Energy and Hydraulic Grade Lines

EGL = z + \frac{p}{γ} + \frac{V ^{2}}{2 g} HGL = z + \frac{p}{γ}

EGL is the total head along the pipe; HGL is the piezometric head. EGL sits V²/2g above HGL. EGL drops where there is friction or a turbine; it jumps up across a pump. HGL may fall below the pipe (cavitation / siphon).

$EGL$ (m): Energy grade line
$HGL$ (m): Hydraulic grade line

Step-by-step solved example

p/γ+z = 30 m, V=4 m/s. EGL? g=9.81.

HGL is the piezometric line; EGL sits V²/2g above it.

1. Velocity head
V²/2g=16/19.62=0.815 m.
2. EGL
EGL=30+0.815=30.8 m.
$EGL = 30.8 m$

Answer: 30.8 m

10 practice questions

0/10 correct

1.HGL equals

2.EGL − HGL equals

3.A pump makes EGL

4.Friction makes EGL

5.If HGL is below the pipe centerline, p is

6.At a free surface of a reservoir, EGL and HGL

7.Sudden expansion: EGL

8.For the same Q, a larger D makes V²/2g

9.A turbine makes EGL

10.Bernoulli without loss: EGL is