Glossary of Terms


100% Coverage   The design goal of all sprinkler system designers. Sometimes used (incorrectly) in place of the term "head to head coverage". 100% coverage is the objective of head-to-head coverage. But head-to-head coverage does not always result in 100% coverage.

Acre Foot (also acre feet)   A measurement of water quantity most often used in agriculture. The amount of water needed to cover one acre of area with water one foot deep. Enough water to drown in, but not deep enough to swim in.

Acre Inch    See "acre foot" above and substitute "inch" for "foot".

Angle Valve   Refers to the water flow pattern into and out of the valve. Often used as control valves. Seldom used as isolation valves. The valve inlet is on the bottom of an angle valve and the outlet is on one side. Angle valves as a group tend to be very reliable and have lower friction losses than "globe" valves, the other common style used for control valves.

Anti-Siphon Valve   A control valve with a built-in atmospheric vacuum breaker (backflow preventer). Most commonly used in residential irrigation systems.

Atmospheric Vacuum Breaker (AVB)   A type of backflow preventer.

Automatic Valve   A valve which can be remotely operated. The remote operation method may be either electrical (the most common) or hydraulic. Automatic valves are commonly used as "control valves" for irrigation systems.

AWG-UF   The classification of the direct burial wire used for automatic sprinkler systems. Example: #14-1 AWG-UF means a 14 gauge wire, single wire cable, designed for direct burial (no conduit) in the ground. The wire should have this information stamped or printed directly on the wire's plastic insulation. The wire should be at least 18" deep for safety (in most areas this requirement is written into local law).


Backflow Preventer   A device that prevents contaminated water from being sucked back into the water source should a reverse flow situation occur.  In most places backflow preventers are required by law on all irrigation systems.

Ball Valve   This type of valve controls the water by means of a rotating ball with a hole through the center of it. When the hole is aligned with the water flow the water flows freely through the valve with almost no friction loss. When the ball is rotated so that the hole is not aligned the flow is completely shut off. Ball valves are used primarily as isolation valves. They tend to be very reliable and trouble-free. Ball valves as a group tend to require more effort to turn on and off than other valves. For larger size pipes butterfly valves are usually used rather than ball valves. If you're looking for a dirty joke, you'll need to keep looking.

Bushing  A bushing is a small piece used to connect two pipes of different sizes together. A standard reducer bushing has one male end (for the larger pipe) and one female connection (for the smaller pipe).

Butterfly Valves   This type of valve uses a rotating disk to control the water flow. A true butterfly valve has two half-disks, hinged together in the center. When the disks, or "wings" are folded together the water flows freely past them. when folded out into the water stream the wings block the flow. Most "butterfly valves" are really "rotating disk" valves. They have a single, round disk that rotates on an axle. When fully open the disk is rotated so that it is aligned with the water flow. To close, the disk is rotated at a right angle so that it fully blocks the flow. Butterfly valves are used as both isolation and control valves. Butterfly valves tend to be very reliable and trouble free. They are mostly used on larger pipe sizes, seldomly less than 3" in size. Ball valves are used on smaller size pipes.

Booster Pump   A device to increase the water pressure is a system where some pressure already exists. For example, if water comes from a water company at 40 PSI of pressure but you need 80 PSI of pressure for the irrigation system, you would use a booster pump to increase the pressure.


Cubic Feet   A measurement of water quantity, often used by water companies in the United States of America to measure water use by customers. A cubic foot is one foot in length, one foot in width, and one foot deep.

CL 125, 160, 200, 315   Pronounced "class-one-twenty-five", "class-one-sixty", "class-two-hundred" and "class-three-fifteen". Pipe classifications  (CL = class = classification) based on standard dimension ratios. Simply, CL 125 pipe is rated for 125 PSI working pressure, CL 200 for 200 PSI, etc. Most industry professionals will tell you that it's not wise to use pipe rated at less than twice the actual maximum water pressure level. In other words, for a water pressure of 100 PSI use at least CL 200 pipe.

