Exam Cheat Sheet · Quick Reference

Oklahoma Plumbing Contractor and Natural Gas

Oklahoma  ·  PSI Services Contractor

Verified, not estimated. Every figure below is drawn from the official exam structure we maintain — question counts, passing standard and topic weighting. Practice questions are grounded in the source law with statute citations. We omit any figure we can't verify rather than guess at it.
Total questions
85
Passing score
75%
Exam time
180 min
Administered by
PSI Services Contractor
Format
Reference materials allowed

Oklahoma State Portion 85 questions

General Plumbing Knowledge and Regulations 10 Q · 12%
IPC Chapter 1 scope, intent, and applicability of the plumbing codePermit requirements, application procedures, and exempt workCode official duties, inspection authority, and enforcement powersRequired plumbing system tests and inspection typesPipe length calculations using fitting allowances for threaded, copper, and PVC fittingsOffset and diagonal calculations using angle constants (45°, 60°, other angles)Volume, pressure, and capacity calculations for water systemsPipe material types, weights, and schedules (standard, copper, plastic, cast iron)Head PressurePipe JointsSolvent Welded Pipe JointsCalculations of Area and Volume +12 more
Piping, Valves, and Control Valves 8 Q · 9%
Pipe joints, fittings, and connection methods for gas and water pipingWater supply and distribution pipe materials, standards, and fittingsValves: types, required locations, and control valve functions (pressure-reducing, backflow preventers, relief valves)Pipe length calculations: fitting allowances, center-to-center and end-to-end measurementsPiping support, hangers, and spacing requirementsPVC Piping and ConnectionsCPVC Piping and ConnectionsGalvanized Piping and ConnectionsCopper Tubing and ConnectionsCopper Piping and ConnectionsPolyethylene Piping and ConnectionsPEX Piping and Connections +5 more
Fixtures and Equipment 8 Q · 9%
Minimum number and type of plumbing fixtures by occupancy classificationFixture installation requirements (spacing, clearances, and setting)Individual fixture standards and waste outlet requirements (water closets, lavatories, showers, bathtubs, sinks, urinals)Flushing devices, shower valves, and temperature-limiting controls for fixturesWater heater installation, safety devices, and relief valve requirementsTrap requirements, prohibited trap types, and trap seal protectionInterceptors and separators (grease, oil, sand) installation and sizingGas appliance installation requirements (cooking appliances, water heaters, room heaters, clothes dryers)Identify Minimum Plumbing Needs for Structures/FacilitiesInstall Fixtures and Associated Equipment
Water Supply 10 Q · 12%
Backflow prevention devices, assemblies, and application requirementsWater distribution system design criteria including flow rates, pressures, and pipe sizingApproved piping materials, fittings, and joining methods for water service and distributionPotable water protection including cross-connection control and identification of nonpotable systemsValve requirements including full-open valves, shutoff valves, and pressure-reducing valvesWater pressure booster systems, water hammer arrestors, and thermal expansion controlHot water supply system requirements including temperature limits and recirculation systemsNonpotable water systems including graywater reuse and rainwater collection storage and distributionWater Supply and Distribution LinesProtection of Potable Water SupplyBackflow
Drains and Sewers 10 Q · 12%
Sanitary drainage pipe materials and standards (above-ground, underground, and building sewer)Drainage system sizing using fixture unit values and pipe sizing tablesSlope, installation, and fittings for horizontal drainage pipingCleanout requirements (location, spacing, size, and access)Sumps, ejectors, and below-grade drainage systemsBackwater valves and sewage backflow protectionStorm drainage system design and sizing (roof drains, conductors, leaders, and gutters)Indirect waste piping, air gaps, air breaks, and waste receptorsDrain and Sewer PipeBuilding SewersSewer and Drain CleanoutsSewage Ejectors and Sump Pumps +3 more
Vents 13 Q · 15%
Vent pipe sizing and developed length (IPC stack vents, vent stacks, individual/branch/circuit vents)Vent terminal location and termination requirements (roof extension height, clearances from openings, wall terminations)Venting methods and types (individual, common, wet, circuit, combination waste-and-vent, single-stack, island fixture)Air admittance valves (installation, location, size, prohibited installations, required outdoor vent)Vent connections and grades (dry vent rise, connection above drain centerline, grade back to drainage)Vent InstallationDeveloped Length
Traps, Interceptors, Indirect, and Special Waste 5 Q · 6%
Fixture trap requirements, dimensions, and prohibited trap typesTrap seal depth, protection methods, and primer devicesGrease interceptors and automatic grease removal devicesOil separators and sand interceptors for commercial applicationsIndirect waste piping requirements and air gap vs. air break distinctionsWaste receptors, standpipes, and hub drain installationSpecial waste neutralization for corrosive waste dischargeInterceptor and separator venting, access, and maintenance requirementsTrapsInterceptors and SeparatorsIndirect and Special Waste
Isometric Analysis 7 Q · 8%
Calculating center-to-center (c-c) pipe lengths from isometric diagramsCalculating end-to-end (e-e) pipe lengths using fitting allowances45° offset constants (1.414 diagonal multiplier, 0.707 offset multiplier) applied to isometric layoutsThree-pipe offset diagrams with rise, run, and diagonal relationshipsFitting allowances for threaded, copper, PVC, and cast iron fittings in isometric assembliesSolving multi-fitting assemblies with wyes, tee-wyes, and elbows from isometric drawingsRolling offsets and true offset calculation using the Pythagorean theoremReading and interpreting offset terminology (offset, diagonal, rise, run, travel) from pipe diagramsIsometric Drawings
Fuel Gas 10 Q · 12%
Gas pipe sizing methods, tables, and equations (longest length, branch length, hybrid pressure)Approved piping materials and fittings (steel, copper, CSST, polyethylene, prohibited materials)Pressure requirements, allowable pressure drop, and maximum operating pressureVenting systems for fuel gas appliances (vent types, sizing, termination, connectors)Combustion air requirements for gas appliances (indoor, outdoor, mechanical methods)Appliance installation requirements (location, clearances, access, prohibited locations)Pipe testing, purging, identification, and leak checkingPipe length calculations and fitting allowances for fuel gas pipingGas Distribution Pipe SizingGas Pressure RegulatorsHangers and SupportsDirection Changes +14 more
Safety 4 Q · 5%
Fall protection trigger heights and duty to provide fall protection (6-foot rule, specific work conditions)Personal fall arrest system components, specifications, and proper useGuardrail system requirements and specificationsLadder safety requirements, proper use, and inspectionPersonal protective equipment selection, provision, and maintenance (head, eye, face, foot, hearing protection)Safety net systems installation and inspection requirementsStairway construction requirements and stairrail/handrail specificationsFall protection training, certification, and retraining requirementsResponsibility for Providing Personal Protective EquipmentExcavation SafetyEmployee Protection in Trenches and ExcavationsSafety Training Requirements +13 more

