SCO Plumbing & Gas flashcards

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

Fixture unit (FU)

A unit that expresses the drainage load of a fixture relative to a fixed standard, allowing pipe sizes to be summed and read from a sizing table.

Minimum drain slope

The smallest fall permitted on a drain, typically 1 in 50 for small pipe and 1 in 100 for larger pipe, set to keep solids moving.

Trap seal depth

The vertical water seal in a fixture trap, usually between 50 mm and 100 mm, which blocks sewer gas from entering the building.

Vent size rule

A vent must be at least half the diameter of the drain it serves and never smaller than 32 mm, so air can follow the discharge.

Air gap

The highest form of backflow protection, an unobstructed vertical distance between a supply outlet and the flood level of the receiving vessel.

Reduced pressure zone

A testable backflow assembly with two check valves and a relief valve, used for high-hazard connections where backpressure and backsiphonage are both possible.

Residual pressure

The pressure remaining at the most remote fixture while the system is flowing, which must meet the minimum for the fixture type.

Water supply pressure test

A test of the supply pipework at 1.5 times working pressure or at least 1000 kPa, held for two hours with no loss.

Drainage air test

A test of the drainage system using air at about 35 to 50 kPa, held for the period set by the code, used where a water test is impractical.

Developed length

The total equivalent pipe length of a run, including the actual pipe plus the equivalent lengths of fittings and valves.

Wet vent

A single pipe that serves as both the drain for one fixture and the vent for another, permitted only under the conditions set by the code.

Cleanout requirement

A cleanout is required at the base of each stack, at changes of direction over 45 degrees, and at intervals on long horizontal runs.

Backwater valve

A valve on the building drain that closes automatically to prevent sewage from the street sewer from flowing back into the building.

Grease interceptor

A device that slows kitchen waste flow so grease floats and is retained, sized by fixture units and retention time and pumped out periodically.

Thermal expansion of pipe

The increase in pipe length caused by temperature rise, calculated from the coefficient of expansion, the length, and the temperature change.

Water hammer arrestor

A device with a trapped air or gas cushion installed near a quick-closing valve to absorb the pressure surge when flow stops.

Natural gas heat content

The energy released by burning a unit volume of natural gas, approximately 37 to 38 MJ per cubic metre at standard conditions.

Propane heat content

The energy released by burning a unit volume of propane vapour, approximately 93 MJ per cubic metre, about two and a half times that of natural gas.

Specific gravity of gas

The ratio of a gas density to air density; natural gas is about 0.60 and propane vapour about 1.53, which affects where leaks collect.

Longest-run gas sizing

A sizing method that measures the developed length from the meter to the most remote appliance, sums the load, and reads the capacity table.

Gas pressure drop allowance

The permitted loss of pressure between the meter and the appliance, typically 0.125 kPa for low-pressure systems, used to select pipe size.

Appliance regulator

A device that reduces the supply pressure to the appliance manifold pressure and must be vented to a safe location.

Combustion air requirement

The air needed for complete burning plus dilution, roughly 1 cubic metre per megajoule of input, supplied through permanent openings.

Flue termination height

The minimum height above the roof and the clearance from windows and air intakes that a flue must meet to carry products away safely.

Gas leak test pressure

The pressure used to prove gas pipework tight, typically 1.5 times maximum operating pressure but not less than 7 kPa for low-pressure systems.

Gas detector placement

Methane detectors are mounted high because the gas is lighter than air, while propane detectors are mounted low because the vapour is heavier.

Flame failure device

A safety control that shuts off the gas supply if the flame is lost, using a thermocouple or flame rectification sensor.

Carbon monoxide risk

A poisonous gas produced by incomplete combustion, controlled by correct appliance adjustment, adequate air, and a working flue.

Gas pipe bonding

The connection of the gas piping to the electrical earth with a conductor sized by the electrical code, to prevent a difference in potential.

Drip leg

A capped vertical section at the appliance connection that collects condensate and debris before it reaches the controls.

Appliance connector limits

An approved flexible connector must not pass through a wall, floor, or ceiling, must not be concealed, and is limited in length.

Garage ignition height

In a residential garage, a gas appliance ignition source must be at least 450 mm above the floor because petrol vapour is heavier than air.