Red Seal Gasfitter Class A flashcards

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

Lower explosive limit (LEL)

The minimum gas concentration in air that will support combustion. For natural gas (methane) it is roughly 4 to 5 percent by volume; combustible gas meters display readings as a percentage of this limit.

CO air-free reading

A combustion analyzer calculation that removes the dilution effect of excess air, giving the true undiluted carbon monoxide concentration. It is the value compared against limits when judging combustion quality.

Lockout/tagout verification

After isolating gas and electrical energy, the worker tests at the appliance to confirm zero energy before starting work. Only the person who applied the lock may remove it.

Authority having jurisdiction (AHJ)

The body that enforces the adopted gas code in a region, such as a provincial gas safety authority or municipal inspector. Its adopted code and amendments govern the installation, not the model code alone.

Certified rating plate

The manufacturer's plate listing input, manifold pressure, gas type, clearances, and certification mark. It is the primary installation reference, and its requirements override generic code values where more stringent.

Gas permit and inspection

Required before installing or altering gas piping or appliances. The AHJ inspects the work before gas is turned on, so permits, pressure-test records, and start-up sheets form the compliance file.

Sediment trap (drip leg)

A capped fitting at the appliance connection that turns gas flow ninety degrees so dirt and scale fall out before reaching the controls. It must be accessible and installed per code.

CSST bonding requirement

Corrugated stainless steel tubing must be bonded to the building's electrical grounding system and protected from physical damage, per its listing and the manufacturer's instructions, because of its thin wall.

Pipe dope application

Listed gas pipe dope is applied to male threads only, leaving the first two threads bare so dope cannot enter the gas stream. Tape, where permitted, is wrapped in the direction of thread engagement.

Sling tension formula

For a two-leg bridle, each leg's tension equals the load divided by twice the cosine of the angle from vertical. Shallower angles raise tension sharply, so capacity must be derated.

Working load limit (WLL)

The maximum load a rigging component is rated to support in a specific configuration. Never exceed it, and never side-load a hook or use unmarked, non-rated hardware.

45-degree offset travel

For a forty-five degree offset, travel equals the offset multiplied by 1.414, and the run equals the offset multiplied by 1.0. These values set cut lengths and mark locations.

Nitrogen purge while brazing

Flowing nitrogen through copper tubing during brazing displaces oxygen and prevents internal oxidation scale, which would otherwise flake off and contaminate valves and orifices.

Pneumatic pressure test

A test of the completed gas piping at a pressure above operating pressure, for the duration set by the code and AHJ, with the test pressure never exceeding the appliance's rated limit.

Regulator lockup

The outlet pressure rise that occurs when flow stops and the regulator closes. Excessive lockup can overpressure downstream appliance controls, so it is checked along with flowing pressure.

Redundant combination gas valve

A valve assembly with two safety shutoff operators in series plus a manual valve and regulator. The series arrangement ensures a single operator failure cannot leave gas flowing to the burner.

Regulator vent piping

The regulator's diaphragm vent must be piped to a safe outdoor location or protected per code. It must never be plugged, because blocking it prevents the regulator from controlling outlet pressure.

Category I versus Category IV

Category I appliances are non-condensing and negative-pressure vented with a vertical vent; Category IV are condensing and positive-pressure vented, requiring listed plastic or stainless vent material.

Combustion air openings

A confined space needs two permanent openings, one high and one low, sized per code, or a listed louver. Louver blocking reduces free area, so the opening must be enlarged accordingly.

Clocking the gas meter

Timing a known volume of gas through the meter gives flow: cubic feet per hour equals cubic feet measured times 3600 divided by seconds. Compare to the rating plate input.

Natural gas to propane conversion

Requires the manufacturer's listed conversion kit, including orifice and regulator spring changes, plus a new rating label. An appliance fired on the wrong gas is a serious safety hazard.

T&P relief discharge termination

A water heater's temperature and pressure relief valve discharge pipe must terminate near the floor, typically within 150 to 300 millimetres, without reduction, trap, or threaded end.

Commercial gas train proving

Commercial burners use two safety shutoff valves in series with a valve-proving or leak-test circuit. The proving test must pass before each start, or the burner locks out.

O2 trim on industrial burners

Analyzer feedback corrects the air-fuel ratio as gas heating value and air density change, holding excess oxygen at target. It maintains efficiency and lowers carbon monoxide emissions.

Flame rectification

A flame conducts a small direct current between the flame rod and burner ground. The control must sense a minimum microamp signal to prove flame and keep the gas valve open.

Thermocouple versus thermopile

A thermocouple holds a standing pilot open; a thermopile generates enough millivolts to also power the main valve. A weak signal from either drops the valve out.

Air pressure proving switch

A switch that closes only when the combustion blower produces sufficient airflow, allowing ignition. A stuck-closed switch is a hazard and must be replaced, not adjusted.

Rollout switch

A manually reset safety device that trips when flame rolls out of the burner area, indicating blocked flue or poor combustion. It is reset only after the cause is corrected.

Start-up combustion baseline

Recording oxygen, carbon dioxide, carbon monoxide, and stack temperature at commissioning gives a reference. Later service compares readings; rising CO or falling CO2 signals a developing fault.

Flame lights then drops out

A burner that proves flame briefly and shuts down usually has a flame-sense fault: dirty or mispositioned flame rod, poor ground, cracked insulator, or weak thermopile signal.

Leak test after service

Any joint opened during service must be leak-tested with listed leak-detection fluid or an electronic detector, then the line purged and the appliance checked for combustion before leaving.

Draft hood function

A draft hood stabilizes draft and prevents downdraft from affecting combustion, while allowing flue gas to spill if the vent blocks. Spillage testing confirms it works during commissioning.