Questions and Answers
What must the driver/operator note before any pump discharges are opened?
What factor is squared when determining the residual pressure after adding additional lines?
If a second 250 gpm line is added to a system with an intake pressure drop to 52 psi, what is the resultant pressure drop if the original drop was 8 psi?
When time to adjust the flow rate is critical, what method is useful for quick calculations?
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At what pressure should the residual pressure ideally be maintained to avoid performance issues?
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What is the additional water available when there is a 12% decrease in pumper intake pressure?
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If the static pressure is 80 psi and the residual pressure is 72 psi, how many additional lines of equal flow may be added?
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What is the primary limitation of the first-digit method for calculating available water?
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Using the first-digit method, if the first digit of the static pressure is 5 and the psi drop is 9, how many additional lines can be added?
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When there is a 25% or greater decrease in pumper intake pressure, what can be inferred about additional water availability?
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How do you determine the additional lines using the first-digit method?
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If a pumper delivers 500 gpm with a static pressure of 55 psi, what would be the additional lines if the residual pressure is 53 psi?
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What effect does a psi drop greater than the static pressure's first digit multiplied by three have on additional flow lines?
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What is the formula used to calculate the percent drop in pressure?
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If the percent drop is calculated to be 16%, how many additional lines can be added?
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Given a static pressure of 500 kPa and a residual pressure of 450 kPa, what is the percent drop?
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What is indicated when the percent drop from a hydrant exceeds 25%?
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In Example 10.1, if the static pressure is 70 psi and the residual is 63 psi, how many gpm can be theoretically supported by the hydrant?
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If a pumper supplies one line at 1000 L/min and the residual pressure is 450 kPa, what action should be taken if the static pressure reads 600 kPa?
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Which of the following statements about the percentage method is incorrect?
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What is the significance of Table 10.1 in the context of hydrant water availability?
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What happens to the pressure drop in the system when the flow rate is doubled?
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What is the pressure drop in the system if the original pressure drop is 55 kPa after adding a second line?
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What should be done to the engine RPMs when shutting down the water supply operation?
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What can water hammer potentially damage in the water supply system?
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Why should valves be closed in a slow and smooth motion during shutdown?
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What is the assumed flow rate for a 2 ½ inch (65 mm) hose?
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How is the multiplication factor determined when evaluating pressure drop with additional lines?
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What is the advisable residual pressure in the system for adding additional hoselines?
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Study Notes
Percentage Method
- Calculate drop in pressure with the formula: Percent Drop = (Static - Residual)(100) / Static.
- Percentage drops indicate available water from hydrants:
- 10% or less: add three additional hoselines with the same flow.
- 11-15%: add two additional hoselines.
- 16-25%: add one additional hoseline.
- Over 25%: potentially more water available, but less than current flow.
- Example for a flow of 250 gpm:
- Static: 70 psi, Residual: 63 psi.
- Percent Drop = (70 - 63)(100) / 70 = 10%.
- Three additional lines can be added.
- Example for a flow of 1,000 L/min:
- Static: 500 kPa, Residual: 450 kPa.
- Percent Drop = (500 - 450)(100) / 500 = 10%.
- Three additional lines can be added.
First-Digit Method
- Quick calculation method using static pressure in psi only.
- Steps to determine additional lines:
- Calculate the difference in psi: Static - Residual.
- First digit of static pressure dictates potential extra lines:
- If the psi drop ≤ (first digit) x 1: add three lines.
- If ≤ (first digit) x 2: add two lines.
- If ≤ (first digit) x 3: add one line.
- Example: Static 65 psi, Residual 58 psi, Difference = 7 psi.
- First digit: 6, thus 6 x 1 = 6.
- 7 psi is greater than 6 but less than 12, so two more lines can be added.
Squaring-the-Lines Method
- Utilizes static pressure for calculations with multiple hoselines.
- Key table for flow rates per hose size:
- 1½ inch (38 mm): 125 gpm (500 L/min)
- 1¾ inch (45 mm): 175 gpm (700 L/min)
- 2 inch (50 mm): 200 gpm (800 L/min)
- 2½ inch (65 mm): 250 gpm (1,000 L/min)
- When adding a line, use the formula: Multiplication Factor = (Number of Lines)².
- Example: Adding a second 1,000 L/min line results in:
- Multiplication Factor = 2² = 4.
- Resultant pressure drop: Original drop x 4.
- Important note: Each flow doubling results in quadrupled pressure drop.
Shutting Down the Hydrant Operation
- Slow and smooth flow adjustments help prevent water hammer and pressure surges.
- Water hammer can damage hydrants and plumbing systems.
- Recommended procedure:
- Gradually decrease engine RPMs to idle.
- Discontinue any pressure control devices.
- Close valves smoothly.
- Disengage pump before closing hydrant valves.
- Close hydrant with slow and steady motion to prevent system damage.
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Description
This quiz explores the percentage method for calculating water availability from hydrants. Using a specific formula, it helps determine the drop in pressure and how many additional hoselines can be supplied based on the available water. Test your understanding of this important fire service calculation.
