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OK Fire Sprinkler practice questions

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Question 1Codes, Standards, and Licensing Administration

Which NFPA document is the primary standard for designing and installing automatic fire sprinkler systems in commercial and industrial occupancies?

  1. NFPA 13R
  2. NFPA 13D
  3. NFPA 13 Correct answer.
  4. NFPA 14

Explanation

NFPA 13 is the design and installation standard for commercial, industrial, and other nonresidential sprinkler systems. NFPA 13R and 13D cover limited residential applications, and NFPA 14 addresses standpipe systems.

Question 2Codes, Standards, and Licensing Administration

In Oklahoma, which state entity administers the fire sprinkler contractor licensing program?

  1. The Oklahoma Department of Health
  2. The Oklahoma Corporation Commission
  3. The Oklahoma Department of Labor
  4. The Oklahoma State Fire Marshal Correct answer.

Explanation

The Oklahoma Fire Sprinkler Contractors Act places licensing and enforcement with the State Fire Marshal. That office issues contractor and individual licenses and investigates complaints.

Question 3Codes, Standards, and Licensing Administration

Before installing a new fire sprinkler system in a commercial building, the contractor must submit working plans to which party for review and approval?

  1. The National Fire Protection Association
  2. The sprinkler manufacturer
  3. The local water utility
  4. The authority having jurisdiction Correct answer.

Explanation

The authority having jurisdiction reviews and approves working plans for code compliance before installation begins. Water utilities, NFPA, and manufacturers do not perform the required regulatory plan approval.

Question 4Codes, Standards, and Licensing Administration

NFPA 13R is limited to residential occupancies of what maximum height?

  1. Any height, if the system is hydraulically calculated
  2. Up to and including six stories
  3. Only single-story buildings
  4. Up to and including four stories Correct answer.

Explanation

NFPA 13R permits a reduced residential design for occupancies up to and including four stories. Buildings exceeding that height generally require NFPA 13 design.

Question 5Codes, Standards, and Licensing Administration

Under NFPA 25, gauges on a wet-pipe sprinkler system must be inspected at which frequency?

  1. Quarterly
  2. Weekly
  3. Monthly Correct answer.
  4. Annually

Explanation

NFPA 25 requires monthly inspection of system gauges to confirm normal water supply pressure. Quarterly and annual frequencies apply to other components and tests, not routine gauge inspection.

Question 6Codes, Standards, and Licensing Administration

Which item is typically required to obtain and maintain an Oklahoma fire sprinkler contractor license?

  1. General liability insurance and a surety bond Correct answer.
  2. Membership in the National Fire Protection Association
  3. NICET Level IV certification for every employee
  4. Affiliation with a recognized labor union

Explanation

Oklahoma licensing rules require the contractor to demonstrate financial responsibility through liability insurance and bonding. NFPA membership, union affiliation, and universal NICET Level IV certification are not general license conditions.

Question 7Codes, Standards, and Licensing Administration

Working plans for a fire sprinkler system must be prepared by which party?

  1. The local water utility
  2. Any licensed electrical contractor
  3. The building owner without technical review
  4. A person acceptable to the AHJ who is knowledgeable in sprinkler design Correct answer.

Explanation

NFPA 13 requires working plans to be prepared by a person competent in sprinkler system layout and acceptable to the AHJ. Electrical licensure, utility ownership, or building ownership alone does not satisfy that requirement.

Question 8Codes, Standards, and Licensing Administration

NFPA 13D is intended for which type of occupancy?

  1. Storage warehouses
  2. High-rise office buildings
  3. Commercial cooking areas
  4. One- and two-family dwellings and manufactured homes Correct answer.

Explanation

NFPA 13D provides a life-safety-oriented standard for one- and two-family dwellings and manufactured homes. Commercial, storage, and high-rise occupancies fall under NFPA 13 or other applicable standards.

Question 9Codes, Standards, and Licensing Administration

A jurisdiction has adopted NFPA 13 by reference without amendments. A contractor proposes a detail that follows the manufacturer's instructions but conflicts with NFPA 13. Which document governs?

