Pipe Sizing Exercises and Materials Questions
Diameter selection from flow and velocity, material properties, approved uses and support spacing.
16 questions · 3 calculation exercises
This section asks two different kinds of question that happen to share a name. Sizing questions are computational: given a flow and a velocity limit, find the bore, or given a bore and a flow, find the velocity. Materials questions are recall: which pipe is approved for which service, what joins to what, how far apart the hangers go. Both reward knowing that nominal size is a label rather than a measurement.
The sizing arithmetic reduces to the continuity equation, Q = A × V. Rearranged for diameter it gives d = √(4Q / πV), and in plumbing units the shortcut worth memorising is that velocity in feet per second equals 0.408 × Q (gpm) ÷ d² (inches), using the actual internal diameter. Exams set velocity limits rather than asking you to choose them: commonly cited practice keeps cold water at or below about 8 ft/s and hot water lower, nearer 5 ft/s, because erosion-corrosion accelerates with temperature. Those limits are industry guidance on service life, not code mandates, and a well-written question will say which it wants.
Nominal versus actual is where sizing questions are won. One inch Schedule 40 steel has an internal bore of 1.049 inches; nominal half inch Type L copper is about 0.545 inches inside; PEX of the same nominal size has a noticeably smaller bore than copper because the wall is thicker. Running the velocity formula on the nominal number instead of the real bore produces an answer that looks reasonable and is wrong, which is exactly the distractor the question offers you.
Materials questions concentrate on service limits and incompatibilities. CPVC takes hot water where PVC does not. ABS and PVC are both DWV materials but transition between them needs a mechanical joint rather than solvent cement in most jurisdictions. Copper and galvanized steel in contact set up a galvanic cell and need a dielectric separation. Support spacing differs by material and is stiffness-driven: plastic needs more support than copper, and vertical and horizontal spacings are different numbers.
What this topic tests
- Continuity equation applied in plumbing units, including the 0.408 Q/d² velocity shortcut
- Actual internal diameters versus nominal size, by material and schedule or type
- Velocity guidance for hot and cold water, and why the hot limit is lower
- Approved materials by service: potable, DWV, underground, above ceiling
- Hanger and support spacing by material, horizontal and vertical
Mistakes that cost marks
- Computing velocity from nominal diameter rather than actual internal diameter
- Using PVC on a hot water line where CPVC is the correct material
- Solvent-welding an ABS to PVC transition instead of using an approved mechanical coupling
- Applying copper support spacing to plastic pipe, which sags at those intervals
Pipe Sizing & Materials practice questions
Answer, check, and read why. Your result is saved in this browser, and anything you get wrong is queued for retry.
What does the schedule number of a steel or plastic pipe describe?
Calculators for this topic
Check your hand calculations against the same arithmetic, with the working shown.
Pipe Sizing & Materials. Frequently asked questions
What formula sizes a pipe from flow rate and velocity?
The continuity equation, Q = A × V, rearranged to d = √(4Q / πV). In plumbing units the convenient form is V = 0.408 × Q ÷ d², with Q in gpm, d the actual internal diameter in inches and V in ft/s. Size to the result, then move up to the next commercially available size.
Why is the recommended velocity limit lower for hot water?
Because erosion-corrosion is temperature-dependent. Moving water strips the protective oxide film from the pipe wall, and the hotter the water the faster that happens, so the commonly cited guidance holds hot water near 5 ft/s where cold is allowed closer to 8 ft/s. These are service-life recommendations rather than code limits.
Does nominal pipe size equal the actual diameter?
No. Nominal size is a designation. One inch Schedule 40 steel measures 1.049 inches inside; nominal half inch Type L copper is roughly 0.545 inches. Hydraulic calculations must use the actual bore, and questions are frequently built around that difference.
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16 questionsPlumbing Safety
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14 questionsInternational Plumbing Code (IPC)
How the International Plumbing Code is organised, what its tables govern and where it departs from the UPC.
16 questionsUniform Plumbing Code (UPC)
How the Uniform Plumbing Code is organised, its sizing approach and where it is stricter than the IPC.
14 questionsPlumbing Mathematics
Offsets and travel, grade and fall, volume, unit conversion and the geometry behind pipe layout.
18 questionsBlueprint Reading
Symbols and abbreviations, scale, isometric risers and reading a plan set in order.
12 questionsInstallation & Troubleshooting
Diagnosing faults from symptoms: siphonage, noise, slow drainage, pressure loss and backflow.
14 questionsPractice exams
Free Plumber Practice Test
Start here. Mixed practice, progress tracking and every exam in one place.
Journeyman Plumber Practice Test
Full-length paper weighted toward installation and code application.
Master Plumber Practice Test
Longer paper with more design, plan review and diagnosis.
Plumbing Exam Questions by Topic
All fourteen topics, with practice sets and explanations for each.
Plumbing Calculations Practice
Numerical exercises with tolerance checking and worked solutions.
Plumbing Code Practice Test
IPC and UPC structure, adoption and where the two codes diverge.
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