Key Distinctions

Air gap (indirect waste)vsAir break (indirect waste)

An air gap is measured between the indirect waste pipe and the flood level rim of the waste receptor, while an air break is provided between the indirect waste pipe and the trap seal of the waste receptor.

IPC 2018 Chapter 8 Indirect Special Waste, Section 802.3.2
Equipment for food storage, preparation and handlingvsCommercial dishwashers, food utensil sinks, nonpotable clear-water waste

Food storage/preparation/handling equipment must discharge through an indirect waste by means of an air gap specifically, whereas dishwashers (802.1.6), utensil sinks (802.1.7) and nonpotable clear-water waste (802.1.5) may use either an air gap or an air break.

IPC 2018 Chapter 8 Indirect Special Waste, Section 802.1.1
Multiple-occupancy fixture countvsSingle-occupancy fixture count

For multiple occupancies the fractional numbers for each occupancy are first summed and then rounded up to the next whole number, while in single-occupancy calculations each fractional number is rounded up individually.

IPC 2018 Section 403.1.1
Threaded fitting allowancevsCopper / PVC fitting allowance

Threaded allowance is center-to-face (A) minus the thread-in (B) for each fitting, while copper and PVC allowances are center-to-face minus the depth of the solder cup/socket with no thread-in calculation.

Mathematics for Plumbers and Pipefitters (8th ed.), Page 44
No-Hub cast iron fitting allowancevsThreaded fitting allowance

For No-Hub cast iron the D dimension is subtracted directly from the center-to-center length with no thread-in deduction (pipe joins by stainless steel shield and clamp), unlike threaded pipe which threads into the fitting.

Mathematics for Plumbers and Pipefitters (8th ed.), Pages 107-108 (Unit 28, Cast Iron Assemblies with Various Bends, Sample Problem 1)
PVC solvent-cement jointsvsCPVC solvent-cement joints

PVC water supply joints require a purple primer conforming to ASTM F656 followed by cement not purple in color (ASTM D2564 or CSA B137.3), while CPVC uses an orange solvent cement conforming to ASTM F493.

IPC 2018 Section 605.21.3
PVC pipevsCPVC pipe

PVC strength decreases significantly as temperature rises (Sch. 40 rated 160 psi at 73.4°F), while CPVC is specified for water 120°F and higher with an upper working temperature of 215°F.

