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# Friction Loss & Flow

 Flow Rate Calculator Pipe Length = ft Pipe Diameter = ft Cross Sectional Area = ft² Flow Rate = gpm Pipe Velocity = ft/sec Friction Factor = Friction Loss =

## Friction Loss/Flow Calculations

Several methods are available to determine the friction losses and estimated water flow rates in pipes. In this section one of the most widely used formulas for friction loss, the Darcy-Weisback equation, will be presented so the user can have an understanding of the use of these formulas and the information they can provide.

The Darcy-Weisback formula is:

 Friction Loss (hf ) = f L x V2 d 2g hf = Friction Loss (ft) f = Friction Loss Factor L = Pipe Length (ft) d = Pipe Diameter (ft) v = Pipe Velocity (ft/sec) g = 32.2 lb m - ft (Acceleration of Gravity Factor) lb f - sec2

A simple method to estimate flow rate is the "drum and stopwatch method." Place a drum or container of sufficient size (30 to 50 gallons) at the end of the pipe and, using a stopwatch, estimate the time to fill the container. This will provide a good method to determine the flowrate that can be used in these calculations if a flowmeter is not available.

## Sample Calculations:

Determine the friction loss of water pumped through 1,000 ft. of 4-inch diameter pipe at a 300 gpm flow rate. Flowrate can be determined using a flowmeter or the "drum and stop watch method."

The first step is to determine the velocity based on the pipe's cross-sectional area.

 Cross-sectional Areas = π x (pipe radius)² Where π = 3.14 Pipe Diameter = 4-inch = .33 ft Pipe Radius = 2-inch = .16 ft Cross-sectional Area = 3.14 x (.16)² = .08 ft²

The second step is to determine the pipe velocity.

 Pipe Velocity (V) = Flow rate Cross Sectional Area Multiply the 300 gpm flow rate by .002 to convert to ft3/sec 300 gpm x .002 = 0.60 ft3 /sec Calculate Pipe Velocity Velocity (ft/sec) = 0.60 0.08 Velocity (ft/sec) = 7.5 ft/sec
 Using a .02 friction factor, calculate the friction loss Friction Loss (h f ) = f L x V² d 2g Friction Loss (ft) = .02 x 1000 ft x (7.5 ft/sec)² .33 ft 64.4 Velocity (ft/sec) = 52.9 ft

## Legend

 L/S = Liters per Second gpm = Gallons per Minute HP = Horsepower KW = Kilowatt m/s = Meters per Second m³ = Cubic Meters m² = Square Meters ft² = Square Feet ft³ = Cubic Feet

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