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Plumbing Terms and their Definitions


A list of plumbing terms and definitions 

 Air Gap A device mounted at the back of certain plumbing fixtures allowing discharge water to move freely into a drain pipe, but preventing contaminated water from back siphoning.
Air Lock The blockage of liquid flow of liquid due to an air bubble in the line
Anti-Siphon A device helping to prevent back-flow, for example on sprinklers, sump pumps; Prevents water from reversing back into the feed supply.
Back Flow When water travels from one system back into any part of the main distribution system; Generally caused by siphoning.
Back Flow Preventer A device used to prevent backflow into a potable water supply. 
Back Pressure Pressure that resists the flow of fluid in a pipe system.
Back Siphoning Negative pressure that causes backflow conditions.
Backup Sump Pump A secondary sump pump, usually powered water pressure or battery power. Takes over pumping when the primary sump pump fails.
Bernoulli's Law The principle that a stream of liquid or gas gives off less sideways pressure while it is in motion than while it is at rest.  Consequently, fluids appear to be drawn into a stream, but in reality are pushed in by the higher outside pressure.
Braided Tubing Flexible pressure tubing encased in braided threads of steel. The braiding protects the tube from damage due. They are often used in water supply lines for fixtures like toilets, sinks, or water heaters
Bushing A pipe fitting that is used to join different sized pipes.
Cast Iron Metal made from casting on molds, covered with a porcelain enamel coating.  Used to make fixtures like sinks or tubs. 
Centrifugal Pump A pump that transports water via centrifugal force created by the rapid spin of an impeller, which forces the water through a discharge outlet.
Check Valve A device installed in a pipe system that allows water to flow in only one direction. Used to prevent backflow.
Cock A faucet or valve used to stop or regulate liquid flow.
Compression Fitting A type of tubing or pipe connection, in which a nut and sleeve are placed over a copper or plastic tube, compressing tightly around the tube as the nut is tightened, which creates a positive grip and seal without soldering or gluing. Also refers to a flexible connector with a nut and gasket that attaches to a SAE standard compression thread, without using a sleeve or ferrule.
Compression Valve A type of valve used for water faucets that activates by raising or lowering a horizontal disk by a threaded stem. Uses compression fittings.
Corrosive Water Low pH water that has the ability to corrode metal plumbing fixtures and pipes.
Cross-Connection Any connection that could allow wastewater to enter the potable water supply.
Discharge Tube Tube that connects sump pump to the drain line.
Dope Lubricant paste used for sealing pipe threads.  
Dynamic Pressure The water pressure while water is flowing.
Elbow A fitting that has 2 openings, allowing a pipe line to change direction.  Often referred to by their angle.
Elevation The vertical distance between the level at which fluid enters a pipe and the level at which it leaves the pipe.
Female Fitting
A fitting into which a pipe or another fitting gets inserted.
Female Threads Threads that are on the inside of a fitting.
Ferrule A metal reinforcement insert that prevents the compression of a pipe as it enters fittings.
Fitting A pipe system component that joins together two sections of pipe.  Examples include: elbows, couplings, bushings, bends, or tees.
Flexible Connector A braided hose connecting a faucet or toilet to the water supply stop valve.  It is usually reinforced hose made from stainless steel, PVC, or polyester. 
Float Ball A ball-shaped float that rises or falls with the water level in a tank or sump pit.  
Floor Drain Drainage fitting that is positioned flush with the floor.  It is used in basements and showers.
Flow Control Valve Device that reduces water flow to a plumbing fixture. Typically used to improve efficiency and lower water costs. 
Flow Rate The rate that liquid flows, typically in gallons per minute (GPM) or gallons per hour (GPH).
Flux Paste that is applied to copper pipes and fittings before soldering takes place, in order to help the fusion process, while preventing oxidation.
French Drain A covered ditch that contains a layer of stone or other type of permeable material.
Friction Loss The loss of water pressure resulting from the turbulence created in water while it travels through a pipe.
Frost Line The depth that frost penetrates to, in the ground.
