with a particular fitting can be evaluated by

where V = mean velocity in the conduit (m/s, ft/s)

K = loss coefficient for the particular fitting involved.

The table given below provides the loss coefficients (K) for various transitions and fittings.

Table 3-3: Typical Minor Loss Coefficients

Type of form loss			K
Expansion	Sudden	D1 < D2
	Gradual	D1/D2 = 0.8	0.03
		D1/D2 = 0.5	0.08
		D1/D2 = 0.2	0.13
Contraction	Sudden	D1 > D2
	Gradual	D2/D1 = 0.8	0.05
		D2/D1 = 0.5	0.065
		D2/D1 = 0.2	0.08
Pipe entrance	Square-edge		0.5
	Rounded		0.25
	Projecting		0.8
Pipe exit	Submerged pipe to still water		1.0
Tee	Flow through run		0.6
	Flow through side outlet		1.8
Orifice	(Pipe diameter /orifice diameter)	D/d = 4	4.8
		D/d = 2	1.0
		D/d = 1.33	0.24
Venturi (long-tube)	(Pipe diameter /throat diameter)	D/d = 3	1.1
		D/d = 2	0.5
		D/d = 1.33	0.2
Bend	90o miter bend with vanes		0.2
	90o miter bend without vanes		1.1
	45o miter bend		0.2
Type of form loss (continued)			K
Bend	45o smooth bend: (bend radius /pipe diameter)	r/D = 1	0.37
		r/D = 2	0.22
		r/D = 4	0.2
	90o smooth bend	r/D = 1	0.5
		r/D = 2	0.3
		r/D = 4	0.25
	Closed return bend		2.2
Sluice	Submerged port in wall		0.8
	As conduit contraction		0.5
	Without top submergence		0.2
Valve	Globe valve, fully open		10
	Angel valve, fully open		5.0
	Swing check valve, fully open		2.5
	Gate valve, fully open		0.2
	Gate valve, half open		5.6
	Butterfly valve, fully open		1.2
	Ball valve, fully open		0.1

Source: Nicklow and Boulos (2005)