The energy grade line (EGL) represents the total energy head of flowing water in a pipe, accounting for velocity head, and illustrates how energy decreases due to friction and other losses. The hydraulic grade line (HGL) reflects the pressure available to the fluid and is always positioned one velocity head below the EGL. Both lines are crucial for understanding fluid flow dynamics and pressure variations in piping systems.

1. 1
Energy Grade Line
A line that represents the elevation
of energy head (in feet or meters) of water
flowing in a pipe or channel.
The line is drawn above the
hydraulic grade line (gradient) a distance
equal to the velocity head (V2
/2g) of the
water flowing at each section or point
along the pipe or channel.

2. 2

3. 3
Energy Grade Line
and can be expressed as:
EL = H = p / γ + v2
/ 2 g + h = constant
along a streamline
where
EL= Energy Line (m)
and can be expressed as:

4. 4
Energy Grade Line
• For a fluid flow without any losses due
to friction (major losses) or components
(minor losses) - the energy line would
be at a constant level. In a practical
world the energy line decreases along
the flow due to losses.

5. 5
Energy Grade Line
• A turbine in the flow reduces the
energy line and a pump or fan in the
line increases the energy line.

6. 6
Hydraulic Grade Line
The Hydraulic Grade Line is a line representing the
total head
available to the fluid - minus the velocity head and
can be expressed as:
HGL = p / γ + h
where
HGL = Hydraulic Grade Line (m)

7. 7
Hydraulic And Energy Grade Line
• The hydraulic grade line lies one velocity
head below the the energy line.

8. 8
EGL And HGL
In case the cross section is constant along the streamline and
the flow steady, discharge remains constant and also so does
velocity. Therefore, velocity head remains the same as well.
In that case, HGL will always remain parallel to EGL.

9. 9
Applications of EGL and HGL
• APPLICATION OF HYDRAULIC GRADE LINE:-
• 1)The hydraulic grade line indicate the pressure
along the pipe
• 2)The vertical distance from the pipe to the
hydraulic grade line is the pressure head at that
point
• 3)The slope of hydraulic grade line is the measure of
the rate of head loss

10. 10
• 4)Change in elevation of the hydraulic
grade line is due to change in velocity
and diameter
• 5)At pipe outlet pressure head is zero so
the pipe elevation and the hydraulic
grade line coincide

11. 11
Applications Cont:
• 6) The hydraulic grade line is a straight
line only if the pipe is straight and of
uniform diameter
• 7) Energy grade line shows the rate at
which the energy decreases in a pipe.