  1. The adopted NFPA 13 standard Correct answer.
  2. The water utility's preference
  3. The contractor's professional judgment
  4. The manufacturer's instructions in all cases

Explanation

Once a standard is adopted by reference, it becomes enforceable law for that jurisdiction and controls over conflicting manufacturer instructions. A manufacturer may seek an alternative-means approval, but the adopted code is the baseline.

Question 10Codes, Standards, and Licensing Administration

Which submittal deficiency would most likely cause an AHJ to reject fire sprinkler working plans?

  1. Showing sprinkler spacing on the drawings
  2. Missing hydraulic calculations Correct answer.
  3. Use of NFPA 13 as the design standard
  4. Inclusion of a water supply curve

Explanation

NFPA 13 requires hydraulic calculations to show that the available water supply meets system demand. A water supply curve, correct standard reference, and sprinkler spacing are normal and expected submittal elements.

Question 11Codes, Standards, and Licensing Administration

NFPA 13 requires newly installed aboveground sprinkler piping to be hydrostatically tested at which pressure and duration where the normal working pressure does not exceed 150 psi?

  1. 200 psi for two hours Correct answer.
  2. 150 psi for two hours
  3. 100 psi for one hour
  4. 250 psi for one hour

Explanation

NFPA 13 requires a hydrostatic test of 200 psi held for two hours for new aboveground piping when system working pressure is 150 psi or less; where working pressure exceeds 150 psi, the test pressure is 50 psi above working pressure. The test must be witnessed and documented before the system is placed in service.

Question 12Codes, Standards, and Licensing Administration

Under NFPA 25, a main drain flow test on a wet-pipe sprinkler system is required at which frequency?

  1. Annually Correct answer.
  2. Quarterly
  3. Every five years
  4. Monthly

Explanation

NFPA 25 requires an annual main drain flow test for wet-pipe systems to confirm that the water supply valve is fully open and that the supply piping is unobstructed. The test must also be repeated after any mainline valve has been closed and reopened, since the recorded static and residual pressures reveal a partially closed valve.

Question 13Codes, Standards, and Licensing Administration

Under NFPA 25, who is responsible for ensuring that an installed sprinkler system is inspected, tested, and maintained in accordance with the standard?

  1. The authority having jurisdiction
  2. The property insurer
  3. The installing contractor
  4. The owner or its designee Correct answer.

Explanation

NFPA 25 places the inspection, testing, and maintenance obligation on the owner, who may assign the work to a designated representative such as a maintenance supervisor or a service contractor. The AHJ enforces the standard and the insurer may require evidence of compliance, but neither carries the operating responsibility.

Question 14Codes, Standards, and Licensing Administration

At the completion of a new sprinkler installation, which document must the installing contractor complete and furnish to the owner and the authority having jurisdiction to record acceptance test results?

  1. An NFPA 25 annual inspection report
  2. A manufacturer's data sheet for each sprinkler head
  3. A water utility statement of available flow
  4. The Contractor's Material and Test Certificate Correct answer.

Explanation

NFPA 13 requires the installing contractor to complete the Contractor's Material and Test Certificate for underground and aboveground piping, recording hydrostatic and flow test results, and to deliver it to the owner and AHJ. The certificate documents that the as-built system passed the required acceptance tests before being placed in service.

Question 15Codes, Standards, and Licensing Administration

A wet-pipe system serving an occupied nursing home must be shut down for repairs expected to take 14 hours. Under NFPA 25, what is required beyond notifying the AHJ, fire department, and insurer?

  1. A fire watch or approved impairment program is implemented Correct answer.
  2. The system is drained and tagged out of service for the duration
  3. The building is evacuated and left unoccupied until restored
  4. Nothing further, because impairments under 24 hours need no action

Explanation

NFPA 25 requires that where a sprinkler system is impaired for more than 10 hours in an occupied building, the owner implement a fire watch or an approved impairment program until protection is restored. Notification alone is insufficient; the compensating measure must be in place and documented.

