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 |
Tags: Coefficient Equations Friction Equations Hydraulic Equations Head Equations