Mathematics for Plumbers and Pipefitters (8th ed.), Pages 46-47
Branch length method (gas sizing)vsLongest length method (gas sizing)

The branch length method sizes each unsized branch section using the length from the point of delivery to the most remote outlet in that branch plus the section load, while the longest length method uses the overall longest run for all sections.

IFGC 2018 (Oklahoma) Section 402.4.2
Shutoff valve locationsvsFull-open valve locations

Shutoff valves are required on supplies to sillcocks, appliances/mechanical equipment, and fixture supplies other than bathtubs and showers in one- and two-family dwellings, whereas water riser pipes in one- and two-family occupancies of two stories or less take a full-open valve rather than a shutoff valve.

UPC Sections 606.1 and 606.2
Wet ventvsCircuit vent / combination waste-and-vent

A wet vent carries the discharge of one fixture while venting others (classic single bathroom group), while circuit vents serve batteries of fixtures and combination waste-and-vent is a different, more restricted system.

Vent stackvsStack vent

The vent stack is a separate vertical vent pipe connecting near the base of the soil stack and rejoining above the highest fixture, while the stack vent is the extension of the drainage stack itself and is sized from Table 906.1 by stack size, DFU and developed length.

IPC 2021 Section 202
Lead action level (30 µg/m³)vsLead PEL (50 µg/m³)

The 30 µg/m³ 8-hour TWA action level triggers ancillary requirements such as exposure monitoring, medical surveillance and training, while 50 µg/m³ as an 8-hour TWA is the exposure limit that may not be exceeded.

29 CFR §1926.62(c)(1)
Underground inspectionvsFinal inspection

The underground inspection is made after trenches are excavated and bedded and piping installed but before any backfill, while the final inspection is made after the building is complete, all fixtures are in place and connected, and the structure is ready for occupancy.

IPC 2018 Section 107.2
General code requirementvsSpecific code requirement

Where a general and a specific requirement conflict the specific requirement governs, and where different sections specify different materials or methods the most restrictive governs.

IPC 2018 Section 102.1

Key Terms

Branch interval IPC 2021 Section 202 (Branch interval)
A vertical length of stack of 8 feet or more between the connections of horizontal branches; branches connecting less than 8 feet apart fall within the same branch interval.
Wet vent
A pipe that vents one or more fixtures while also carrying the discharge of another fixture, as in a single bathroom group.
Vent stack IPC 2021 Section 202
A separate vertical vent pipe installed to circulate air through the drainage system, connecting near the base of the soil stack and rejoining the stack vent above the highest fixture.
Air break IPC 2018 Chapter 8 Indirect Special Waste, Section 802.3.2
An indirect waste arrangement in which the separation is provided between the indirect waste pipe and the trap seal of the waste receptor.
Crown vent (prohibited) IPC 2021 Section 909.3
A vent connected within two pipe diameters of the trap weir, which is prohibited (e.g., less than 3 in for a 1½" trap, less than 4 in for a 2" trap).
Maximum trap-to-vent distance IPC 2021 Table 909.1
The limit on trap arm length from weir to vent by trap size (6 ft for a 1½" trap, 8 ft for a 2" trap); a water closet is a self-siphoning fixture whose distance is not limited.
Fitting allowance (threaded) Mathematics for Plumbers and Pipefitters (8th ed.), Page 39
The distance between the end of the pipe, which may be inside the fitting, and the center of the fitting, used to convert center-to-center into end-to-end length.
Set (offset terminology) Mathematics for Plumbers and Pipefitters (8th ed.), Review of Basic Fundamentals, Chapter 1, offset terminology section
A shortened form of "offset" meaning the perpendicular center-to-center distance between two parallel pipes; travel/diagonal is the connecting pipe and run is the horizontal leg.
¼ bend (cast iron) Mathematics for Plumbers and Pipefitters (8th ed.), Pipe Length Calculations, Chapter 2, cast iron fittings section
A cast iron fitting equal to 90° (¼ × 360°); a ⅛ bend is 45° and a ¹⁄₁₆ bend is 22½°, so the same offset constants as threaded fittings apply.
Type DWV copper tubing Mathematics for Plumbers and Pipefitters (8th ed.), Page 42
The copper tube type designed for drainage, waste and vent service; Types K and L serve underground and interior pressure service and Type M interior service.
Pipe schedules Mathematics for Plumbers and Pipefitters (8th ed.), Page 35
The three common pipe weights from lightest to heaviest: Schedule 40 (standard), Schedule 80 (extra-heavy) and Schedule 120 (double extra-heavy).
No-Hub connection Mathematics for Plumbers and Pipefitters (8th ed.), Page 105
One of the three recognized cast iron joining methods (with lead-and-oakum and compression gasket joints), made with a stainless steel shield and retaining clamp.
Permit exemption (repairs) IPC 2018 Section 106.2
Clearing stoppages or repairing leaks in pipes, valves or fixtures and removal/reinstallation of water closets need no permit, provided the work does not require replacement or rearrangement of valves, pipes or fixtures.
Permit expiration IPC 2018 Section 106.5.3
A permit expires by limitation and becomes null and void if the authorized work is not commenced within 180 days from the date of the permit.
Work without a permit penalty IPC 2018 Section 106.6.1
A person who commences work on a plumbing system before obtaining the necessary permit is subject to 100 percent of the usual permit fee in addition to the required permit fees.
Gas piping sizing requirement IFGC 2024 Section 402.1
Piping systems must be sized and installed to meet maximum demand and supply gas to each appliance inlet at not less than the minimum supply pressure required by the appliance.
Medical removal protection (lead) 29 CFR §1926.62(k)(1)(i)
Removal from lead work is required when periodic and follow-up blood tests show a level at or above 50 µg/dl, with up to 18 months of benefits (earnings, seniority, rights) per removal occasion.
Oral emergency action plan 29 CFR §1926.35(e)(3)
An employer with 10 or fewer employees may communicate the emergency action plan orally and need not maintain a written plan.