Question 16Codes, Standards, and Licensing Administration

Under NFPA 25, an electric-driven fire pump supplying a sprinkler system must be run at no-flow (churn) conditions at what minimum frequency?

  1. Weekly Correct answer.
  2. Annually
  3. Monthly
  4. Daily

Explanation

NFPA 25 requires fire pumps to be run weekly at churn, with no water flowing, for a minimum of 10 minutes to confirm the controller, driver, and pump operate properly. Monthly attention is given to other items such as a visual inspection of the pump house and checking the controller indicators.

Question 17Codes, Standards, and Licensing Administration

A plan reviewer is checking the water supply demand shown on hydraulic calculations for a new light hazard system. Besides sprinkler flow at the remote area, the demand must include which additional quantity?

  1. The hose stream allowance for the occupancy Correct answer.
  2. A flat 10 percent safety factor on all systems
  3. The domestic water demand only
  4. The fire pump churn pressure as additional flow

Explanation

NFPA 13 requires the water supply demand to combine sprinkler flow at the base of the riser with the hose stream allowance for the occupancy classification. Omitting the hose stream allowance understates the demand and is a common reason for rejecting hydraulic calculations during plan review.

Question 18Codes, Standards, and Licensing Administration

During a rough-in inspection, an installer has positioned upright sprinkler deflectors 18 inches below a smooth, flat ceiling. To comply with NFPA 13, the deflectors must be repositioned into which range below the ceiling?

  1. 6 inches to 12 inches
  2. 1 inch to 12 inches Correct answer.
  3. 2 inches to 6 inches
  4. 4 inches to 18 inches

Explanation

NFPA 13 requires standard spray sprinkler deflectors under a smooth, flat ceiling to be positioned from 1 inch to 12 inches below the ceiling, with the specific distance set by the sprinkler's listing. A deflector at 18 inches is outside that range and would delay sprinkler activation and distort the discharge pattern.

Question 19Codes, Standards, and Licensing Administration

A hydraulically calculated dry-pipe system is designed using the density/area method. Compared with a wet-pipe system using the same density and the same remote area, how must the remote area be adjusted for the dry-pipe system?

  1. Increased by 30 percent Correct answer.
  2. Increased by 10 percent
  3. Reduced by 25 percent
  4. No adjustment is required

Explanation

NFPA 13 requires the remote area of a dry-pipe system to be increased by 30 percent because air must be expelled before water reaches the remote sprinklers, delaying application. The larger area accounts for the additional water that flows while the system is filling.

Question 20Codes, Standards, and Licensing Administration

Using the density/area method for a light hazard wet-pipe system, a designer's curve reading suggests a remote area of 1,200 sq ft. What is the minimum remote area NFPA 13 permits for this design?

  1. 1,200 sq ft
  2. 3,000 sq ft
  3. 1,500 sq ft Correct answer.
  4. 2,000 sq ft

Explanation

NFPA 13 does not permit the density/area method remote area for a light hazard wet-pipe system to fall below 1,500 sq ft, regardless of what a curve extrapolation suggests. The floor exists so that the calculation reflects a remote area large enough to represent a credible fire.

Question 21Water Supply Analysis and Hydraulic Calculations

During a water supply flow test for a sprinkler system, the gauge reading taken before any test water is discharged is called which pressure?

  1. Static pressure Correct answer.
  2. Residual pressure
  3. Flow pressure at the test hydrant
  4. Normal operating pressure of the system

Explanation

Static pressure is the gauge reading with no water moving through the test assembly. Residual pressure, by contrast, is read while the test flow is being discharged, so it reflects the supply under demand. The static reading establishes the no-flow starting point for the supply curve.

Question 22Water Supply Analysis and Hydraulic Calculations

In the Hazen-Williams friction loss formula used for sprinkler piping, what does the C-factor describe?

  1. The discharge coefficient of the sprinkler
  2. The velocity pressure at the outlet
  3. The elevation change along the pipe
  4. The internal roughness of the pipe Correct answer.

Explanation

The C-factor is the Hazen-Williams roughness coefficient for the inside of the pipe. A lower C value represents a rougher pipe and produces greater friction loss for the same flow and diameter. It is not the sprinkler K-factor or a pressure coefficient.