GFCI Stands for Ground Fault Circuit Interrupter. A device that cuts off the flow of electricity when a short circuit is detected.
GPH Gallons Per Hour.
GPM Gallons Per Minute.
Grey Water Waste water from sinks, showers, and bathtubs, although not toilets.
Ground Water Water that naturally rises in the ground from the water table.
Hanger A device that helps to support a pipe.
Hard Water Typically water hardness is a measure of calcium or dissolved solids, measured in parts per million. Hard water usually ranges from 100 to 250 ppm.
Head Water or steam pressure in a closed system - the difference in gravitational force exerted by a liquid at two different heights.
Hydraulic Pressure Pressure in a system that contains non-compressible liquid.
Hydrostatic Pressure Pressure exerted by liquid at rest.  Typically pertains to water pressing inward against walls, foundations, or floors.
ID Inside diameter. Pipes are specified by their inside diameter.
Impeller A spinning wheel with vanes that is used inside a centrifugal pump. As it spins, it draws in fluid and moves it to the discharge outlet.
Integral Vacuum Breaker A device that keeps water from back-flowing into the fresh water supply.
Laundry Tub A deep sink found in a laundry room. 
MIPC Male Iron Pipe Connection. External threads on pipe or fittings.
Main The primary water supply or drain artery of a system. 
Male Fitting Fitting that gets inserted inside another fitting.
Non-Potable Water that is not suitable for drinking.
O-Ring Round rubber washer used to make a watertight seal.
OD Outside Diameter of a pipe.
Outlet/Discharge The opening that water exits a pump through.
PEX Cross-linked polyethylene tubing that has become increasingly used for water supply lines. 
PSI Pounds per Square Inch
PVC Polyvinyl Chloride. A rigid white or cream-colored plastic pipe that is used in non-pressure systems, for example, in drainage, waste, or vent systems.
Perforated Pipe A pipe that discharges water through small, closely spaced holes or nozzles for irrigation.
Pipe Dope Pipe-joint compound used to seal threaded fittings.
Pitch The slope of a drain pipe.
Plug Male threaded fitting used to seal the end run of a pipe.  
Plumb Exactly vertical. 
Potable Water Water suitable for drinking.
Pressure Head Pressure in a plumbing system.
Pressure Loss Measure of the loss of pressure that occurs whenever water moves through a pipe or when water moves uphill against the force of gravity.
Pressure Reducing Valve A valve that automatically reduces water pressure to a specified pressure.
Pressure Regulator A device used to maintain a uniform pressure.
Reducer Fitting connecting different sized pipes.  
Scale A coating or layer, often of calcium, that can prevent heat transfer.
Schedule Numbers that specify the thicknesses of pipe wall.
Sediment Substance that settles at the bottom of a water tank. 
Solder A metal alloy, melted to fuse a joint between metal pieces. 
Static Discharge Head Vertical distance from a pump to the highest outlet point in the water system.
Static Lift The vertical distance between the water level at the source and discharge of a pump system. 
Static Pressure The pressure when water is not flowing.
Suction Head The head measured at the suction side of a pump. This is then subtracted from the discharge head to get the head being produced by the pump. 
Sump A pit for draining or collecting water.
Sweating Refers to either soldering or condensation being formed on the outside of pipes or toilets.
Tee A fitting shaped like a “T.” Has 3 openings that allow another pipe to be connected at a 90 degree angle.
Teflon Tape A fluorocarbon polymer used to wrap pipe threads to create a seal.
Vacuum Breaker An device that prevents siphoning and backflow.  Keeps contaminated water from flowing backward into the water supply system.
Valve A device that regulates the flow of liquid.
Venturi A tube that is tapered in the middle, creating an increase in the flow velocity of a liquid and a corresponding decrease in its pressure. Used to creating suction in a vacuum pump.
Water Hammer A loud banging noise that is caused by the hydraulic shock from abruptly shutting off a water supply.
Water Hammer Arrestor A device that absorbs the hydraulic shock caused by a sudden water shutoff.
Wye A Y-shaped pipe fitting that can be used to create 3 branch lines.