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Fire Sprinkler Discharge

Hydraulics · FE Reference Handbook section

Hydraulics
4 formulas
10 exam-style examples
~53 min
All Hydraulics lectures

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
Sprinkler discharge from the K factor — solve for discharge — Fire Sprinkler Discharge

a pendent sprinkler on a warehouse branch line Given sprinkler K factor (K) = 10.3000 gpm/psi^0.5; residual pressure at the head (P) = 63.0000 psi, determine the discharge (Q) in gpm.

Given

  • sprinklerKfactor(K)=10.3000gpm/psi0.5sprinkler K factor (K) = 10.3000 gpm/psi^0.5
  • residualpressureatthehead(P)=63.0000psiresidual pressure at the head (P) = 63.0000 psi

Find

discharge (Q), in gpm

Start with the thinking

  • The governing relation printed in this handbook section is Sprinkler discharge from the K factor.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A fire-protection sprinkler head discharges under the residual pressure at the head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=KPQ = K \sqrt{P}
  2. Step 2 — Rearrange symbolically for Q:

    Q=KPQ = K \sqrt{P}
  3. Step 3 — List the givens: sprinkler K factor (K) = 10.3000 gpm/psi^0.5, residual pressure at the head (P) = 63.0000 psi.

  4. Step 4 — Substitute the given values:

    Q=10.300063.0000Q = 10.3000 \sqrt{63.0000}
  5. Step 5 — Evaluate:

    Q=81.7537 gpmQ = 81.7537\ \text{gpm}
  6. Step 6 — Check: returning Q = 81.7537 gpm to

    Q=KPQ = K \sqrt{P}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q=81.7537 gpmQ = 81.7537\ \text{gpm}

Why the other options are there

  • 163.5 — kept a factor of two that cancels in the correct rearrangement.
  • 40.8769 — dropped that same factor in the other direction.
  • 89.9291 — rounded an intermediate value before the final step.

Reference: FE Handbook — Sprinkler K Factors

Example 2
Sprinkler discharge from the K factor — solve for sprinkler K factor — Fire Sprinkler Discharge (2)

an upright sprinkler protecting a parking structure Given discharge (Q) = 106.6 gpm; residual pressure at the head (P) = 37.5000 psi, determine the sprinkler K factor (K) in gpm/psi^0.5.

Given

  • discharge(Q)=106.6gpmdischarge (Q) = 106.6 gpm
  • residualpressureatthehead(P)=37.5000psiresidual pressure at the head (P) = 37.5000 psi

Find

sprinkler K factor (K), in gpm/psi^0.5

Start with the thinking

  • The governing relation printed in this handbook section is Sprinkler discharge from the K factor.
  • Everything except K is given, so isolate K symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A fire-protection sprinkler head discharges under the residual pressure at the head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=KPQ = K \sqrt{P}
  2. Step 2 — Rearrange symbolically for K:

    K=QPK = \dfrac{Q}{\sqrt{P}}
  3. Step 3

    Listthegivens:discharge(Q)=106.6gpm,residualpressureatthehead(P)=37.5000psiList the givens: discharge (Q) = 106.6 gpm, residual pressure at the head (P) = 37.5000 psi
  4. Step 4 — Substitute the given values:

    K=106.637.5000K = \dfrac{106.6}{\sqrt{37.5000}}
  5. Step 5 — Evaluate:

    K = 17.4077\ \text{gpm/psi^0.5}
  6. Step 6 — Check: returning K = 17.4077 gpm/psi^0.5 to

    Q=KPQ = K \sqrt{P}

    reproduces the given quantities, and both sides carry the same units.

Answer:
K = 17.4077\ \text{gpm/psi^0.5}

Why the other options are there

  • 34.8154 — kept a factor of two that cancels in the correct rearrangement.
  • 8.7039 — dropped that same factor in the other direction.
  • 19.1485 — rounded an intermediate value before the final step.

