Things You'll Need:
- Calculator
- Measuring tape
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Step 1
Measure the inside diameter of the hose and divide the measurement by 2. This is the radius of the hose. Where the diameter of the hose is 4 in., the radius is 4/2, or 2 in.
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Step 2
Subtract the water pressure at one end of the hose from the water pressure at the other end of the hose. If the water pressure at one end of the hose is 14.7 psi (atmospheric pressure only--a free flow, rather than a flow from a pressurized source) and at the other end of the hose it is also 14.7 psi, the math may say "0," but the answer is 1, since the difference of pressure must always be 1 or greater. If water pressure, like the pressure from a faucet, isn't involved, then the answer is 1. This is the "difference of pressure."
In this case, 14.7 - 14.7 = 1. -
Step 3
Multiply the length of the hose by the viscosity of the liquid. Viscosity is a measure of a liquid's resistance to flow, relative to water. Since you are calculating for water, which has a viscosity of 1, the result is simply the length of the hose. Multiply the result of that calculation by 8 (the coefficient of flow). This is the "length of hose."
If the liquid is water, with a viscosity of 1 and the hose is 72 in. long, then the length of hose is 8 x 72 = 576 -
Step 4
Multiply the radius of the hose by itself 4 times. This represents the area of the bore rather than the simple area of a circle; then multiply the result by 3.14159 (pi). This is the "area of hose."
Example: If the radius is 2 inches, then the radius to the fourth power is 16. The "area of hose" then is 16 x 3.14159 = 50.265. -
Step 5
Divide the "difference of pressure" by the "length of hose." Multiply the result by the "area of hose." The result is the flow of water through a hose or pipe in gallons per second.
The difference of pressure, 1, divided by the length of hose, 50.265 = 0.019, or about 0.2 gallons per second.
