- Carrier fitting
- A floor-anchored steel frame set inside the wall that carries the weight of a wall-hung water closet or lavatory. It also holds the waste connection and mounting bolts in the right position, which is why it, not a closet flange, is the answer for wall-mounted bowls.
- Fixture unit
- A design number that weights how much load a fixture places on drainage or supply piping, based on its flow rate and how often it is used. Code tables convert total fixture units into required drain, vent and water pipe sizes, so planning questions depend on this concept.
- Developed length
- The total run of a water pipe measured along its centerline, including an allowance for fittings, from the source to the farthest outlet. Combined with available pressure and fixture demand, it controls how large the supply pipe must be to deliver enough flow at the end of the line.
- Wet vent
- A vent pipe that also carries waste from another fixture, so one pipe does two jobs for a group such as a bathroom. The code limits which fixtures may share it and how the pipe is sized, which makes it a common venting layout question.
- Island fixture vent
- A venting method for a sink in a kitchen island, where no wall exists to carry a vent upward. The vent loops up under the counter to a height above the fixture's flood level, then drops below the floor to connect to the vent system.
- Trap arm
- The horizontal stretch of a fixture drain between the trap and the point where it meets the vent. Its allowed length depends on pipe size and slope, because a trap arm that runs too far can siphon the water seal and let sewer gas into the room.
- Combination wye and eighth bend
- A single fitting that joins a branch to a horizontal drain with a gentle sweep and turns flow toward the downstream pipe. It keeps solids moving and gives cleanout access in line, so it is chosen over a sanitary tee in many horizontal drain connections.
- Backwater valve
- A fitting installed in a building drain or sewer that closes automatically when sewage flows backward from the public main. It protects fixtures that sit lower than the next upstream manhole cover, and it must stay accessible so it can be cleaned and maintained.
- Water hammer arrester
- A sealed, air-cushioned device placed near quick-closing valves, such as those on washing machines, that absorbs the pressure shock created when flow stops suddenly. Without one, pipes can knock and joints can loosen over time.
- Thermal expansion tank
- A small pressurized vessel on the cold supply to a water heater that takes in the extra volume created as water heats in a closed system. It prevents pressure spikes that would otherwise trip the relief valve or strain the fixtures.
- Temperature and pressure relief valve
- The safety valve on a water heater that opens when either heat or pressure inside the tank exceeds its setting. Its discharge pipe must be unvalved, sized to the outlet and run to a safe, visible location, so the release cannot be blocked or scald anyone.
- Pressure-reducing regulator
- A valve at the building's water entry that lowers high street pressure to a safe working level for fixtures and appliances. Knowing why it is required, and how it interacts with thermal expansion, helps with both supply sizing and repair questions.
- Reduced-pressure principle assembly
- A high-protection backflow preventer with two check valves and a relief port between them that dumps water to atmosphere if both checks leak. It guards against both backsiphonage and backpressure where a contaminant could be hazardous to health.
- Atmospheric vacuum breaker
- A simple backflow device that opens to air when supply pressure drops, stopping backsiphonage. It cannot hold under continuous pressure and must sit above the highest outlet it protects, so its placement matters as much as its presence.
- Cross-connection
- Any physical link between drinking water piping and a possible source of contamination, such as a hose submerged in a bucket or a boiler feed. Recognizing these links and choosing the proper protective device is a recurring theme in water supply questions.
- Drip leg
- A short, capped vertical pipe at the low point of a gas line ahead of an appliance connection. It collects dirt, scale and condensate before they reach the appliance's gas valve, and it is a standard detail in fuel gas piping layout.
- Dielectric union
- A fitting with an insulating gasket and sleeve that joins pipes of different metals, such as copper to steel. By separating the metals electrically, it slows galvanic corrosion at the joint, a common cause of leaks at water heater connections.
- Angle stop
- The small shut-off valve under a lavatory or behind a toilet that turns the supply at a right angle toward the fixture. It lets a fixture be serviced or replaced without shutting off the building, which is why finish work includes installing one at each fixture.
- Recirculation loop
- A hot water return path, with a pump or thermal driving force, that keeps water moving so distant fixtures get hot water fast. It saves the water otherwise run down the drain while waiting, which ties it to conservation, and it needs insulation to be effective.
