How to Calculate Head Loss in a Pumping Installation

How to Calculate Head Loss in a Pumping Installation

March 20, 2022

One of the most misunderstood physical characteristics of a pump is the concept of the head. What exactly is a pump's head? In layman terms, a pump's head can be defined as the maximum height that a pump can achieve if it's pumping against gravity.

The head can vary accordingly with horizontal distances and vertical heights.

In horizontal distances, head losses are potential energy that has been lost because of frictional resistance of the piping system (pipe, valves, fittings, and entrance and exit losses).

In vertical heights, it is the back pressure falling over the pump in vertical head.

It commonly occurs when the liquid loses momentum as it flows and is dependent on factors including fluid viscosity, diameter, length of the pipes, and pipefittings and accessories involved.

Unlike velocity head, friction head cannot be ignored in system calculations. Head loss values vary as the square of the flow rate. Head losses can be a significant portion of the total head.

In this write-up, we'll be looking at how you can accurately measure head loss within pumping installations.

Calculation of Head Loss

As a fluid moves through a pipeline, friction occurs due to the interaction between the moving fluid and the stationary pipe wall. The friction generated here converts some of the fluid's hydraulic energy to thermal energy. Head loss within pipeline systems happens as a result of this conversion.

Head loss in pipelines due to Newtonian fluids ( A Newtonian fluid is defined as one with constant viscosity, with zero shear rate at zero shear stress, that is, the shear rate is directly proportional to the shear stress.) is commonly calculated using the Darcy Weisbach Equation:

HL = Head Loss in meter/feet
f = Friction Factor
L = Length of the Pipe being considered in meter/feet
D = Internal Diameter of the Pipe in meter/feet
V = Mean velocity of the fluid m/s or ft./s
g = acceleration due to gravity in 9.81 m/s2 or 32.15 ft./s2

The friction factor (f) here is dependent on flow velocity, pipe diameter, the pipe, fluid density and viscosity, as well as pipe roughness.

Key Takeaways:
  • HL is directly proportional to pipe length.
  • HL is inversely proportional to the pipe diameter.

Friction factor for smooth pipes can be calculated using the Blasius equation:

F = 0.079/Re1/4

To calculate HL for Reynolds numbers greater than 100,000 and for rough pipes, one needs to make use of the Moody Diag.

Factors that Influence Head Loss

Pipe Material

Pipe sizes and schedules are often limited by specific construction materials used. Additionally, pipe roughness also increases HL.

Pipe Material Absolute Roughness (inches) Reynolds Number Darcy Factor Head Loss (feet)
PVC 0.00006 285,520 0.015 6.9
Steel 0.0018 285,520 0.018 8.5
Galvanized 0.006 285,520 0.022 10.6
Cast Iron 0.0102 285,520 0.025 12.1

Pipe Size

Irrespective of the material used, pipes are available in varying sizes, schedules, and wall thickness. To calculate HL, users must use nominal pipe size and not the actual ID.

Fluid Property

The properties of a given fluid also play a significant role in determining the head loss within a pipeline. For one, head loss will be greater in highly viscous fluids. Additionally, pipe head loss may also be affected by changes to the fluid temperature.

There’s far more to be said about head loss and pumping systems. We’ve only scratched the surface in this blog. If you’d like to learn more, get in touch with one of our application engineers who would love to discuss this at length. If you are planning to design a pumping system, we can help you with a range of products and services including, pumps, motors, pipes, fittings, installation and more.

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