NITC Master Plumber flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Fixture unit (FU)

A dimensionless measure that converts dissimilar fixtures into a common load value for sizing drainage and water supply; one fixture unit equals roughly 1 gpm of demand.

Developed length

The total measured length of pipe along its centerline including all horizontal and vertical runs; fitting equivalents are added as a percentage during preliminary sizing.

Hunter's curve

A probability-based relationship between total fixture units and probable peak water demand; it accounts for non-coincident fixture use so peak flow is far below the arithmetic sum.

Static pressure gain

The pressure increase from elevation drop, equal to 0.433 psi per foot of fall (1 psi per 2.31 ft); used to check pressure at lower floors in tall buildings.

Thermal expansion tank

A device installed on closed domestic water systems downstream of a backflow preventer to absorb the volume increase as heated water expands, preventing relief valve discharge and pipe stress.

Copper tube type selection

Type K is used underground and for service lines, Type L for typical domestic distribution, and Type M only where code permits above-ground use; wall thickness decreases from K to M.

Trap arm length limit

The maximum developed length from the trap weir to the vent fitting, which varies with pipe size (for example 6 ft for 1-1/2 in pipe); exceeding it causes self-siphonage.

Backwater valve

A one-way device installed on drainage serving fixtures below the upstream manhole cover elevation to prevent sewage from reversing into the building during a surcharge.

Air admittance valve

A one-way vent that admits air into the drainage system when negative pressure develops and seals closed otherwise; it must be listed to ASSE 1050 or 1051 and located per code.

Vent stack sizing

Vent diameter is chosen from the total fixture units served; for example a 2 in vent serves up to 24 fixture units and a 3 in vent up to 84 under typical code tables.

Roof drain flow formula

Storm flow in gallons per minute equals roof area in square feet times rainfall intensity in inches per hour times 0.0104; intensity is taken from local 100-year, one-hour data.

Secondary roof drainage

A backup system of scuppers or additional drains that carries the design storm if primary roof drains become blocked; required by most codes for commercial roofs.

Grease interceptor sizing

Capacity is set by fixture units or flow rate and retention time, typically two hours for restaurant waste; it separates fats, oils, and grease before discharge to the sanitary sewer.

Air gap

The unobstructed vertical distance between a potable water outlet and the flood-level rim of a receptor; minimum is 1 in or twice the effective opening, whichever is greater.

Flood-level rim

The edge of a fixture at which water overflows onto the floor; it is the reference point for measuring air gaps and backflow protection critical levels.

Water closet spacing

Minimum 15 in from the centerline of a water closet to a side wall or partition and 30 in clear width in front; these dimensions come from accessible fixture clearance requirements.

Trap seal depth

The vertical distance between the trap weir and the dip of the trap, normally 2 to 4 in; too shallow risks evaporation and sewer gas, too deep risks slow drainage.

First-hour rating

The volume of hot water a storage water heater can deliver in one hour starting from a fully heated tank; it combines tank capacity with recovery rate and must meet peak-hour demand.

Recovery rate formula

Gallons per hour recovered equals input BTU/hr times efficiency divided by 8.33 times the temperature rise; it expresses how fast a heater reheats water.

T&P relief valve

A temperature and pressure relief valve set typically at 210 F and 150 psi that discharges full-size by gravity to a safe receptor with an air gap and no traps or reducers.

Combustion air requirement

Confined spaces need 50 cubic feet of air per 1,000 BTU/hr of input, supplied through two openings, one near the top and one near the bottom of the enclosure.

Rough-in inspection

The inspection performed after piping is installed but before it is concealed by walls, ceilings, or slabs; the system must pass a pressure or water test first.

Authority having jurisdiction

The official or agency that enforces the plumbing code, issues permits, conducts inspections, and approves variances or alternate materials in a given jurisdiction.

Model code adoption

A model code such as the IPC or UPC becomes enforceable law only when a jurisdiction formally adopts it, often with local amendments that change specific requirements.

Reduced pressure zone assembly

A testable backflow preventer with two check valves and a relief valve that protects against both backpressure and backsiphonage; used for health-hazard connections.

Pressure vacuum breaker

A testable assembly that protects against backsiphonage only; it must be installed at least 12 in above the highest downstream outlet and cannot be used where backpressure exists.

Double check valve assembly

A testable backflow preventer with two check valves that protects against backpressure and backsiphonage for non-health hazards only; not approved for toxic or health-hazard connections.

DWV water test

A test in which the drainage system is filled with water to a 10 ft head above the highest point and held at least 15 minutes before inspection to reveal leaks.

Smoke test

A test that introduces smoke into the drainage system to locate leaks and improper connections; escaping smoke reveals open joints or missing vent connections.

Trap seal loss causes

Evaporation, capillary action, wind effect, momentum, and backpressure each can break a trap seal; diagnosis identifies which cause applies before selecting a remedy.

Trench protective system

A shoring, shielding, or sloping system required for excavations 5 ft deep or more; spoil piles must be kept at least 2 ft back from the trench edge.

Labor unit estimating

A method that multiplies installed quantity by a published labor unit in hours per unit, then applies a productivity factor for site conditions to estimate total labor hours.