Controller   A "timer" used to turn on and off an automatic irrigation system. Controllers range from very simple to extremely sophisticated computer systems that utilize modems, cell-phones, or radios and allow 2-way communication between the controller and the units (valves, meters, weather stations, soil moisture sensors, etc.) being controlled.

Coupling   A fitting used to join two sections of pipe together.

Cross   A fitting that joins 4 sections of pipe at one point forming a "cross". Reducing crosses are available which have different size outlets.

Cubic Meter  Measure of water quantity, often used by water companies to measure water use by customers. A cubic meter is one meter in length, one meter in width, and one meter deep.


Design Pressure   In the irrigation design the design pressure is the total pressure available to operate the irrigation system. Other uses of the term vary, but usually refer to the operating pressure at which a specific piece of irrigation equipment is designed to operate.

Draw Down   The depth (from the top of the well) to the water in a well when the pump is operating. The water level typically drops when the pump is running.

Drip Irrigation   Any type of irrigation system that applies water to the soil very slowly, thus the name "drip" irrigation. Currently the most efficient irrigation technology in terms of both water and energy use.

Drip System   An irrigation system that uses drip irrigation. See drip irrigation above.


Elevation Head   A measurement of pressure. Typical usage: "If you want to know more about elevation head you'll need to see the glossary definition for pressure head."

Elbow   A fitting used to change the direction of a pipe. For PVC and poly irrigation uses they are available in 90 degree and 45 degree bends. Some specialty elbows are available in other angles but have limited availability. You can remember elbows simply by their shape, they look like an "L".  PVC elbows are available with threads in both ends, threads in one end and a glued socket in the other, or with glue sockets in both ends. Insert elbows come with male threads and barbs, female threads and barbs, glue sockets and barbs, glue spigots and barbs, or barbs and barbs. 

Emitter   A term used with drip irrigation. The emitter, or dripper, is a small device that controls the flow going to the soil. Emitters come in many different flow rates and styles.


Female Adapter   A fitting used to adapt from solvent welded PVC to a threaded or barbed connection. Never, ever use a plastic female adapter on anything with metal threads.

Fittings   The generic name for the various parts that attach the pipes together. Includes bushings, couplings, crosses, ells, female adapters, male adapters, reducers, and tees. Fittings may be threaded, barbed, soldered, or welded to the pipe. (The glue or cement used on plastic fittings is a solvent which results in a welded joint.) Plastic fittings with threads should never be tightened with wrenches. Hand tighten them only.


Gallons per Minute  (GPM) A measurement of water flow primarily used only in the United States.

Gate Valve   Refers to the operating mechanism for the valve, which is a sliding gate which moves up or down to block the flow. Often used as isolation valves. Never used as control valves. Because the gate slides it is very subject to wear, and gate valves wear out fast when used often. Some gate valves use a wedge-shaped gate which holds up better. They are still not designed for regular use, but for emergency shut-off only.

Globe Valve   Refers to the water flow pattern into and out of the valve. Often used as control valves. Seldom used as isolation valves. The valve inlet is on one side of the globe valve and the outlet is on the other side. Globe valves as a group tend to be very reliable, but have slightly higher friction losses than "angle" valves, the other common style used for control valves.

GPM   Abbreviation used by irrigation designers writing "gallons per minute".

Gravity Flow   The term given a water system that relies on gravity to provide the pressure required to deliver the water. Consists of a water source located at a higher elevation than the water delivery points.      


Head Pressure See "pressure head".

Head   Short for "sprinkler head".

Head to Head   In irrigation "head to head" refers to the situation where sprinklers are spaced so that the water from one sprinkler throws all the way to the next sprinkler. Most sprinklers are designed to give the best performance when head to head spacing is used.

Hydraulics   The science of fluids in motion. As it relates to irrigation there are two sub categories for hydraulics. They are open-channel hydraulics (canals, ditches, streams, rivers, etc.) and closed channel (or closed conduit) hydraulics (pipelines, tanks, etc.).

