Skip to content

Orifices

Fluid Mechanics · FE Reference Handbook section

Fluid Mechanics
2 formulas
10 exam-style examples
~49 min
All Fluid Mechanics lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • The cross-sectional area at the vena contracta A2 is characterized by a coefficient of contraction Cc and given by Cc A0.
  • where C, the coefficient of the meter (orifice coefficient), is given by
  • Bober, W., and R.A. Kenyon, Fluid Mechanics, Wiley, 1980. Diagrams reprinted by permission of William Bober and Richard A. Kenyon.
  • For incompressible flow through a horizontal orifice meter installation

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Discharge from a sharp-edged orifice venting to atmosphere — Orifices

A 75 mm sharp-edged orifice in the side of a tank discharges freely to the atmosphere under a head of 2.7 m. With a discharge coefficient of 0.60, compute the theoretical velocity, the actual discharge and the jet's volume delivered in one minute.

Given

  • d=75mmd = 75 mm
  • H=2.7mH = 2.7 m
  • Cd=0.60C_d = 0.60

Find

V_theoretical, Q and the one-minute volume

Start with the thinking

  • Torricelli's result comes straight from Bernoulli with atmospheric pressure on both ends.
  • The discharge coefficient bundles the vena-contracta area reduction with velocity losses.

Step-by-step solution

  1. Formula

    V=2gHV = \sqrt{2gH}
  2. Substituting

    V=(2×9.81×2.7)=7.28m/sV = \sqrt(2\times9.81\times2.7) = 7.28 m/s
  3. Orifice area

    A=π(0.075)2/4=0.00442m2A = \pi(0.075)^{2}/4 = 0.00442 m^{2}
  4. Formula

    Q=CdA2gHQ = C_d A\sqrt{2gH}
  5. Substituting

    Q=0.60(0.00442)(7.28)=0.0193m3/sQ = 0.60(0.00442)(7.28) = 0.0193 m^{3}/s
  6. Volume in 60 s

    ∀=0.0193(60)=1.16m3\forall = 0.0193(60) = 1.16 m^{3}
Answer:
V=7.28m/s,Q=0.0193m3/s(19.3L/s)V = 7.28 m/s, Q = 0.0193 m^{3}/s (19.3 L/s)

Why the other options are there

  • 0.0322 m³/s (C_d ignored)
  • 0.1404 m³/s (square root omitted)

Reference: FE Reference Handbook — Fluid Mechanics → Orifices

Example 2
Discharge from a sharp-edged orifice venting to atmosphere — Orifices (2)

A 75 mm sharp-edged orifice in the side of a tank discharges freely to the atmosphere under a head of 4.5 m. With a discharge coefficient of 0.59, compute the theoretical velocity, the actual discharge and the jet's volume delivered in one minute.

Given

  • d=75mmd = 75 mm
  • H=4.5mH = 4.5 m
  • Cd=0.59C_d = 0.59

Find

V_theoretical, Q and the one-minute volume

Start with the thinking

  • Torricelli's result comes straight from Bernoulli with atmospheric pressure on both ends.
  • The discharge coefficient bundles the vena-contracta area reduction with velocity losses.

Step-by-step solution

  1. Formula

    V=2gHV = \sqrt{2gH}
  2. Substituting

    V=(2×9.81×4.5)=9.40m/sV = \sqrt(2\times9.81\times4.5) = 9.40 m/s
  3. Orifice area

    A=π(0.075)2/4=0.00442m2A = \pi(0.075)^{2}/4 = 0.00442 m^{2}
  4. Formula

    Q=CdA2gHQ = C_d A\sqrt{2gH}
  5. Substituting

    Q=0.59(0.00442)(9.40)=0.0245m3/sQ = 0.59(0.00442)(9.40) = 0.0245 m^{3}/s
  6. Volume in 60 s

    ∀=0.0245(60)=1.47m3\forall = 0.0245(60) = 1.47 m^{3}
Answer:
V=9.40m/s,Q=0.0245m3/s(24.5L/s)V = 9.40 m/s, Q = 0.0245 m^{3}/s (24.5 L/s)

Why the other options are there

  • 0.0415 m³/s (C_d ignored)
  • 0.2301 m³/s (square root omitted)

Reference: FE Reference Handbook — Fluid Mechanics → Orifices

Example 3
Discharge from a sharp-edged orifice venting to atmosphere — Orifices (3)

A 35 mm sharp-edged orifice in the side of a tank discharges freely to the atmosphere under a head of 1.6 m. With a discharge coefficient of 0.61, compute the theoretical velocity, the actual discharge and the jet's volume delivered in one minute.

