Which statement best describes the hydraulic grade line?

Which statement best describes the hydraulic grade line?

• A. It estimates the energy grade line only
• B. It shows the sum of pressure head and elevation head
• C. It represents the lowest point of the system
• D. It measures water temperature

Answer: (B)

The hydraulic grade line represents the static head along a flow path, which is the sum of pressure head and elevation head. Pressure head comes from the fluid pressure at a point, expressed as how high a column of water that pressure could push up. Elevation head is the potential energy due to the water’s height above a reference level. Adding these two gives the total static energy per unit weight available to push water through the system, without including the energy associated with the water’s motion (velocity head). This is why the hydraulic grade line shows the sum of pressure head and elevation head. It’s different from the energy grade line, which also includes velocity head (the kinetic energy from moving water). It doesn’t measure temperature and isn’t about the lowest point of the system; it simply traces the static head along the network.

The hydraulic grade line represents the static head along a flow path, which is the sum of pressure head and elevation head. Pressure head comes from the fluid pressure at a point, expressed as how high a column of water that pressure could push up. Elevation head is the potential energy due to the water’s height above a reference level. Adding these two gives the total static energy per unit weight available to push water through the system, without including the energy associated with the water’s motion (velocity head).

This is why the hydraulic grade line shows the sum of pressure head and elevation head. It’s different from the energy grade line, which also includes velocity head (the kinetic energy from moving water). It doesn’t measure temperature and isn’t about the lowest point of the system; it simply traces the static head along the network.