Formulas to Know

Cut (end-to-end) length of threaded pipee-e = c-c − total fitting allowance, where allowance = Σ(center-to-face A) − Σ(thread-in B); e.g., two ells: 2(1½") − 2(½") = 2"; or cut = c-c − (2 × takeoff) + (2 × thread engagement), e.g., 42 − 4½ + 1 = 38½"
Cut length for copper, PVC and No-Hub cast irone-e = c-c − sum of fitting allowances (copper/PVC allowance = center-to-face − depth of solder cup/socket; sweat allowance ½" per fitting end; No-Hub = subtract each D dimension directly, no thread-in). Examples: 10" − (⁹⁄₁₆ + ⁵⁄₁₆) = 9⅛"; 65¹⁄₁₆ − (3 + 3) = 59¹⁄₁₆"; 24 − (2 × ½) = 23.00"
45° offset (and reverse)travel (diagonal) = set × 1.414; run = set × 1.000 (run = set, and rise = set); set = diagonal × 0.707. Example: 20 × 1.414 = 28.28" ≈ 28¼"
Other offset-angle constants22½° offset: travel = set × 2.613 (10 × 2.613 = 26.13"). 60° offset: diagonal = offset × 1.1547 (cosecant 60°), run = offset × 0.5774 (cotangent 60°). Parallel 45° offsets: difference in length = 0.414 × spread
Rolling offset true offset, then traveltrue offset = √(set² + roll²); then travel = true offset × angle constant. Examples: √(12² + 10.5²) = 15.95"; √(12² + 9²) = 15.0", travel 45° = 15.0 × 1.414 = 21.2", travel 60° = 15.0 × 1.155 = 17.3"
Static water pressure and headpressure = height of water (ft) × 0.433–0.434 psi/ft (46 × 0.433 = 19.9 ≈ 20 psi); height = psi ÷ 0.433 (30 ÷ 0.433 = 69.3 ft), or psi × 2.304 ft/psi; static head depends on vertical elevation only
Drain fall, percent slope and invert elevationtotal fall = run (ft) × grade (in/ft) — e.g., 32 × ⅛ = 4 in; 48 × ¼ = 12 in = 1.00 ft; percent slope = (in per ft ÷ 12) × 100 (¼ in/ft = 2.08%); downstream invert = upstream invert − total fall (100.00 − 1.00 = 99.00')
Tank volume and gallon capacityCylinder: V = πr²h (r = ½ diameter) — 3.14 × 7² × 20 = 3,077.20 cu in; gallons = cubic feet × 7.48 (π × 2² × 6 = 75.4 cu ft × 7.48 ≈ 565 gal). Rectangular prism: V = L × W × H (30 × 36 × 4.5 = 4,860 cu ft); 1 cu ft = 1,728 cu in
Lead required for cast iron hub jointsAllow 12 oz of lead per inch of pipe size per joint; divide total ounces by 16 for pounds. Example: 2" pipe × 12 = 24 oz per joint × 6 joints = 144 oz ÷ 16 = 9 lb
Individual vent size and 40-ft upsizing ruleVent size = ½ the fixture drain size but never less than 1¼" (1½" drain → 1¼"; 2" drain → 1¼"; 3" drain → 1½"); if developed length exceeds 40 ft, increase one nominal size for the entire length (44 ft or 60 ft on a 1½" drain → 1½" vent)
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