Reference: FE Handbook — Sprinkler K Factors

Example 3
Sprinkler discharge from the K factor — solve for residual pressure at the head — Fire Sprinkler Discharge (3)

a sidewall sprinkler on a corridor main Given discharge (Q) = 134.9 gpm; sprinkler K factor (K) = 13.5000 gpm/psi^0.5, determine the residual pressure at the head (P) in psi.

Given

  • discharge(Q)=134.9gpmdischarge (Q) = 134.9 gpm
  • sprinklerKfactor(K)=13.5000gpm/psi0.5sprinkler K factor (K) = 13.5000 gpm/psi^0.5

Find

residual pressure at the head (P), in psi

Start with the thinking

  • The governing relation printed in this handbook section is Sprinkler discharge from the K factor.
  • Everything except P is given, so isolate P symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A fire-protection sprinkler head discharges under the residual pressure at the head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=KPQ = K \sqrt{P}
  2. Step 2 — Rearrange symbolically for P:

    P=(QK)2P = \left(\dfrac{Q}{K}\right)^2
  3. Step 3

    Listthegivens:discharge(Q)=134.9gpm,sprinklerKfactor(K)=13.5000gpm/psi0.5List the givens: discharge (Q) = 134.9 gpm, sprinkler K factor (K) = 13.5000 gpm/psi^0.5
  4. Step 4 — Substitute the given values:

    P=(134.913.5000)2P = \left(\dfrac{134.9}{13.5000}\right)^2
  5. Step 5 — Evaluate:

    P=99.8519 psiP = 99.8519\ \text{psi}
  6. Step 6 — Check: returning P = 99.8519 psi to

    Q=KPQ = K \sqrt{P}

    reproduces the given quantities, and both sides carry the same units.

Answer:
P=99.8519 psiP = 99.8519\ \text{psi}

Why the other options are there

  • 199.7 — kept a factor of two that cancels in the correct rearrangement.
  • 49.9260 — dropped that same factor in the other direction.
  • 109.8 — rounded an intermediate value before the final step.

Reference: FE Handbook — Sprinkler K Factors

Example 4
Sprinkler discharge from the K factor — solve for discharge (case 2) — Fire Sprinkler Discharge (4)

a pendent sprinkler on a warehouse branch line Given sprinkler K factor (K) = 5.7000 gpm/psi^0.5; residual pressure at the head (P) = 18.5000 psi, determine the discharge (Q) in gpm.

Given

  • sprinklerKfactor(K)=5.7000gpm/psi0.5sprinkler K factor (K) = 5.7000 gpm/psi^0.5
  • residualpressureatthehead(P)=18.5000psiresidual pressure at the head (P) = 18.5000 psi

Find

discharge (Q), in gpm

Start with the thinking

  • The governing relation printed in this handbook section is Sprinkler discharge from the K factor.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A fire-protection sprinkler head discharges under the residual pressure at the head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=KPQ = K \sqrt{P}
  2. Step 2 — Rearrange symbolically for Q:

    Q=KPQ = K \sqrt{P}
  3. Step 3 — List the givens: sprinkler K factor (K) = 5.7000 gpm/psi^0.5, residual pressure at the head (P) = 18.5000 psi.

  4. Step 4 — Substitute the given values:

    Q=5.700018.5000Q = 5.7000 \sqrt{18.5000}
  5. Step 5 — Evaluate:

    Q=24.5166 gpmQ = 24.5166\ \text{gpm}
  6. Step 6 — Check: returning Q = 24.5166 gpm to

    Q=KPQ = K \sqrt{P}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q=24.5166 gpmQ = 24.5166\ \text{gpm}

Why the other options are there

  • 49.0333 — kept a factor of two that cancels in the correct rearrangement.
  • 12.2583 — dropped that same factor in the other direction.
  • 26.9683 — rounded an intermediate value before the final step.

