Friction Loss: Everything You Need to Know

Friction loss is the pressure loss in the pipe or tubing caused by friction between water and the inner walls of the pipe. The higher the water flows through the tubing and the faster it moves, the greater the pressure loss.

In this post, we discuss everything you need to know about friction loss, including the factors affecting it, how it is calculated, and how to prevent it in pipe systems.

What is Friction Loss

Friction loss refers to the loss of energy or pressure of water flowing in your piping system due to friction between moving water and the pipe surface. As water flows through the tubing, it carries energy with it. Whenever there is resistance to the flow rate, it diverts water and allows energy to escape. These competing forces cause friction loss in tubing or pipes. Friction loss affects the overall pressure of the irrigation system, and if it gets too high, it can prevent emitters from operating effectively.

Fast water flow, larger pipe lengths, and smaller diameter tubing might be expected to experience significant pressure losses due to friction. Too much friction loss can drop the pressure to the point where the irrigation system does not function properly.

Factors that Affect Friction Loss in Tubing

The factors affecting friction loss in an irrigation piping system include flow rate, length of tubing, the tubing material, and its diameter. Here's a detailed look at the factors and causes of friction loss.

Flow Rate

In terms of pressure drop, flow may be broken down into two variables: volume and velocity. Velocity is measured in feet per second, whereas flow is measured in GPM or GPH. Higher flow rates and larger volumes cause more friction loss as the water velocity and energy dissipate against the pipe walls.

Pipe Material

The material of the tubing also influences friction loss. Friction increases with the roughness of the material. Plastic tubing, such as polyethylene, PVC, and PEX, has less friction than metal tubing. Rougher pipe surfaces, such as those with scale or rust buildup, generate greater friction than smooth surfaces.

Tubing Length

The greater the distance the water travels, the more friction it will experience. Irrigation fittings (tees, elbows) and turns can also contribute to friction loss. Longer pipe runs naturally have a higher friction loss than shorter runs due to greater contact between water and tubing walls.

Tubing Diameter

Friction loss is typically higher in smaller-diameter pipes due to increased water velocity and contact area. Larger tubing interior diameters have less friction. This is because a smaller percentage of the water contacts the tubing's walls. Friction is caused by contact with the walls, so bigger diameter tubing has lower rates of pressure loss by friction.

Importance of Calculating Friction Loss

The performance of the irrigation system is the primary reason for calculating friction loss. If too much pressure is lost due to friction, there won't be enough pressure to run the emitters. Even if there is enough pressure to operate the emitters, it may not be enough to maintain consistency with the rest of the system. This can cause issues such as plants farther down the line receiving insufficient water or plants closer to the source receiving too much water.

If you don't calculate friction loss, you may purchase a tubing diameter greater than you require, resulting in a higher cost. On the other hand, if you buy tubing with a diameter that is too small, it will most likely need to be changed.

The costs of changing tubing are substantially higher because of the time involved in installing it and potential crop losses due to poor irrigation system performance. Therefore, planning is important to save money and ensure your system runs well.

Protect Your Irrigation System

Another reason to consider friction loss and prevent it is the protection of your system. High water velocity can damage fittings, emitters, valves, and other system components. Additionally, if the water velocity is excessively high, you may experience a "water hammer." High velocities can also displace the pipe due to movement, which may damage the outside of the tubing. High water velocities can even reach erosion levels, causing significant damage quickly.

As a rule, the velocity should not exceed 5 feet per second. This is random, but 6 feet per second or less works fine by reducing the sound of the water going through the tube.

Calculating Friction Loss

When you Google "how to calculate friction loss," it brings a huge range of material, ranging from general guidelines to complex calculations. If you're designing a large irrigation system, doing the math yourself is recommended. However, if you're a home DIYer, you can use Washington State University's Calculator for friction loss. There is another calculator for calculating velocity and pipe diameter.

Ways to Reduce Friction Loss

Here are a few ways to minimize friction loss and promote steady flow.

Use Larger Tubing Diameters

Larger pipes allow for slower water velocities, which reduces friction. By increasing tubing diameters, you ensure that water does not have to work as hard to get through pipes. As a result, you will reduce flow resistance and friction loss in pipes. Just make sure you're supporting larger pipes with sturdy, efficient pipe supports.

Reduce Interior Roughness

Pipes with smoother interior surfaces have lower friction. Smoothing off internal pipe surfaces creates a clear path for water to flow. This includes cleaning pipes and keeping them clear of debris.

It also involves protecting pipes from corrosion. Pipe corrosion leads to costly dips and obstructions, so it's critical to prevent corrosion from penetrating pipe surfaces and eating away.

Minimize Fittings and Turns

Fittings such as elbows, tees, and valves cause flow disruptions, which increase friction. To avoid friction loss, straighten your pipes and clear their path. Remove fittings, tees, and other sharp turns whenever possible.

Conclusion

Understanding and reducing friction loss is essential to save costs and boost system performance. Whether your irrigation system is for a home or commercial property, you must maintain adequate pressure when it is running. If you're a home DIYer, follow these guidelines to prevent friction loss and improve system efficiency. Larger commercial growers need to calculate and plan for friction loss and get professional help. Online calculators can perform calculations for the end user with minimal input, which should be simple to obtain. Now that you understand the importance of proper pipe sizing and friction loss, you can design an appropriate irrigation system for your garden.