Given

  • d=35mmd = 35 mm
  • H=1.6mH = 1.6 m
  • Cd=0.61C_d = 0.61

Find

V_theoretical, Q and the one-minute volume

Start with the thinking

  • Torricelli's result comes straight from Bernoulli with atmospheric pressure on both ends.
  • The discharge coefficient bundles the vena-contracta area reduction with velocity losses.

Step-by-step solution

  1. Formula

    V=2gHV = \sqrt{2gH}
  2. Substituting

    V=(2×9.81×1.6)=5.60m/sV = \sqrt(2\times9.81\times1.6) = 5.60 m/s
  3. Orifice area

    A=π(0.035)2/4=0.00096m2A = \pi(0.035)^{2}/4 = 0.00096 m^{2}
  4. Formula

    Q=CdA2gHQ = C_d A\sqrt{2gH}
  5. Substituting

    Q=0.61(0.00096)(5.60)=0.0033m3/sQ = 0.61(0.00096)(5.60) = 0.0033 m^{3}/s
  6. Volume in 60 s

    ∀=0.0033(60)=0.20m3\forall = 0.0033(60) = 0.20 m^{3}
Answer:
V=5.60m/s,Q=0.0033m3/s(3.3L/s)V = 5.60 m/s, Q = 0.0033 m^{3}/s (3.3 L/s)

Why the other options are there

  • 0.0054 m³/s (C_d ignored)
  • 0.0184 m³/s (square root omitted)

Reference: FE Reference Handbook — Fluid Mechanics → Orifices

Example 4
Discharge from a sharp-edged orifice venting to atmosphere — Orifices (4)

A 35 mm sharp-edged orifice in the side of a tank discharges freely to the atmosphere under a head of 4.9 m. With a discharge coefficient of 0.62, compute the theoretical velocity, the actual discharge and the jet's volume delivered in one minute.

Given

  • d=35mmd = 35 mm
  • H=4.9mH = 4.9 m
  • Cd=0.62C_d = 0.62

Find

V_theoretical, Q and the one-minute volume

Start with the thinking

  • Torricelli's result comes straight from Bernoulli with atmospheric pressure on both ends.
  • The discharge coefficient bundles the vena-contracta area reduction with velocity losses.

Step-by-step solution

  1. Formula

    V=2gHV = \sqrt{2gH}
  2. Substituting

    V=(2×9.81×4.9)=9.80m/sV = \sqrt(2\times9.81\times4.9) = 9.80 m/s
  3. Orifice area

    A=π(0.035)2/4=0.00096m2A = \pi(0.035)^{2}/4 = 0.00096 m^{2}
  4. Formula

    Q=CdA2gHQ = C_d A\sqrt{2gH}
  5. Substituting

    Q=0.62(0.00096)(9.80)=0.0058m3/sQ = 0.62(0.00096)(9.80) = 0.0058 m^{3}/s
  6. Volume in 60 s

    ∀=0.0058(60)=0.35m3\forall = 0.0058(60) = 0.35 m^{3}
Answer:
V=9.80m/s,Q=0.0058m3/s(5.8L/s)V = 9.80 m/s, Q = 0.0058 m^{3}/s (5.8 L/s)

Why the other options are there

  • 0.0094 m³/s (C_d ignored)
  • 0.0573 m³/s (square root omitted)

Reference: FE Reference Handbook — Fluid Mechanics → Orifices

Example 5
Discharge from a sharp-edged orifice venting to atmosphere — Orifices (5)

A 70 mm sharp-edged orifice in the side of a tank discharges freely to the atmosphere under a head of 6.2 m. With a discharge coefficient of 0.59, compute the theoretical velocity, the actual discharge and the jet's volume delivered in one minute.

Given

  • d=70mmd = 70 mm
  • H=6.2mH = 6.2 m
  • Cd=0.59C_d = 0.59

Find

V_theoretical, Q and the one-minute volume

Start with the thinking

  • Torricelli's result comes straight from Bernoulli with atmospheric pressure on both ends.
  • The discharge coefficient bundles the vena-contracta area reduction with velocity losses.

Step-by-step solution

  1. Formula

    V=2gHV = \sqrt{2gH}
  2. Substituting

    V=(2×9.81×6.2)=11.03m/sV = \sqrt(2\times9.81\times6.2) = 11.03 m/s
  3. Orifice area

    A=π(0.070)2/4=0.00385m2A = \pi(0.070)^{2}/4 = 0.00385 m^{2}
  4. Formula

    Q=CdA2gHQ = C_d A\sqrt{2gH}
  5. Substituting

    Q=0.59(0.00385)(11.03)=0.0250m3/sQ = 0.59(0.00385)(11.03) = 0.0250 m^{3}/s
  6. Volume in 60 s

    ∀=0.0250(60)=1.50m3\forall = 0.0250(60) = 1.50 m^{3}
Answer:
V=11.03m/s,Q=0.0250m3/s(25.0L/s)V = 11.03 m/s, Q = 0.0250 m^{3}/s (25.0 L/s)

Why the other options are there

  • 0.0424 m³/s (C_d ignored)
  • 0.2762 m³/s (square root omitted)

Reference: FE Reference Handbook — Fluid Mechanics → Orifices

Example 6
Discharge from a sharp-edged orifice venting to atmosphere — Orifices (6)

A 30 mm sharp-edged orifice in the side of a tank discharges freely to the atmosphere under a head of 4.0 m. With a discharge coefficient of 0.65, compute the theoretical velocity, the actual discharge and the jet's volume delivered in one minute.