Hydro-Zone   An area of an irrigation system where all the factors that influence the watering schedule are similar. Typical factors to be considered would be the type of plants, the precipitation rate of sprinklers or emitters, solar radiation, wind, soil type, and slope. See the related term "valve zone".


Isolation Valve   A valve used for isolating all or part of the irrigation system for repairs, maintenance, or winter shut-down (winterization). Common types of isolation valves are the ball valve, butterfly valve, gate valve, and white bread. 


K-Y Jelly   A clear, water soluble, non-toxic lubricant used for lubricating O-rings in water filters. Also sometimes used to lubricate threads and ease insertion of drip tube into fittings. Because it is water soluble it doesn't gum up emitters, filters, or sprinkler mechanisms.


Lateral   The name given to the pipes which go from the control valves to the sprinklers or drip emitter tubes.

Liters per Minute   A metric measurement of water flow used worldwide.


Mainline   The name given to the pipe(s) going from the water source to the irrigation control valves.

Male Adapter   The fitting used to adapt from solvent weld PVC to a male threaded end. When connecting to metal threads male adapters should be used, so that the plastic male threads screw into the metal female threads.


Nipple   The common plumbing term used in the irrigation trade for a short length of pipe, usually threaded on both ends.

Nozzle   The part of a sprinkler that the water comes out of. Usually a very carefully engineered part to assure a good spray pattern. In most cases the nozzle is removable so that it can be easily cleaned or replaced. With plastic nozzles replacement is generally preferred over cleaning as small scratches in the plastic can cause big problems with water distribution uniformity.


Operating Pressure   The pressure at which a device or irrigation system is designed to operate. Can mean just about anything depending on usage. There can be "optimum operating pressure" "minimum operating pressure", "maximum operating pressure" and "operating pressure range".


Polyethylene   A plastic used for manufacturing irrigation tubing. "Poly" for short. Poly pipe is almost always black in color, sometimes with a strip of a different color for identification. It is very flexible, and is usually sold in coils of 100 feet or more of tube. Poly pipe is often used in areas where the ground freezes 12" deep or more, and also in mountainous areas that are extremely rocky. Poly pipe uses insert type fittings where a barbed shank is shoved into the end of the tubing. These fittings must be clamped, the barbs alone will not hole the tube on the fitting. Exception- special barbed fittings made for sprinkler risers do not need to be clamped. Also see "PVC" for the most commonly used pipe material.

Poly Vinyl Chloride   The real name for PVC. (See PVC below.)

Pop-Up Sprinkler Head   A sprinkler head that retracts below ground level when it is not operating.

Precipitation Rate   A measurement of water application. The measurement is given in the depth of water applied to the soil. In other words the depth that the water would be if it didn't run-off or soak into the soil. In the USA precipitation rate is measured in inches per hour. In metric countries it is measured in millimeters per hour.

Pressure Gauge   A device used to measure water pressure. The best pressure gauges are "liquid filled", however most cheap gauges work good enough for irrigation use.

Pressure Head   Measurement of water pressure based on the water depth. Measurement is stated as "feet of head" or "meters of head". One foot of head is the pressure at the bottom of a 1 foot high column of water, which is also equal to 0.433 PSI. So it's really a measure of the weight of water of a given depth. It doesn't matter how much water is present, the pressure head is only determined by the depth of the water. The water pressure at the bottom of a 2" diameter, 20 foot tall water filled pipe is the same as the water pressure at the bottom of a 20 foot deep lake.

Pressure Vacuum Breaker (PVB)   A type of backflow preventer.

Pressure Loss   The term given for the loss of energy , in the form of pressure, that occurs whenever water moves through a pipe or any other piece of irrigation equipment. Pressure loss also occurs when water moves uphill against the force of gravity. If the total pressure loss in a piping system exceeds the available static water pressure the water will not flow. In landscape irrigation systems no flow means no grow.

PSI   Abbreviation used by irrigation designers for "pounds per square inch".

Pump   A device which increases the water pressure or moves water. Technically most pumps don't move the water, they increase the water pressure, and the water pressure moves the water.

