Hoses provide the ultimate in utility and flexibility in moving a liquid or gas from one place to another safely and efficiently. A wide assortment of hoses are available for domestic and gardening use, industrial applications and in fighting fires. In every case, hose-system designers seek to provide maximum flow with minimum pressure losses, and they use Bernoulli’s Principle, which simply states that flow through a tube is proportional to the square root of pressure change through a system. You can calculate flow from pressure information using published hose data.
Define the flow application. In this example, a 50-foot garden hose with a 5/8-inch ID (0.625-inch inner diameter) is being used to fill a pressurized tank with 5 psi of fixed pressure. The water pressure at the hose connection to a well pump is 45 psi. From this information you can calculate water flow through the hose using pressure.
Calculate the total pressure drop or differential through the 50 feet of hose. Subtract the outlet pressure, 5 psi, from the inlet pressure, 45 psi, to yield the 40 psi total loss through the hose.
Look up the flow rate for 40 psi of head loss through 50 feet of 5/8-inch ID hose. In this case, data for Schedule 40-PVC plastic pipe of the same inner diameter may be used to determine the flow. Schedule 40-PVC plastic pipe has an inner diameter of 0.622 inches. The pressure-loss data for this pipe shows 35.5 psi loss for 10 gallons per minute (gpm) through 100 feet of pipe. To compute the flow for 40 psi through 50 feet of hose, take the square root of (40 psi loss/[35.5/100 feet/50 feet]) and multiply by 10 gpm to yield 15.01 gpm.
Define the fire hose application. A 100-foot, 3-inch-diameter fire hose is being tested for use to drain a large swimming pool using a pump that delivers 55 psi. You can calculate the flow through the fire hose with this information.
Look up the specific flow vs. pressure data for the fire hose. The manufacturer’s pressure loss data shows that a 3-inch ID hose loses 57.8 psi for an 850 gpm flow.
Calculate the exact flow rate by correcting the data to actual pressure loss. Take the square root of 55 psi/57.8 psi, which is 0.9755, and multiply by 850 to get 829.16 gpm.