Question 23Water Supply Analysis and Hydraulic Calculations

A sprinkler has a K-factor of 5.6. What is its approximate discharge when the pressure at the sprinkler is 7 psi?

  1. 5.6 gpm
  2. 39.2 gpm
  3. 7.0 gpm
  4. 14.8 gpm Correct answer.

Explanation

Discharge from a sprinkler follows Q = K times the square root of pressure. For K = 5.6 and P = 7 psi, Q = 5.6 × √7 ≈ 5.6 × 2.646 ≈ 14.8 gpm. Multiplying K by pressure directly would give the incorrect 39.2 gpm.

Question 24Water Supply Analysis and Hydraulic Calculations

A sprinkler demand is 650 gpm at the base of the riser. The design includes a 250 gpm hose allowance. How is the hose allowance applied in the hydraulic calculation?

  1. It is divided equally among all sprinklers in the remote area.
  2. It is added to the sprinkler demand at the system connection to the supply. Correct answer.
  3. It is subtracted from the sprinkler demand before comparing to supply.
  4. It is added to the flow at the most remote sprinkler.

Explanation

Hose allowance is a flow allowance for manual firefighting and is not discharged from the sprinklers in the remote area. It is added to the sprinkler demand at the system connection, such as the base of the riser, before the supply is compared with the total demand. Spreading it among sprinklers would distort the hydraulic calculation.

Question 25Water Supply Analysis and Hydraulic Calculations

A flow test shows 80 psi static and 60 psi residual at 1,000 gpm. Using the standard N^1.85 supply curve, what is the approximate available pressure at 800 gpm?

  1. 66.8 psi Correct answer.
  2. 64.0 psi
  3. 60.0 psi
  4. 70.0 psi

Explanation

The supply curve uses the pressure drop from static to residual at the test flow, scaled by the 1.85 power of the flow ratio. Here the drop is 20 psi at 1,000 gpm; at 800 gpm the drop is 20 × (0.8)^1.85 ≈ 13.2 psi. Subtracting that from 80 psi leaves about 66.8 psi.

Question 26Water Supply Analysis and Hydraulic Calculations

A sprinkler is 30 ft above the point where the system demand is calculated. What pressure is needed at that lower point to provide 50 psi at the sprinkler, ignoring friction?

  1. 37.0 psi
  2. 63.0 psi Correct answer.
  3. 13.0 psi
  4. 50.0 psi

Explanation

Elevation pressure is about 0.433 psi per foot of height for water. A 30 ft rise therefore costs 30 × 0.433 ≈ 13.0 psi. Adding that loss to the required 50 psi at the sprinkler gives about 63.0 psi at the lower point.

Question 27Water Supply Analysis and Hydraulic Calculations

For a dry-pipe sprinkler system using the density/area method, how is the remote area normally adjusted compared with a wet-pipe system of the same hazard?

  1. It is unchanged.
  2. It is increased by 30 percent. Correct answer.
  3. It may be reduced by 30 percent.
  4. It is doubled.

Explanation

Dry-pipe and double-interlock preaction systems are given a larger remote area because the initial air must be expelled before water reaches the sprinklers. The standard adjustment is a 30 percent increase in the remote area. A wet-pipe system does not receive that increase.

Question 28Water Supply Analysis and Hydraulic Calculations

A backflow preventer has a friction loss of 8 psi at the design flow. How should this loss be treated in the sprinkler hydraulic calculation?

  1. It is ignored because it is on the supply side.
  2. It is included as a pressure loss in the supply piping to the system. Correct answer.
  3. It is subtracted from the static pressure only.
  4. It is added to the sprinkler operating pressure at each sprinkler.

Explanation

A backflow preventer is part of the supply path and its friction loss occurs at the design flow. The loss must be charged against the available supply pressure in the hydraulic calculation, just like pipe friction. Ignoring it would overstate the pressure available at the sprinklers.

