What is a backflow preventer and what plumbing terms should I know?

See this glossary of plumbing terms, so you'll know how to speak the language when you call a professional plumber or take a trip to the hardware store.
ABS - This stands for Acrylonitrile Butadiene Styrene. It is a rigid black plastic pipe used for drain, waste, and vent lines.

Access Panel - A covered opening in a wall or ceiling, near a fixture that allows access for servicing the plumbing system.

Aerator - A device screwed into the end of a faucet spout that mixes air into flowing water, and controls flow to reduce splashing.

Ambient Temperature - The average temperature of the air surrounding an appliance.

Angle Stop - A shutoff valve between the water pipes and a faucet. These are usually used to shut off water to a fixture in case of an emergency repair rather than daily usage.

Backflow Preventer - A device to prevent backflow, especially into a potable water supply. This is usually required for sprinkler systems, handheld showers, kitchen sprayers, etc.

Backwater Valve - A sewer line valve that prevents sewage from flowing back into the house.

Ballcock - The fill valve that controls the flow of water from the water supply line into a gravity-operated toilet tank. It is controlled by a float mechanism that floats in the tank water.

Bleed - To drain a pipe, tube, or hose of excess air.

Boiler - A sealed tank where water is heated and turned to steam for power or hot water.

Branch - Any part of a drain system other than the main, riser, or stack.

Branch Vent - A vent connecting one or more individual vents with a vent stack.

By-Pass Valve - Usually used by sprinkler systems, to by-pass the water filtration system.

Catch Basin - A large underground container for the collection of storm water run-off. It prevents dirt and other debris from polluting streams and lakes.

Circuit Vent - A vertical vent that is run from the last two traps on a horizontal drain line to the main vent stack of a building drainage system.

Cistern - A rainwater storage tank.

Cleanout Plug - A plug in a trap or drain pipe that provides access for clearing an obstruction.

Compression Fitting - A pipe connection that seals without soldering.

Compression Valve - A type of valve that works by raising or lowering a stem. Water passes through the valve by turning the faucet handle, which causes the stem to drop or rise.

Continuous Waste - Pipes under a double or triple sink that connect and remove wastewater.

Coupling - A vent pipe hood, which protects it from the elements.

Desanco Fitting - A type of compression adapter that connects tubular brass fittings to PVC pipe.

Direct Drain - A drain that flows directly into the waste arm without an airdrop.

Direct Tap - A clamping device that allows a branch line to be drilled and tapped off a main line.

Diverter - A valve that has a single inlet and directs water to one of two outlets. Commonly used with hand-showers and kitchen faucet sprayers.

DWV - Stands for Drain, Waste and Vent - referring to the pipes in a plumbing system that remove waste water.

Elbow - An angled fitting that alters the direction of the water line.

Extension Tailpiece - A slip on tube that connects the continuous waste to the p-trap.

Fall or Flow - The proper slope or pitch of a pipe for proper drainage.

Female IPS - A pipe connection where the threads are on the inside of the fitting.

Fixture - Any device that provides a supply of water and/or its disposal. For example: sinks, tubs, toilets.

Flapper Valve - The part on the bottom of the toilet tank that opens to allow water to flow from the tank into the bowl.

Float Ball - The floating ball connected to the ballcock inside the tank that rises or falls with changing water levels.

Flow Rate - The rate by which water is discharged from an outlet.

Flow Restrictor - Commonly found in showerheads, a flow restrictor limits the amount of water that passes through it.

Footprint - The area of floor space taken up by a water heater or other appliance.

Flux - A paste applied to copper pipes and fittings before soldering.

Gate - A device that controls the flow in a conduit, pipe, or tunnel.

Gasket - Flat device, usually made of fiber or rubber, used to provide a watertight seal between metal joints.

GPM - Stands for Gallons Per Minute. Measures the flow rate of faucets and showerheads.

GPF - Stands for Gallons Per Flush. Measures the flow rate of toilets.

Gray Water - Waste water from sinks, showers, and bathtubs, but not toilets.

Hard Water - Natural water containing impurities in various proportions.

Horizontal Branch - Lateral drain pipes that run from plumbing fixtures to the waste stack.

Horizontal Run - The horizontal distance between the point where fluid enters a pipe and the point at which it leaves.

Hose Bib - An outdoor faucet, also used to supply washing machines.

I.D. - Stands for inside diameter, to which all pipes are sized.

Indirect Wastes - Waste pipe used to discharge gray water into a floor drain.

Inlet - An intake opening.

Johnnie Bolt - Bolts that fasten the toilet to the floor.

Leader - A pipe that carries rainwater to the ground or sewer.

Lock Nut ? A fitting that connects two pieces of pipe.

Main - The primary water supply or drain system in which all the branches connect.

Male IPS - A pipe connection where the threads are on the outside of the fitting.

Manifold - A fitting that connects a number of branches to the main and serves as the distribution point.

Nipple - A short length of pipe installed between couplings or other fittings.

O.D. - Stands for Outside Diameter.

O-Ring - A round rubber washer used to create a watertight seal, usually around valve stems.

Outlet Sewer - A section of pipe in a septic system which runs between the septic tank and the drainage field.

Packing - A fibrous material that is used on faucets to prevent leaks.

Pitch - The downward slope of a drain pipe.

Plumb - Precisely vertical.

Potable - Water that is safe to drink.

Pressure Tank - A device used to pump water from a well.

PVC - Stands for polyvinyl chloride. A rigid white or cream-colored plastic pipe used in non-pressure systems, such as drainage and waste.

Reducer - A fitting that connects pipes of different sizes together.

Revent - A pipe installed specifically to vent a fixture trap.

Reverse Osmosis - A water treatment method in which water is forced through a semi permeable membrane that filters out impurities.

Riser - An upright or vertical pipe that feeds water to a fixture such as a showerhead.

Run - A complete or secondary section of pipe that extends from the supply to the fixture - or from the drain to the stack.

Service Entrance - A pipe connecting the water company piping to the water meter.

Sleeve - A pipe that is passed through a wall for the purpose of inserting another pipe through it.

Shutoff Valve - The valve that allows water supply to be cut off to one fixture without affecting the water supply to the entire house or building.

Spud - A short section of pipe or a threaded fitting that completes a connection.

Stack - The vertical main in the drain, waste, and vent system, extending one or more stories.

Tailpiece - Section of pipe that runs between a fixture outlet and the trap.

Tee - A T-shaped fitting with three openings used to create branch lines.

Trap - A curved section of drain line that prevents sewer odors from escaping into the atmosphere. All fixtures that have drains must have a "P" trap installed. A toilet is the only plumbing fixture with an "S" trap.

Usable Storage - The percentage of hot water that can be drawn from a tank before the temperature drops to a point that it is no longer considered hot.

Valve - A device that regulates water flow.

Valve Seat - The non-moving part of a valve. Water flow is stopped when the moveable portion of the valve comes in contact with the valve seat.

Vent - A pipe that allows air into a drain system to balance the air pressure, preventing water in the traps from being siphoned off.

Waste Arm - A drain extension pipe, usually used to extend a sink drain into a wall.

Waste & Overflow - A bathtub drain assembly that has an outlet at the top to remove overflow water when filling the tub and an outlet at the bottom to remove waste water when the tub is drained.

Water Meter - A device to measure the amount of water used by a household.

WYE - A Y-shaped fitting with three openings used to create branch lines.

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