PVC   Abbreviation for poly-vinyl-chloride. A type of plastic used to make water pipe. Usually white in color but sometimes is gray, brown, tan, or purple. If it's purple it means "reclaimed water", you don't want to drink the water in it!  


Reduced Pressure Backflow Preventer (RP)   A type of backflow preventer.

Reducer   A fitting used to change from one size pipe to another. Two types are generally available. The first, and most common is the reducer bushing (abbreviated "red. bush." or RB). The reducer bushing fits inside a coupling or other fitting on the large end. The pipe fits into the red. bush. on the small end. The other common reducer is a "bell reducer". The pipe fits inside the reducer on both ends of the bell reducer.

Riser   The connection between a sprinkler or other irrigation device and the pipe that supplies the water to it, usually consisting of a short nipple and sometimes a few elbows.


SCH 40 , SCH 80   Means "schedule 40, 80". Sometimes abbreviated "SCHED". A set of standards for pipe diameter and wall thickness used for both plastic and steel pipe. SCH 40 pipe is the standard type used for water pipes sized 1 1/2 and smaller. SCH 80 is a similar standard having thicker walls than SCH 40. Also see "CL 125, 160, 200, 315" for related standards.

Shrub Sprinkler Head   A sprinkler head mounted above ground level on a pipe, usually used for watering shrubs.

Slip   Slip is the term used to describe a solvent welded connection on a fitting. Normally refered as the "smooth" inside end of fitting vs. a threaded inside of fitting.

Socket   A socket is a female connection on a fitting. It can be threaded, or glued, but most of the time the term is used for glued fittings.

Spigot   A spigot is a male connection on a fitting. A spigot fits inside a socket. It can be threaded, or glued, but most of the time the term is used for glued fittings.

Spring   1. A place where the water flows from the ground. In most cases springs are the points at which the underground water table intercepts the earths surface, and thus, water flows from the ground. Some springs are the outlets of underground streams or rivers that flow through channels in the ground.

Sprinkler   Sprinkler heads are devices which distribute water over a given area for irrigation.

Square Spacing   The term given to a sprinkler head layout pattern where the sprinklers, when viewed from above, appear as more or less a square with one sprinkler in each corner. See also the more efficient "triangle spacing"

Static Water Pressure   The water pressure as measured when the water is not moving. The "not moving" part is critical, if the water is moving it isn't "static".. When measuring static water pressure all the water outlets on the pipe must be closed. So if you're measuring the static pressure at a house you connect the pressure gauge, then take the reading while all the faucets, the ice maker, etc., are turned off. Static water pressure is a measure of the water's energy potential.


Take-Off    The building industry term for an itemized list of materials used to build something such as a home, deck, or, even an irrigation system!

Tee    Fitting used to branch a side pipe off of a pipeline.

Total Pressure Head   The sum of all the factors which increase or decrease the available water pressure.

Triangle Spacing   The term given to a sprinkler head layout pattern where the sprinklers, when viewed from above, appear as a more or less equilateral triangle with one sprinkler in each corner. Triangular spacing results in the most uniform and efficient water application using sprinklers. Trickle Irrigation   Another name for drip irrigation. Probably a more accurate name since for most drip irrigation systems the water flow is more of a trickle than a drip.


VAC   Volts Alternating Current. Most electric control valves operate on 24 VAC. That's "alternating current", like household electricity, not "direct current" like batteries!

Valve   A device used to control the flow of water. Isolation valves are used to shut-off water for repairs. Control valves turn on and off the water to the individual circuits of sprinklers or drip emitters. Check valves allow the water to flow in only one direction. Master valves are located at the water source and turn on and off the water for the entire irrigation system when not in use.

Valve Zone   An area where the irrigation is all controlled by a single control valve. Each valve zone must be within only one hydrozone.


Water Meter   A device used to measure the quantity of water that flows through a pipe.

Water Table   The top of an underground aquifer or the "groundwater" level. Below the water table the ground is saturated with water.

Well   A ground-water source, usually a whole dug in the ground down to the water table. Some "wells" such as artesian wells are probably better classified as "springs".