Question 29Water Supply Analysis and Hydraulic Calculations

In a sprinkler pipe segment, if the flow rate is doubled while the pipe diameter and C-factor remain the same, the friction loss increases by approximately what factor?

  1. 2.0
  2. 3.6 Correct answer.
  3. 1.85
  4. 4.0

Explanation

Hazen-Williams friction loss varies approximately as Q^1.85 when diameter and C are fixed. Doubling Q gives 2^1.85 ≈ 3.6 times the friction loss. The common mistake is to assume a linear doubling or to use the 4.0 factor from a square law.

Question 30Water Supply Analysis and Hydraulic Calculations

A supply test gives 70 psi static and 50 psi residual at 1,200 gpm. Using the N^1.85 method, what is the approximate maximum flow available at 40 psi?

  1. 1,100 gpm
  2. 1,490 gpm Correct answer.
  3. 1,650 gpm
  4. 1,200 gpm

Explanation

The allowable pressure drop increases from 20 psi to 30 psi, a ratio of 1.5. Flow scales as the 1/1.85 power of the pressure-drop ratio: 1,200 × 1.5^(1/1.85) ≈ 1,490 gpm. Using a linear ratio would incorrectly give about 1,800 gpm.

Question 31Water Supply Analysis and Hydraulic Calculations

What minimum operating pressure is generally required at a standard spray sprinkler in a hydraulically calculated sprinkler system, unless the sprinkler is listed for a lower pressure?

  1. 20 psi
  2. 15 psi
  3. 7 psi Correct answer.
  4. 4 psi

Explanation

NFPA 13 establishes 7 psi as the minimum operating pressure for standard spray sprinklers unless a specific listing permits otherwise. Design calculations must use at least this pressure at the hydraulically most remote sprinkler.

Question 32Water Supply Analysis and Hydraulic Calculations

In a tree-type sprinkler system, where does the hydraulic calculation normally begin?

  1. At the base of the riser
  2. At the fire department connection
  3. At the hydraulically most remote sprinkler Correct answer.
  4. At the water supply main

Explanation

Hydraulic calculations start at the hydraulically most remote sprinkler, which usually has the lowest pressure, and proceed back through the piping to the supply. The required pressure and flow are accumulated at each junction and pipe segment.

Question 33Water Supply Analysis and Hydraulic Calculations

A design density of 0.20 gpm/ft² is required over a 1,500 ft² remote area. What is the minimum sprinkler flow for that area?

  1. 300 gpm Correct answer.
  2. 450 gpm
  3. 150 gpm
  4. 250 gpm

Explanation

Multiply design density by the protected area: 0.20 gpm/ft² × 1,500 ft² = 300 gpm. This is the sprinkler demand before hose allowance and other additions.

Question 34Water Supply Analysis and Hydraulic Calculations

For a 2,000 ft² remote area, what is the minimum required length of the rectangular design area using the 1.2√A rule?

  1. 53.7 ft Correct answer.
  2. 44.7 ft
  3. 48.0 ft
  4. 50.0 ft

Explanation

The length of the remote-area rectangle is 1.2 times the square root of the design area: 1.2 × √2,000 = 53.7 ft. The width is then the design area divided by that length.

Question 35Water Supply Analysis and Hydraulic Calculations

How are elbows, tees, and valves normally accounted for in a sprinkler hydraulic calculation?

  1. They are converted to an equivalent length of straight pipe. Correct answer.
  2. They are added as a fixed 10 psi loss per fitting.
  3. They are included only in gridded systems.
  4. They are ignored when the pipe is Schedule 40.

Explanation

Fittings and valves add friction loss, so they are converted to equivalent lengths of straight pipe and added to the actual pipe length. The total equivalent length is then used in the friction-loss calculation.

Question 36Water Supply Analysis and Hydraulic Calculations

Why is a safety margin often added when comparing available water supply with sprinkler system demand?

  1. To reduce the required design density
  2. To account for flow-test uncertainty and future supply degradation Correct answer.
  3. To increase the sprinkler K-factor
  4. To eliminate the need for a backflow preventer

Explanation

A flow test represents a snapshot and can overstate long-term supply because of main changes, aging, or future demands. A margin, often 10 to 20 psi, helps ensure the system remains adequate.

