Since we're going back to basics, let's talk friction loss. Friction loss is one of those “nerdy” topics, but it is one of the specs we are asked for most often (which is why we built a calculator!). So, let’s dive in and break it down.
What Is Friction Loss?
Simply put, friction loss is the reduction in water pressure that occurs as water moves through a hose. It’s caused by the friction between the water and the internal surface of the hose. The more friction there is, the less efficient your hose becomes, leading to lower flow rates and, ultimately, less water reaching the nozzle.
In his article on FireRescue1, Battalion Chief Robert Avsec (ret.) laid out five principles that every pump operator should commit to memory:
- All fire hose has friction loss.
- There is no set friction loss for any one size of hose.
- Friction loss is determined by the gpm flowing, the size of the hose and the length of the hose. All three factors must be considered.
- Most of the fog nozzles have flow rates ranging from 95 to 200 gpm. Don’t get stuck on one flow rate; the fire will dictate which flow rate to use.
- It’s not psi that puts the fire out; it’s providing the correct gpm that the incident commander needs.
Why Does Friction Loss Matter?
On the job, proper flow is critical in getting adequate water on the fire. Whether you're working with a 100 psi fog nozzle or a 50 psi smoothbore, the pressure rating affects the water output. Lower PSI at the nozzle means lower GPMs.
With low psi nozzles specifically not only would that mean less water on the fire, but it would also risk hose kinking as there would be less internal pressure in the line to keep it expanded. A poorly performing hose with high friction loss can mean the difference between quickly suppressing a fire and letting it spread.
Additionally, higher friction loss puts more pressure on the pumper, especially in challenging scenarios like high-rise operations, where water has to travel longer distances vertically. In those cases, the pumper has to work harder to maintain adequate pressure, which can strain the equipment and potentially reduce water output at the nozzle.
"The basic challenge for the pump operator is to develop the proper pump discharge pressure necessary to overcome the friction loss in a fireground set up to ensure that the firefighter on the nozzle will have the appropriate amount of water to suppress the fire." – BC Robert Avsec (ret.)
As a manufacturer, our objective is to design hoses that minimize friction loss while maintaining durability and flexibility – which is exactly what our Mertex lining does.
WHAT FACTORS AFFECT FRICTION LOSS?
Friction loss isn’t a one-size-fits-all problem—it’s influenced by several factors, and as a firefighter, you’ll want to keep these in mind:
- Hose Diameter: Larger hoses allow water to flow more freely, meaning less friction loss. For example, a 1.75” hose will have more friction loss than a 2.5” hose at the same flow rate, simply due to the difference in space inside the hose.
- Flow Rate: The faster water flows through the hose, the more friction it creates. It’s basic physics—the more speed, the more contact with the walls of the hose.
- Hose Length: The longer the hose, the more opportunities there are for friction to reduce water pressure. For every 100 feet of hose, you’re adding more resistance.
- Hose Condition: A well-maintained hose will always perform better. Cracks, internal wear, or even dirt build-up can increase friction over time, which is why routine inspection and care are essential.
Beyond the hose itself, elevation impacts friction loss significantly. Additional friction loss is calculated at 0.433 psi per foot of elevation.
How Do We Combat Friction Loss?
At Mercedes Textiles, we put a lot of thought into reducing friction loss from the start. It all begins with the materials and processes. Our hoses are built with high-quality linings that minimize resistance, meaning smoother water flow.
We also focus on the external durability of the hose. A hose that’s kinked, twisted, or damaged will have higher friction loss, which is why our hoses are designed to be flexible, kink-resistant, and tough enough to withstand the harsh conditions you face in the field.
And don’t forget—proper coupling is critical. A secure, high-quality coupling ensures that water flows smoothly from the pump through the hose, reducing any unnecessary pressure drops. All these details, when added together, make a significant difference.
How You Can Manage Friction Loss
Even the best hose can’t eliminate friction loss completely, but there are strategies you can use on the job to keep it under control:
- Use the right size hose for the job: Determine the right diameter for the necessary flow based on the job at hand. Overpumping a smaller line to get higher flows will actually create more friction loss as well. Opting for the larger diameter hose will reduce friction loss.
- Limit hose length where possible: The longer the hose, the more friction you’ll encounter. When practical, try to minimize the distance between the water source and the nozzle.
- Dial in your flows: Use flow meters and gauges to test and measure flow rates for each of your lines. Create charts or other quick references for the pump operator.
- Maintain your equipment: Keep your hoses in top condition. Routine inspections and maintenance ensure that the inner lining remains smooth and free from debris.
FireRescue1 has a great resource on how to calculate friction loss and overcome its effects on the fireground.
Final Thoughts
At the end of the day, friction loss might seem like one of those minor details in the grand scheme of firefighting, but as you know, every detail matters when you’re battling flames. Understanding it, and how to manage it, means you’re staying one step ahead—prepared and ready for whatever comes your way.
Stay safe, stay knowledgeable, and don’t forget to keep learning! Curious about other aspects of your hose? Check out other #KnowYourHose resources for more tips, guides, and nerdy insights into firefighting tools and techniques.