Reference: FE Handbook — Sprinkler K Factors

Example 5
Sprinkler discharge from the K factor — solve for sprinkler K factor (case 2) — Fire Sprinkler Discharge (5)

an upright sprinkler protecting a parking structure Given discharge (Q) = 181.5 gpm; residual pressure at the head (P) = 67.5000 psi, determine the sprinkler K factor (K) in gpm/psi^0.5.

Given

  • discharge(Q)=181.5gpmdischarge (Q) = 181.5 gpm
  • residualpressureatthehead(P)=67.5000psiresidual pressure at the head (P) = 67.5000 psi

Find

sprinkler K factor (K), in gpm/psi^0.5

Start with the thinking

  • The governing relation printed in this handbook section is Sprinkler discharge from the K factor.
  • Everything except K is given, so isolate K symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A fire-protection sprinkler head discharges under the residual pressure at the head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=KPQ = K \sqrt{P}
  2. Step 2 — Rearrange symbolically for K:

    K=QPK = \dfrac{Q}{\sqrt{P}}
  3. Step 3

    Listthegivens:discharge(Q)=181.5gpm,residualpressureatthehead(P)=67.5000psiList the givens: discharge (Q) = 181.5 gpm, residual pressure at the head (P) = 67.5000 psi
  4. Step 4 — Substitute the given values:

    K=181.567.5000K = \dfrac{181.5}{\sqrt{67.5000}}
  5. Step 5 — Evaluate:

    K = 22.0915\ \text{gpm/psi^0.5}
  6. Step 6 — Check: returning K = 22.0915 gpm/psi^0.5 to

    Q=KPQ = K \sqrt{P}

    reproduces the given quantities, and both sides carry the same units.

Answer:
K = 22.0915\ \text{gpm/psi^0.5}

Why the other options are there

  • 44.1830 — kept a factor of two that cancels in the correct rearrangement.
  • 11.0457 — dropped that same factor in the other direction.
  • 24.3006 — rounded an intermediate value before the final step.

Reference: FE Handbook — Sprinkler K Factors

Example 6
Sprinkler discharge from the K factor — solve for residual pressure at the head (case 2) — Fire Sprinkler Discharge (6)

a sidewall sprinkler on a corridor main Given discharge (Q) = 37.7000 gpm; sprinkler K factor (K) = 6.2000 gpm/psi^0.5, determine the residual pressure at the head (P) in psi.

Given

  • discharge(Q)=37.7000gpmdischarge (Q) = 37.7000 gpm
  • sprinklerKfactor(K)=6.2000gpm/psi0.5sprinkler K factor (K) = 6.2000 gpm/psi^0.5

Find

residual pressure at the head (P), in psi

Start with the thinking

  • The governing relation printed in this handbook section is Sprinkler discharge from the K factor.
  • Everything except P is given, so isolate P symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A fire-protection sprinkler head discharges under the residual pressure at the head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=KPQ = K \sqrt{P}
  2. Step 2 — Rearrange symbolically for P:

    P=(QK)2P = \left(\dfrac{Q}{K}\right)^2
  3. Step 3

    Listthegivens:discharge(Q)=37.7000gpm,sprinklerKfactor(K)=6.2000gpm/psi0.5List the givens: discharge (Q) = 37.7000 gpm, sprinkler K factor (K) = 6.2000 gpm/psi^0.5
  4. Step 4 — Substitute the given values:

    P=(37.70006.2000)2P = \left(\dfrac{37.7000}{6.2000}\right)^2
  5. Step 5 — Evaluate:

    P=36.9742 psiP = 36.9742\ \text{psi}
  6. Step 6 — Check: returning P = 36.9742 psi to

    Q=KPQ = K \sqrt{P}

    reproduces the given quantities, and both sides carry the same units.

Answer:
P=36.9742 psiP = 36.9742\ \text{psi}

Why the other options are there

  • 73.9485 — kept a factor of two that cancels in the correct rearrangement.
  • 18.4871 — dropped that same factor in the other direction.
  • 40.6717 — rounded an intermediate value before the final step.