Question 37Water Supply Analysis and Hydraulic Calculations

For a centrifugal fire pump, what is the maximum allowable shutoff (churn) pressure as a percentage of rated pressure under NFPA 20?

  1. 130%
  2. 140% Correct answer.
  3. 120%
  4. 100%

Explanation

NFPA 20 limits the shutoff pressure of a centrifugal fire pump to 140% of its rated pressure. This protects piping and system components from excessive pressure at churn.

Question 38Water Supply Analysis and Hydraulic Calculations

If the Hazen-Williams C-factor for a pipe decreases while flow rate and diameter stay the same, what happens to friction loss?

  1. It becomes zero.
  2. It stays the same.
  3. It decreases.
  4. It increases. Correct answer.

Explanation

The C-factor describes pipe roughness; a lower C means a rougher interior and more resistance. In the Hazen-Williams formula, decreasing C increases the calculated friction loss for the same flow and diameter.

Question 39Water Supply Analysis and Hydraulic Calculations

Using the Hazen-Williams formula, what is the approximate friction loss in 100 ft of 4.026 in. ID pipe carrying 500 gpm with C = 120?

  1. 5.0 psi
  2. 14.4 psi
  3. 7.2 psi Correct answer.
  4. 3.6 psi

Explanation

Using P = 4.52 Q^1.85 / (C^1.85 d^4.87) per foot gives about 0.072 psi/ft. For 100 ft, the loss is approximately 7.2 psi.

Question 40Water Supply Analysis and Hydraulic Calculations

What is the approximate water velocity in a 6.065 in. ID pipe carrying 500 gpm?

  1. 2.8 ft/s
  2. 8.4 ft/s
  3. 4.2 ft/s
  4. 5.6 ft/s Correct answer.

Explanation

Convert 500 gpm to about 1.11 ft³/s and divide by the pipe area of about 0.201 ft². The resulting velocity is approximately 5.6 ft/s.

Question 41Water Supply Analysis and Hydraulic Calculations

A sprinkler branch line has a friction loss of 0.06 psi per foot at the design flow. What is the friction loss in a 120 ft straight section of the same pipe at the same flow?

  1. 7.2 psi Correct answer.
  2. 4.8 psi
  3. 10.8 psi
  4. 14.4 psi

Explanation

Friction loss in a straight pipe run equals the unit friction loss multiplied by the length. Here, 0.06 psi/ft times 120 ft gives 7.2 psi. Fittings and elevation changes would be accounted for separately.

Question 42Water Supply Analysis and Hydraulic Calculations

A hydraulic calculation shows 62 psi available from the water supply and 70 psi required at the base of the riser for the sprinkler demand. What does this result indicate?

  1. The system is 8 psi short and needs a pump or redesign. Correct answer.
  2. The supply is adequate because only static pressure needs to be considered.
  3. The sprinkler demand must be increased until it equals 62 psi.
  4. The difference is only elevation and can be ignored.

Explanation

Available and required pressures must be compared at the same flow and reference point. A demand of 70 psi against 62 psi available leaves an 8 psi deficit, so the system is not adequate as calculated and needs a pump, tank, or design change.

Question 43Water Supply Analysis and Hydraulic Calculations

A fire pump has a rated capacity of 750 gpm at 90 psi. At exactly its rated flow, what net pressure rise is normally used as the pump contribution in the hydraulic calculation?

  1. 117 psi
  2. 135 psi
  3. 45 psi
  4. 90 psi Correct answer.

Explanation

The rated point of a fire pump is the flow and net pressure rise at rated capacity. At exactly rated flow, the pump contribution used in the calculation is the rated pressure, before adding suction pressure or deducting suction losses.

Question 44Water Supply Analysis and Hydraulic Calculations

In a hydraulically calculated sprinkler system, what is meant by the hydraulically most demanding area?

