calculating friction loss in hose lines is probably one of the most challenging parts of identifying required pump discharge pressures you must understand there are no shortcuts when it comes to identifying friction loss there is no set friction loss for any one size of hose friction loss is determined by the volume of water flowing through the line as well as the size and the length of the hose all three factors must be accounted for theoretical friction loss calculations are typically performed using the standard coefficient friction loss formula this formula requires three distinct values the friction loss coefficient of the hose which is provided by the hose manufacturer the volume of water moving through the hose and the length of the hose supplying the stream before we begin looking at calculations there are two distinct friction loss values we can identify total friction loss for the hose lay and friction loss of individual sections to obtain the theoretical friction loss based on the coefficient formula begin with the friction loss coefficient keep in mind that this number does vary between manufacturers and models of hose multiply by q squared q is our gpm divided by 100 finally multiply that by l which is the length of hose divided by 100 so let's begin by calculating the theoretical friction loss for the standard pre-connect attack line carried on our spartan engines feet inch and three-quarter national 8d hose flowing at 150 gpm we begin with the coefficient of our hose as provided by the manufacturer 12.49 q squared is our target flow rate for this example 150 gpm divided by 100 then squared 2.25 finally l is our length 250 feet divided by 100 2.5 after multiplying these numbers we obtain a friction loss of 70 psi or 14 psi per section of hose remember that the first concept of friction loss states that the longer the hose the greater the friction loss conversely the shorter the hose the lower the friction loss if we remove two sections or a hundred feet of our hose we will see that our total friction loss drops to 42 psi you will also notice that the friction loss per section remains the same at 14 psi the second friction loss concept states that if the hose diameter stays constant increasing volume increases friction loss if we increase our volume to 170 gpm our total friction loss will increase to 95 psi or 19 psi per second conversely if we lower our volume to only 130 gpm the friction loss drops to a meager 52 psi or only 10 psi per section as you can see as the volume is increased or decreased the friction loss per hose section will also increase or decrease the final friction loss concept we will discuss in this video is the third concept which states that as the diameter of the hose line increases friction loss decreases exponentially if we start by looking at flowing the same amount of water 150 gpm through 250 feet of two and a half inch hose our coefficient drops to two and our total friction loss drops to 15 psi or only 3 psi per section so let's look at what happens when we supply a blitz fire with 500 gpm through two and a half inch compared to three inch hose using our formula we can see the theoretical friction loss for our two and a half inch hose comes out to 25 psi per section however by increasing our hose diameter by only half an inch we can drop the friction loss to only 10 psi per section on our three inch hose as you can see it is critical to ensure proper hose line selection when supplying master streams to ensure efficient utilization of the pump and reduce engine rpms there is one caveat to remember when calculating theoretical friction loss based on hose coefficients these values are obtained by the manufacturer in a controlled environment using brand new hose depending on the age and condition of your current hose it is very likely that the true friction loss for your hose will vary significantly from theoretical models the only way to truly identify required pump pressures adequate volume and accurate friction loss values is to perform routine flow testing of your apparatus this allows operators the opportunity to obtain practical friction loss values and flow rates at a variety of pump pressures in hose lengths