Loss Coefficient

Loss coefficient, abbrevated as K, a dimensionless number, measures the minor loss to the change in velocity due to friction thru pipes, fittings, and valves.  Most piping consists of more than just straight lines, these losses are termed a minor loss.  Any bend or tee, expansion or contraction, valve opening or partially closing can cause minor or even major losses.

 

Loss coefficient formula

\(\large{ K = h_l \; \frac { 2 \; g  } { v^2 }  }\)

Where:

Units	English	Metric
\(\large{ K }\) = loss coefficient	\(\large{ dimensionless }\)
\(\large{ g }\) = gravitational acceleration	\(\large{\frac{ft}{sec^2}}\)	\(\large{\frac{m}{s^2}}\)
\(\large{ h_l }\) = head loss	\(\large{ ft }\)	\(\large{ m }\)
\(\large{ v }\) = velocity of flow	\(\large{\frac{ft}{sec}}\)	\(\large{\frac{m}{s}}\)

 

Loss Coefficient Table

Component	Loss Coefficient \(K\)
Elbows
90 Short Elbow, flanged	0.3
90 Short Elbow, threaded	1.5
90 Long Elbow, flanged	0.2
90 Long Elbow, threaded	0.7
45 Long Elbow, flanged	0.2
45 Short Elbow, threaded	0.4
180 Return
180 Return, flanged	0.2
180 Return, threaded	1.5
Tees
Line flow, flanged	0.2
Line flow, threaded	0.9
Branch flow, flanged	1.0
Branch flow, threaded	2.0
Union, threaded	0.08
Valves
Diaphragm, fully open	2.3
Diaphragm, 1/4 closed	21
Diaphragm, 1/2 closed	4.3
Globe, fully open	10
Angle, fully open	2
Gate, fully open	0.15
Gate, 1/4 closed	0.26
Gate, 1/2 closed	2.1
Gate, 3/4 closed	17
Swing Check, forward flow	2
Swing Check, backward flow	\(\infty\)
Ball, fully open	0.05
Ball, 1/3 closed	5.5
Ball, 2/3 closed	210
Water meter	7