Reference: FE Handbook — Sprinkler K Factors

Example 7
Sprinkler discharge from the K factor — solve for discharge (case 3) — Fire Sprinkler Discharge (7)

a pendent sprinkler on a warehouse branch line Given sprinkler K factor (K) = 6.3000 gpm/psi^0.5; residual pressure at the head (P) = 88.5000 psi, determine the discharge (Q) in gpm.

Given

  • sprinklerKfactor(K)=6.3000gpm/psi0.5sprinkler K factor (K) = 6.3000 gpm/psi^0.5
  • residualpressureatthehead(P)=88.5000psiresidual pressure at the head (P) = 88.5000 psi

Find

discharge (Q), in gpm

Start with the thinking

  • The governing relation printed in this handbook section is Sprinkler discharge from the K factor.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A fire-protection sprinkler head discharges under the residual pressure at the head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=KPQ = K \sqrt{P}
  2. Step 2 — Rearrange symbolically for Q:

    Q=KPQ = K \sqrt{P}
  3. Step 3 — List the givens: sprinkler K factor (K) = 6.3000 gpm/psi^0.5, residual pressure at the head (P) = 88.5000 psi.

  4. Step 4 — Substitute the given values:

    Q=6.300088.5000Q = 6.3000 \sqrt{88.5000}
  5. Step 5 — Evaluate:

    Q=59.2669 gpmQ = 59.2669\ \text{gpm}
  6. Step 6 — Check: returning Q = 59.2669 gpm to

    Q=KPQ = K \sqrt{P}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q=59.2669 gpmQ = 59.2669\ \text{gpm}

Why the other options are there

  • 118.5 — kept a factor of two that cancels in the correct rearrangement.
  • 29.6334 — dropped that same factor in the other direction.
  • 65.1936 — rounded an intermediate value before the final step.

Reference: FE Handbook — Sprinkler K Factors

Example 8
Sprinkler discharge from the K factor — solve for sprinkler K factor (case 3) — Fire Sprinkler Discharge (8)

an upright sprinkler protecting a parking structure Given discharge (Q) = 178.9 gpm; residual pressure at the head (P) = 53.5000 psi, determine the sprinkler K factor (K) in gpm/psi^0.5.

Given

  • discharge(Q)=178.9gpmdischarge (Q) = 178.9 gpm
  • residualpressureatthehead(P)=53.5000psiresidual pressure at the head (P) = 53.5000 psi

Find

sprinkler K factor (K), in gpm/psi^0.5

Start with the thinking

  • The governing relation printed in this handbook section is Sprinkler discharge from the K factor.
  • Everything except K is given, so isolate K symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A fire-protection sprinkler head discharges under the residual pressure at the head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=KPQ = K \sqrt{P}
  2. Step 2 — Rearrange symbolically for K:

    K=QPK = \dfrac{Q}{\sqrt{P}}
  3. Step 3

    Listthegivens:discharge(Q)=178.9gpm,residualpressureatthehead(P)=53.5000psiList the givens: discharge (Q) = 178.9 gpm, residual pressure at the head (P) = 53.5000 psi
  4. Step 4 — Substitute the given values:

    K=178.953.5000K = \dfrac{178.9}{\sqrt{53.5000}}
  5. Step 5 — Evaluate:

    K = 24.4587\ \text{gpm/psi^0.5}
  6. Step 6 — Check: returning K = 24.4587 gpm/psi^0.5 to

    Q=KPQ = K \sqrt{P}

    reproduces the given quantities, and both sides carry the same units.

Answer:
K = 24.4587\ \text{gpm/psi^0.5}

Why the other options are there

  • 48.9174 — kept a factor of two that cancels in the correct rearrangement.
  • 12.2294 — dropped that same factor in the other direction.
  • 26.9046 — rounded an intermediate value before the final step.