  1. The area with the highest ceiling clearance above the sprinklers.
  2. The area closest to the riser because friction loss is greatest there.
  3. The area whose flow and pressure create the highest supply demand. Correct answer.
  4. The area with the largest number of sprinklers regardless of pressure.

Explanation

The most demanding area is established by hydraulic calculation, not by physical distance or sprinkler count alone. It is the area whose required sprinkler flow and pressure produce the highest demand at the water supply.

Question 45Water Supply Analysis and Hydraulic Calculations

A single pipe carries 400 gpm with 6.0 psi friction loss. An identical pipe is installed in parallel, and the total flow remains 400 gpm split equally. What is the approximate friction loss through the parallel pair?

  1. 6.0 psi
  2. 1.7 psi Correct answer.
  3. 12.0 psi
  4. 3.0 psi

Explanation

Each parallel pipe carries 200 gpm, half of the original flow. Since friction loss varies approximately with flow to the 1.85 power, the loss in each pipe is about (0.5)^1.85 times 6.0 psi, or 1.7 psi, and the same loss applies across both.

Question 46Water Supply Analysis and Hydraulic Calculations

At the same flow and C-factor, what happens to friction loss in a pipe if its internal diameter is reduced to one-half?

  1. It increases by about 9 times.
  2. It increases by about 29 times. Correct answer.
  3. It increases by about 4 times.
  4. It increases by about 58 times.

Explanation

In the Hazen-Williams formula, friction loss varies approximately as diameter to the negative 4.87 power. Halving the diameter multiplies the loss by about 2^4.87, which is approximately 29.

Question 47Water Supply Analysis and Hydraulic Calculations

For a centrifugal fire pump, what minimum pressure is required at 150 percent of rated flow under NFPA 20 performance requirements?

  1. 65 percent of rated pressure Correct answer.
  2. 50 percent of rated pressure
  3. 100 percent of rated pressure
  4. 140 percent of rated pressure

Explanation

NFPA 20 requires a centrifugal fire pump to produce not less than 65 percent of rated pressure at 150 percent of rated flow. The 140 percent figure applies to the maximum allowable churn pressure, not to the 150 percent flow point.

Question 48Water Supply Analysis and Hydraulic Calculations

Why does a gridded sprinkler system require an iterative hydraulic solution rather than a single pass from the most remote sprinkler?

  1. The Hazen-Williams formula cannot be used in gridded piping.
  2. Sprinkler K-factors change whenever pipes are looped.
  3. Grid pipes have no friction loss and only elevation matters.
  4. Flow splits and rejoins, so continuity and junction pressures must balance. Correct answer.

Explanation

In a grid, flow can travel in either direction and split among multiple paths. The solution must satisfy mass continuity at each junction and a single pressure at each connected node, which usually requires iteration.

Question 49Water Supply Analysis and Hydraulic Calculations

Two sprinkler branches meet at a junction. Calculations show Branch A requires 24 psi and Branch B requires 20 psi at that junction to deliver design flow. In the system calculation, what pressure is assigned to the junction, and what does this mean for Branch B?

  1. 22 psi; the average pressure is used to split the flow.
  2. 44 psi; the two branch pressures are added at the junction.
  3. 20 psi; Branch B governs and Branch A will be overpressurized.
  4. 24 psi; Branch A governs, and Branch B must be balanced. Correct answer.

Explanation

The junction pressure must satisfy the more demanding downstream path. If 24 psi is set at the junction, Branch B receives more pressure than its design requires and will flow above design unless it is balanced by an orifice or revised piping.

Question 50Water Supply Analysis and Hydraulic Calculations

A flow test gives 55 psi residual at 500 gpm and 35 psi residual at 1,000 gpm. Using the N^1.85 supply curve, what is the approximate static pressure?

  1. 78 psi
  2. 58 psi
  3. 70 psi
  4. 63 psi Correct answer.

Explanation

The 1,000 gpm flow factor is 2^1.85, or about 3.60, times the 500 gpm factor. The 20 psi residual difference between those points means the drop from static to 500 gpm is about 20 divided by 2.60, or 7.7 psi, so static pressure is about 55 plus 7.7, or 62.7 psi.