SCO Plumbing & Gas key terms

A numerical load value assigned to a plumbing fixture based on its typical flow rate and usage pattern. It lets a designer size supply pipes and drainage systems by adding up the total demand.

The measured depth of water held in a fixture trap after normal use. It stops sewer gas from entering a building and is typically required to be between 38 and 102 mm deep.

A U-shaped fitting installed below a fixture that retains a water seal while allowing wastewater to pass. It traps debris and blocks sewer gas from rising back through the drain opening.

A vertical pipe that extends from the drainage system to outdoor air. It equalizes pressure in the drain pipes so trap seals are not siphoned away during discharge.

A one-way valve installed on a vent pipe that admits air when drainage creates negative pressure and closes to prevent sewer gas escaping. It is used where a full vent stack is impractical.

The pipe that carries wastewater from a single fixture trap to the branch drain or soil stack. Its size and slope must match the fixture's discharge and the local code requirements.

The main vertical drain pipe that carries toilet and other sanitary waste downward to the building drain. It usually continues upward as a vent to serve the fixtures connected to it.

The lowest horizontal pipe inside a building that collects waste from all stacks and branches and carries it to the building sewer. It must be sized and sloped to flow freely.

The pipe outside the building foundation that connects the building drain to the public sewer or private treatment system. It is often called the lateral and must maintain proper slope.

An accessible opening fitted with a removable cap that allows a plumber to clear blockages in a drain line. Codes specify where and how often cleanouts must be installed.

The pipe that brings potable water from the public main or private source into the building, ending at the first valve or meter. Its diameter determines available flow and pressure.

A device that stops contaminated water from flowing backward into the potable supply. Common types include reduced-pressure zone assemblies, double check valves, and vacuum breakers.

Any actual or potential link between the potable water system and a source of contamination. It must be eliminated or protected against with an approved backflow prevention device.

The unobstructed vertical distance between a water supply outlet and the flood level rim of a fixture or receptacle. It is the most reliable form of backflow protection.

A loud banging or knocking in pipes caused by a sudden stop in water flow, such as when a valve closes quickly. Arrestors or properly sized pipes reduce the pressure surge.

A device installed on a water supply line that lowers incoming pressure to a safe, usable level. High pressure can damage fixtures and cause water hammer and leaks.

A valve that blends hot and cold water to deliver a controlled, safe outlet temperature. It is used at fixtures such as showers and bathtubs to prevent scalding.

Water that has been blended to a moderate, controlled temperature for safe use at fixtures. It is distinct from hot water stored for sanitation and from cold supply water.

The downward fall of a drain pipe expressed as a ratio or percentage per unit of length. Correct slope keeps solids moving and prevents standing water and blockages.

The total measured length of a pipe run including all fittings and changes of direction. It is used when calculating pressure loss and sizing gas and water piping.

A method of expressing the pressure loss of fittings and valves as an added length of straight pipe. It simplifies sizing calculations for gas and water distribution systems.

The reduction in pressure as fluid or gas flows through a pipe or fitting due to friction and elevation change. Sizing must keep pressure drop within acceptable limits for appliances.

A pump installed in a pit to remove accumulated groundwater or drainage from a building. It typically discharges to an approved location outside the foundation.

A one-way valve installed in a drain line that closes automatically to prevent sewage from backing up into a building during surcharge or flooding of the public sewer.

The network of pipes, fittings, valves, and regulators that delivers fuel gas from the meter or supply point to appliances. It must be sized, installed, and tested to code.

The utility device that measures the volume of gas delivered to a building. It also marks the boundary where the utility's responsibility typically ends and the customer's piping begins.

A device that reduces and maintains gas pressure at a set level for downstream piping and appliances. It protects equipment from overpressure and keeps combustion consistent.

The gas pressure measured at the appliance manifold, downstream of the appliance regulator. It is checked with a manometer during commissioning and service to confirm correct operation.

An instrument that measures low gas pressure, often a U-tube or digital gauge. It is used for pressure tests, manifold pressure checks, and leak detection on gas systems.

A procedure that pressurizes a gas piping system with air or inert gas and monitors the gauge to confirm there are no leaks. Duration and test pressure are set by code.

The process of finding gas escapes using approved methods such as soap solution, electronic detectors, or pressure monitoring. Open flames must never be used for this purpose.

A fitting arrangement installed on the gas line near an appliance that catches dirt and debris before it reaches the controls. It is also called a dirt pocket.

A flexible or semi-rigid listed connector that joins the gas piping to an appliance. It must be installed without sharp bends and protected from damage and movement.

A manually operated valve installed in the gas line ahead of an appliance so the gas supply can be isolated for service or emergencies. It must be accessible and clearly identified.

The air supplied to a gas appliance for burning fuel. Inadequate combustion air causes incomplete burning, carbon monoxide production, and poor appliance performance.

The passage or pipe that carries combustion products from an appliance to the outdoors. It must be correctly sized, sloped, and terminated to ensure safe venting.

A colorless, odorless, toxic gas produced by incomplete combustion. Gas systems must be vented and adjusted properly, and CO alarms are required in many occupancies.

British thermal unit, the amount of heat needed to raise one pound of water by one degree Fahrenheit. It is the standard unit for rating gas appliance input and heat output.

The ratio of a gas's density to that of air. Natural gas is lighter than air and rises, while propane is heavier and settles in low areas, affecting leak detection and ventilation.