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Published bySydni Foden Modified about 1 year ago

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Smooth Bore Nozzles vs. Combination Nozzles How is a fire stream best formed?

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Smooth Bore Nozzles Advantages: Simple in design Inexpensive Disadvantages: Has only one correct operating pressure to develop optimum velocity and reach Tip size must be changed to change flow Must have variety of tips for different flows No fog capabilities Not effective for mechanical ventilation Advantages: Simple in design Inexpensive Disadvantages: Has only one correct operating pressure to develop optimum velocity and reach Tip size must be changed to change flow Must have variety of tips for different flows No fog capabilities Not effective for mechanical ventilation

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Unequal Velocity of Smooth Bore Greater velocity at center of stream Lower velocity at outside of stream Caused by side wall turbulence Causes outside of stream to “peel” away Less reach than straight stream from combination nozzle Side Wall Friction Center "core" at higher velocity than outer circle of stream. Stream expansion begins upon exiting tip

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Equal Velocity of Combination Nozzle Equal velocity across stream Partial vacuum within the pattern focuses stream a short distance from the nozzle Re-converged stream has a uniform cross-sectional velocity Tighter stream with more reach than smooth bore Partial Vacuum Water exits nozzle at EQUAL velocity and pressure Focused Point

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Equal Velocity of Combination Nozzle Partial Vacuum Water exits nozzle at EQUAL velocity and pressure Focused Point

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At Equal Flows... Which stream has more reach?

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At Equal Flows... Combination Nozzle Reaches Farther Than Smooth Bore Nozzle

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Straight Stream From Combination Nozzle... Because of higher nozzle pressure & velocity than smooth bore, combination nozzle stream hits harder Not hollow as seen by Pitot gauge pressure reading at focal point

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Impact Force of Stream F = M V Force = Mass times Velocity Force = Mass times Velocityor WV WV g M = Mass of water /unit of time V = Velocity of water /unit of time W = Weight of water /unit of time W = Weight of water /unit of time g = Gravitational constant 32.2 ft/sec 2 F = M V Force = Mass times Velocity Force = Mass times Velocityor WV WV g M = Mass of water /unit of time V = Velocity of water /unit of time W = Weight of water /unit of time W = Weight of water /unit of time g = Gravitational constant 32.2 ft/sec 2 F =

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Impact Force of 150 GPM Stream... WV WV 32.2 ft./sec ft./sec. 2 W = 150 GPM x 8.34 lb./gal = 1251 lb./min. W = 1251 lb./min. divided by 60 sec./min. W = lb./sec. V = 150 GPM 7/8” Smooth 44 psi = 80 ft./sec. (54.5 MPH) Combination 75 psi = ft./sec. (72.9 MPH) Combination 100 psi = 121 ft./sec. (82.5 MPH) WV WV 32.2 ft./sec ft./sec. 2 W = 150 GPM x 8.34 lb./gal = 1251 lb./min. W = 1251 lb./min. divided by 60 sec./min. W = lb./sec. V = 150 GPM 7/8” Smooth 44 psi = 80 ft./sec. (54.5 MPH) Combination 75 psi = ft./sec. (72.9 MPH) Combination 100 psi = 121 ft./sec. (82.5 MPH) F =

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Comparison of 150 GPM Nozzle TypeNozzle PressureVelocity 7/8” Smooth Bore 44 psi54.5 mph Combination Nozzle 75 psi72.9 mph Combination Nozzle100 psi82.5 mph Nozzle TypeNozzle PressureVelocity 7/8” Smooth Bore 44 psi54.5 mph Combination Nozzle 75 psi72.9 mph Combination Nozzle100 psi82.5 mph

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7/8” Smooth 44 psi lb./sec. x 80 ft./sec lb./sec. x 80 ft./sec ft./sec ft./sec. 2 Combination 75 psi lb./sec. x ft./sec lb./sec. x ft./sec ft./sec ft./sec. 2 Combination 100 psi lb./sec. x 121 ft./sec lb./sec. x 121 ft./sec ft./sec ft./sec. 2 7/8” Smooth 44 psi lb./sec. x 80 ft./sec lb./sec. x 80 ft./sec ft./sec ft./sec. 2 Combination 75 psi lb./sec. x ft./sec lb./sec. x ft./sec ft./sec ft./sec. 2 Combination 100 psi lb./sec. x 121 ft./sec lb./sec. x 121 ft./sec ft./sec ft./sec. 2 F = = 51.8 lb. Force F = = 69.2 lb. Force F = = 78.3 lb. Force Comparison of Impact 150 GPM

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Comparison of Nozzle Reaction 150 GPM Nozzle Nozzle Pressure Reaction Force 7/8” Smooth 44 psi52.8 lb. force Combination 75 psi67.5 lb. force Combination 100 psi79.2 lb. force Nozzle Nozzle Pressure Reaction Force 7/8” Smooth 44 psi52.8 lb. force Combination 75 psi67.5 lb. force Combination 100 psi79.2 lb. force

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Impact Force & Velocity... Combination nozzle has higher velocity Smooth Bore has lower velocity Higher velocity with same flow equals more force Therefore, harder hitting stream is typically realized from combination nozzle at higher pressure Combination nozzle has higher velocity Smooth Bore has lower velocity Higher velocity with same flow equals more force Therefore, harder hitting stream is typically realized from combination nozzle at higher pressure

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Stream Impact Testing... Flow of 160 GPM (typical of smooth bore & combination nozzles) Differing distances and target sizes used Flows & Pressures closely monitored for valid test results Results: Harder hitting, farther reaching stream from combination nozzles because of higher stream velocity

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