Given

  • d=30mmd = 30 mm
  • H=4.0mH = 4.0 m
  • Cd=0.65C_d = 0.65

Find

V_theoretical, Q and the one-minute volume

Start with the thinking

  • Torricelli's result comes straight from Bernoulli with atmospheric pressure on both ends.
  • The discharge coefficient bundles the vena-contracta area reduction with velocity losses.

Step-by-step solution

  1. Formula

    V=2gHV = \sqrt{2gH}
  2. Substituting

    V=(2×9.81×4.0)=8.86m/sV = \sqrt(2\times9.81\times4.0) = 8.86 m/s
  3. Orifice area

    A=π(0.030)2/4=0.00071m2A = \pi(0.030)^{2}/4 = 0.00071 m^{2}
  4. Formula

    Q=CdA2gHQ = C_d A\sqrt{2gH}
  5. Substituting

    Q=0.65(0.00071)(8.86)=0.0041m3/sQ = 0.65(0.00071)(8.86) = 0.0041 m^{3}/s
  6. Volume in 60 s

    ∀=0.0041(60)=0.24m3\forall = 0.0041(60) = 0.24 m^{3}
Answer:
V=8.86m/s,Q=0.0041m3/s(4.1L/s)V = 8.86 m/s, Q = 0.0041 m^{3}/s (4.1 L/s)

Why the other options are there

  • 0.0063 m³/s (C_d ignored)
  • 0.0361 m³/s (square root omitted)

Reference: FE Reference Handbook — Fluid Mechanics → Orifices

Example 7
Discharge from a sharp-edged orifice venting to atmosphere — Orifices (7)

A 25 mm sharp-edged orifice in the side of a tank discharges freely to the atmosphere under a head of 3.8 m. With a discharge coefficient of 0.65, compute the theoretical velocity, the actual discharge and the jet's volume delivered in one minute.

Given

  • d=25mmd = 25 mm
  • H=3.8mH = 3.8 m
  • Cd=0.65C_d = 0.65

Find

V_theoretical, Q and the one-minute volume

Start with the thinking

  • Torricelli's result comes straight from Bernoulli with atmospheric pressure on both ends.
  • The discharge coefficient bundles the vena-contracta area reduction with velocity losses.

Step-by-step solution

  1. Formula

    V=2gHV = \sqrt{2gH}
  2. Substituting

    V=(2×9.81×3.8)=8.63m/sV = \sqrt(2\times9.81\times3.8) = 8.63 m/s
  3. Orifice area

    A=π(0.025)2/4=0.00049m2A = \pi(0.025)^{2}/4 = 0.00049 m^{2}
  4. Formula

    Q=CdA2gHQ = C_d A\sqrt{2gH}
  5. Substituting

    Q=0.65(0.00049)(8.63)=0.0028m3/sQ = 0.65(0.00049)(8.63) = 0.0028 m^{3}/s
  6. Volume in 60 s

    ∀=0.0028(60)=0.17m3\forall = 0.0028(60) = 0.17 m^{3}
Answer:
V=8.63m/s,Q=0.0028m3/s(2.8L/s)V = 8.63 m/s, Q = 0.0028 m^{3}/s (2.8 L/s)

Why the other options are there

  • 0.0042 m³/s (C_d ignored)
  • 0.0238 m³/s (square root omitted)

Reference: FE Reference Handbook — Fluid Mechanics → Orifices

Example 8
Discharge from a sharp-edged orifice venting to atmosphere — Orifices (8)

A 95 mm sharp-edged orifice in the side of a tank discharges freely to the atmosphere under a head of 8.3 m. With a discharge coefficient of 0.64, compute the theoretical velocity, the actual discharge and the jet's volume delivered in one minute.

Given

  • d=95mmd = 95 mm
  • H=8.3mH = 8.3 m
  • Cd=0.64C_d = 0.64

Find

V_theoretical, Q and the one-minute volume

Start with the thinking

  • Torricelli's result comes straight from Bernoulli with atmospheric pressure on both ends.
  • The discharge coefficient bundles the vena-contracta area reduction with velocity losses.

