The term “pump head” refers to the energy that a pump adds to the fluid being pumped in order to overcome system resistance. Understanding how to calculate pump head is essential for anyone working with pumps, as the correct calculation ensures efficient performance and can prevent problems such as cavitation and under-performance. In this article, we will discuss the methods used to calculate pump head and provide practical examples that will help you improve your understanding of pumps and their operation.

Static head

Static head, also known as elevation head, refers to the vertical distance between the liquid level of the suction source (such as a tank or reservoir) and the discharge point. To calculate this value, simply measure the vertical distance between both points. Keep in mind that negative static head occurs when the discharge point is lower than the suction source level.

Friction head

Friction head represents the resistance caused by friction in the pipe system, valves, and fittings. To calculate friction head, you’ll need to determine three factors: pipe length, pipe material, and fluid velocity.

1. Measure the length of all pipes in your system (including both the suction and discharge sides).

2. Identify your pipe material’s friction factor using data available on reference charts or from manufacturer specifications.

3. Calculate fluid velocity using the following formula:

Velocity (ft/s) = Flow rate (gpm) / (0.408 x Internal Pipe Area (sq ft))

Once you have these values, you can compute friction head using Darcy-Weisbach equation:

Friction Head (ft) = Friction Factor x Pipe Length (ft) x Fluid Velocity^2 (ft/s) / (2 x Gravity constant x Internal Pipe Diameter)

Pressure head

Pressure head represents the pressure difference between inlet and outlet of the pump expressed in terms of height. To calculate pressure head, measure inlet and outlet water pressure’s difference in psi (pound per square inch) at the pump and convert it to feet using the formula:

Pressure Head (ft) = (Pressure difference in psi) x 2.31 / Fluid Specific Gravity

Putting it all together: Total Dynamic Head

Now that we have calculated static head, friction head, and pressure head, it is time to combine them to determine the total dynamic head. The total dynamic head (TDH) tells you how much energy the pump must provide to overcome resistance within the system. You can find the TDH following this equation:

Total Dynamic Head (ft) = Static Head + Friction Head + Pressure Head

Final thoughts

Calculating pump head may seem complex at first; however, understanding the concepts of static head, friction head, and pressure head, and breaking down the calculations step by step will make the process much more manageable. By correctly calculating pump head, you’ll be able to select an appropriate pump for your system’s needs and ensure efficient operation.