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Smooth Bore Nozzles vs. Combination Nozzles

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

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Smooth Bore Nozzles vs. Combination Nozzles

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

  2. Smooth Bore Nozzles Advantages: • Simple in design • Inexpensive Disadvantages: • Has only onecorrect 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

  3. Stream expansion begins upon exiting tip Center "core" at higher velocity than outer circle of stream. Side Wall Friction 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

  4. Focused Point Partial Vacuum Water exits nozzle at EQUAL velocity and pressure 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

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

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

  7. At Equal Flows...Combination Nozzle Reaches FartherThan Smooth Bore Nozzle

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

  9. F = M V Force= Mass times Velocity or WV g M = Mass of water /unit of time V = Velocity of water /unit of time W = Weight of water /unit of time g = Gravitational constant 32.2 ft/sec2 F = Impact Force of Stream

  10. F = WV 32.2 ft./sec.2 W = 150 GPM x 8.34 lb./gal = 1251 lb./min. W = 1251 lb./min. divided by 60 sec./min. W = 20.85 lb./sec. V=Velocity @ 150 GPM 7/8” Smooth Bore @ 44 psi = 80 ft./sec. (54.5 MPH) Combination Nozzle @ 75 psi = 106.9 ft./sec. (72.9 MPH) Combination Nozzle @ 100 psi = 121 ft./sec. (82.5 MPH) Impact Force of 150 GPM Stream...

  11. Comparison of Velocity... @ 150 GPM Nozzle Type Nozzle Pressure Velocity • 7/8” Smooth Bore 44 psi 54.5 mph • Combination Nozzle 75 psi 72.9 mph • Combination Nozzle 100 psi 82.5 mph

  12. Comparison of Impact Force... @ 150 GPM 7/8” Smooth Bore @ 44 psi 20.85 lb./sec. x 80 ft./sec. 32.2 ft./sec.2 Combination Nozzle @ 75 psi 20.85 lb./sec. x 106.9 ft./sec. 32.2 ft./sec.2 Combination Nozzle @ 100 psi 20.85 lb./sec. x 121 ft./sec. 32.2 ft./sec.2 F = = 51.8 lb. Force F = = 69.2 lb. Force F = = 78.3 lb. Force

  13. Comparison of Nozzle Reaction Force... @ 150 GPM Nozzle Type @ Nozzle Pressure Reaction Force • 7/8” Smooth Bore @ 44 psi 52.8 lb. force • Combination Nozzle @ 75 psi 67.5 lb. force • Combination Nozzle @ 100 psi 79.2 lb. force

  14. 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

  15. 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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