Step-by-step solution

  1. Formula

    V=2gHV = \sqrt{2gH}
  2. Substituting

    V=(2×9.81×8.3)=12.76m/sV = \sqrt(2\times9.81\times8.3) = 12.76 m/s
  3. Orifice area

    A=π(0.095)2/4=0.00709m2A = \pi(0.095)^{2}/4 = 0.00709 m^{2}
  4. Formula

    Q=CdA2gHQ = C_d A\sqrt{2gH}
  5. Substituting

    Q=0.64(0.00709)(12.76)=0.0579m3/sQ = 0.64(0.00709)(12.76) = 0.0579 m^{3}/s
  6. Volume in 60 s

    ∀=0.0579(60)=3.47m3\forall = 0.0579(60) = 3.47 m^{3}
Answer:
V=12.76m/s,Q=0.0579m3/s(57.9L/s)V = 12.76 m/s, Q = 0.0579 m^{3}/s (57.9 L/s)

Why the other options are there

  • 0.0905 m³/s (C_d ignored)
  • 0.7387 m³/s (square root omitted)

Reference: FE Reference Handbook — Fluid Mechanics → Orifices

Example 9
Discharge from a sharp-edged orifice venting to atmosphere — Orifices (9)

A 60 mm sharp-edged orifice in the side of a tank discharges freely to the atmosphere under a head of 4.1 m. With a discharge coefficient of 0.64, compute the theoretical velocity, the actual discharge and the jet's volume delivered in one minute.

Given

  • d=60mmd = 60 mm
  • H=4.1mH = 4.1 m
  • Cd=0.64C_d = 0.64

Find

V_theoretical, Q and the one-minute volume

Start with the thinking

  • Torricelli's result comes straight from Bernoulli with atmospheric pressure on both ends.
  • The discharge coefficient bundles the vena-contracta area reduction with velocity losses.

Step-by-step solution

  1. Formula

    V=2gHV = \sqrt{2gH}
  2. Substituting

    V=(2×9.81×4.1)=8.97m/sV = \sqrt(2\times9.81\times4.1) = 8.97 m/s
  3. Orifice area

    A=π(0.060)2/4=0.00283m2A = \pi(0.060)^{2}/4 = 0.00283 m^{2}
  4. Formula

    Q=CdA2gHQ = C_d A\sqrt{2gH}
  5. Substituting

    Q=0.64(0.00283)(8.97)=0.0162m3/sQ = 0.64(0.00283)(8.97) = 0.0162 m^{3}/s
  6. Volume in 60 s

    ∀=0.0162(60)=0.97m3\forall = 0.0162(60) = 0.97 m^{3}
Answer:
V=8.97m/s,Q=0.0162m3/s(16.2L/s)V = 8.97 m/s, Q = 0.0162 m^{3}/s (16.2 L/s)

Why the other options are there

  • 0.0254 m³/s (C_d ignored)
  • 0.1456 m³/s (square root omitted)

Reference: FE Reference Handbook — Fluid Mechanics → Orifices

Example 10
Discharge from a sharp-edged orifice venting to atmosphere — Orifices (10)

A 95 mm sharp-edged orifice in the side of a tank discharges freely to the atmosphere under a head of 4.0 m. With a discharge coefficient of 0.65, compute the theoretical velocity, the actual discharge and the jet's volume delivered in one minute.

Given

  • d=95mmd = 95 mm
  • H=4.0mH = 4.0 m
  • Cd=0.65C_d = 0.65

Find

V_theoretical, Q and the one-minute volume

Start with the thinking

  • Torricelli's result comes straight from Bernoulli with atmospheric pressure on both ends.
  • The discharge coefficient bundles the vena-contracta area reduction with velocity losses.

Step-by-step solution

  1. Formula

    V=2gHV = \sqrt{2gH}
  2. Substituting

    V=(2×9.81×4.0)=8.86m/sV = \sqrt(2\times9.81\times4.0) = 8.86 m/s
  3. Orifice area

    A=π(0.095)2/4=0.00709m2A = \pi(0.095)^{2}/4 = 0.00709 m^{2}
  4. Formula

    Q=CdA2gHQ = C_d A\sqrt{2gH}
  5. Substituting

    Q=0.65(0.00709)(8.86)=0.0408m3/sQ = 0.65(0.00709)(8.86) = 0.0408 m^{3}/s
  6. Volume in 60 s

    ∀=0.0408(60)=2.45m3\forall = 0.0408(60) = 2.45 m^{3}
Answer:
V=8.86m/s,Q=0.0408m3/s(40.8L/s)V = 8.86 m/s, Q = 0.0408 m^{3}/s (40.8 L/s)

Why the other options are there

  • 0.0628 m³/s (C_d ignored)
  • 0.3616 m³/s (square root omitted)

Reference: FE Reference Handbook — Fluid Mechanics → Orifices

© 2026 Dr. Steve Efe. Civil Engineering Capstone Studio. All rights reserved.