Reference: FE Handbook — Sprinkler K Factors

Example 9
Sprinkler discharge from the K factor — solve for residual pressure at the head (case 3) — Fire Sprinkler Discharge (9)

a sidewall sprinkler on a corridor main Given discharge (Q) = 98.3000 gpm; sprinkler K factor (K) = 8.6000 gpm/psi^0.5, determine the residual pressure at the head (P) in psi.

Given

  • discharge(Q)=98.3000gpmdischarge (Q) = 98.3000 gpm
  • sprinklerKfactor(K)=8.6000gpm/psi0.5sprinkler K factor (K) = 8.6000 gpm/psi^0.5

Find

residual pressure at the head (P), in psi

Start with the thinking

  • The governing relation printed in this handbook section is Sprinkler discharge from the K factor.
  • Everything except P is given, so isolate P symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A fire-protection sprinkler head discharges under the residual pressure at the head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=KPQ = K \sqrt{P}
  2. Step 2 — Rearrange symbolically for P:

    P=(QK)2P = \left(\dfrac{Q}{K}\right)^2
  3. Step 3

    Listthegivens:discharge(Q)=98.3000gpm,sprinklerKfactor(K)=8.6000gpm/psi0.5List the givens: discharge (Q) = 98.3000 gpm, sprinkler K factor (K) = 8.6000 gpm/psi^0.5
  4. Step 4 — Substitute the given values:

    P=(98.30008.6000)2P = \left(\dfrac{98.3000}{8.6000}\right)^2
  5. Step 5 — Evaluate:

    P=130.7 psiP = 130.7\ \text{psi}
  6. Step 6 — Check: returning P = 130.7 psi to

    Q=KPQ = K \sqrt{P}

    reproduces the given quantities, and both sides carry the same units.

Answer:
P=130.7 psiP = 130.7\ \text{psi}

Why the other options are there

  • 261.3 — kept a factor of two that cancels in the correct rearrangement.
  • 65.3251 — dropped that same factor in the other direction.
  • 143.7 — rounded an intermediate value before the final step.

Reference: FE Handbook — Sprinkler K Factors

Example 10
Sprinkler discharge from the K factor — solve for discharge (case 4) — Fire Sprinkler Discharge (10)

a pendent sprinkler on a warehouse branch line Given sprinkler K factor (K) = 12.7000 gpm/psi^0.5; residual pressure at the head (P) = 14.0000 psi, determine the discharge (Q) in gpm.

Given

  • sprinklerKfactor(K)=12.7000gpm/psi0.5sprinkler K factor (K) = 12.7000 gpm/psi^0.5
  • residualpressureatthehead(P)=14.0000psiresidual pressure at the head (P) = 14.0000 psi

Find

discharge (Q), in gpm

Start with the thinking

  • The governing relation printed in this handbook section is Sprinkler discharge from the K factor.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • A fire-protection sprinkler head discharges under the residual pressure at the head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=KPQ = K \sqrt{P}
  2. Step 2 — Rearrange symbolically for Q:

    Q=KPQ = K \sqrt{P}
  3. Step 3 — List the givens: sprinkler K factor (K) = 12.7000 gpm/psi^0.5, residual pressure at the head (P) = 14.0000 psi.

  4. Step 4 — Substitute the given values:

    Q=12.700014.0000Q = 12.7000 \sqrt{14.0000}
  5. Step 5 — Evaluate:

    Q=47.5190 gpmQ = 47.5190\ \text{gpm}
  6. Step 6 — Check: returning Q = 47.5190 gpm to

    Q=KPQ = K \sqrt{P}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q=47.5190 gpmQ = 47.5190\ \text{gpm}

Why the other options are there

  • 95.0381 — kept a factor of two that cancels in the correct rearrangement.
  • 23.7595 — dropped that same factor in the other direction.
  • 52.2710 — rounded an intermediate value before the final step.

Reference: FE Handbook — Sprinkler K Factors

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