Glossary of Irrigation Terminology

Here is a glossary of commonly used terms in the irrigation industry:

AMPERE or AMP – A unit of electrical current. The unit is used to specify the movement of electrical charge per unit time through a conductor.

APPLICATION RATE – The rate at which water is applied to the turf or ornamental plantings. Also refers to the amount of water applied to a given area in one hour. (See also: Precipitation Rate )

ARC – Describes how far around in a circular pattern a sprinkler will rotate or spray. (A sprinkler with a 90° arc would spray a quarter circle pattern.)

AS-BUILT PLAN – A complete plan of an installed irrigation system designating valve, sprinkler and controller locations, routing of pipe and control wire. The plan includes all changes to the original design that were completed during installation.

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BACKFLOW – The unwanted reverse flow of liquids in a piping system.

BACKFLOW PREVENTER – A device installed between the point of connection and the sprinklers that is designed to prevent the backflow of contaminated water into the potable water supply.

Types of backflow preventers include:

• Air gap – A backflow technique utilizing a physical separation or air gap between two piping systems or hydraulic devices.
• Atmospheric Vacuum Breaker (AVB) – An anti-siphon device that uses a disc float assembly to seal off the atmospheric vent when an irrigation lateral line is pressurized. The disc float falls, opening the atmospheric vent, allowing air to enter the system when the lateral line is shut off or when the pressure drops to atmospheric levels or below.
• Double Check (DC) – A device containing two inline, positive seating, independent spring loaded check valves. DC assemblies also include two shut-off valves and approved ball valve test cocks.
• Pressure Vacuum Breaker (PVB) – A device consisting of either one or two positive seating check valves and an internally force loaded disc float assembly, downstream of the check valves, installed as a unit between two tightly closing shut-off valves and fitted with properly located test cocks. The disc float assembly is force loaded (generally by means of a spring) to a normally open position, and allows air to enter the piping system when the line pressure drops to 1 psi or below. Since the disc float is force loaded, this device can be installed on the pressure side of a shut-off valve. However, it is designed to prevent back-siphonage only and is not effective against backflow due to backpressure.
• Reduced Pressure (RP, RPA, RPZ) – A device consisting of two positive seating check valves, and an automatically operating pressure differential relief valve internally located between the two check valves, installed as a unit between two tightly closing shut-off valves, and fitted with properly located test cocks. During normal operation, the pressure in the zone between the two check valves is maintained at a lower pressure than the supply pressure. If the zone pressure starts to approach the supply pressure, the differential pressure relief valve will automatically maintain a differential of not less than 2 psi between the supply pressure and the zone between the two check valves by discharging to the atmosphere. This device is effective against backflow caused by backpressure and back siphonage and is used to protect the water system from substances which are hazardous to health.
  

BACK PRESSURE – Increase of pressure in the downstream piping system above the supply pressure at the point of connection which would cause, or tend to cause, a reversal of the normal direction of flow.

BACK SIPHONAGE – Reversal of flow (backflow) due to a reduction in system pressure, which causes a negative or subatmospheric pressure to exist at a site in the water system.

BRACKISH WATER – Water polluted or contaminated by organic matter, salts or acids, or a combination thereof.

BUBBLER – A water emission device that applies water directly to the soil surface, or that throws water a short distance, on order of one foot, before water contacts the soil.

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C

CHECK VALVE – A small device allowing water to flow in one direction only. A check valve has a spring that will hold the valve closed, and will not allow water to flow until a preset pressure is achieved in the system. Check valves that are preinstalled in sprinklers, or field installed in the lateral line pipe, take advantage of this spring.

COEFFICIENT OF UNIFORMITY (CU) – A measure of the variability of water distribution (precipitation rate) in a specific irrigated area. Using a catchment test in an irrigated area, the CU is a comparison of the average precipitation of all catchments and the deviation from that average. (A perfect CU of 100 states that the system is very efficient and there is no variability of water distribution.)

CONTROLLER – Also known as a timer, the part of an automatic sprinkler system that determines when a valve will turn on and how long it will operate. The timer sends a low voltage signal to the valve, which opens for a predetermined amount of time allowing water to flow to the sprinklers.

CROP COEFFICIENT – Different plants have specific watering requirements. The crop coefficient allows for the expression of this variation in moisture needs.

CYCLE – Refers to one complete operation of a controller station.

CYCLE AND SOAK CAPABILITY – A feature in Hunter controllers that allows the controller to divide up station run time, allowing the soil sufficient time to absorb the water before continuing irrigation.

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D

DESIGN CAPACITY – Measured in GPM, the “design capacity” is the maximum amount of water available for use in an irrigation system. The available design capacity determines how many sprinkler heads may be in operation at the same time.

DISTRIBUTION UNIFORMITY (DU) – The evenness with which water is distributed over an irrigated area. DU is calculated using a catchment test. Divide the average reading of the lowest one-quarter of catchments by the average reading of all catchments, and multiply the answer by 100. An excellent DU percentage is 75% to 85%, while a good DU is 65% to 70%.

DIAMETER OF THROW (COVERAGE) – Average diameter of the area wetted by a sprinkler operating in still air.

DYNAMIC PRESSURE – Measure of water pressure with the water in motion (also know as working pressure).

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E

ELECTRIC VALVE – Automatic valve usually controlled by 24 to 30 volt (AC) current.

EVAPOTRANSPIRATION (ET) – The amount of water needed by a plant is the sum of the amount lost through the evaporation of moisture at the soil’s surface and the transpiration of the water through the plant. The daily evapotranspiration rate, or ET is used in scheduling the irrigation needs for plant material.

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F

FLOW – The movement of fluids, through pipe, fittings, valves or other vessels generally measured in Gallons Per Minute (GPM), Gallons Per Hour (GPH), Cubic Feet Per Second (ft3/s), Cubic Meters Per Hour (m3/h), Liters Per Minute (l/m), or Liters Per Second (l/s).

FRICTION LOSS – The amount of pressure lost as water flows through the water meter, pipe, fittings and valves of an irrigation system. As the velocity of water flowing through the system increases, the friction loss will also increase. These losses can be used to calculate the approximate dynamic (working) pressure at any given point of a system.

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G

GPM (GALLONS PER MINUTE) – A standard measurement of water flow. The available GPM (also known as design capacity) must be known before a sprinkler design can be completed. Sprinkler heads have different GPM requirements. The total GPM of all of the sprinkler heads on one zone should not exceed the available GPM.

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H

HEAD FEET (PRESSURE) – A measure of pressure expressed in feet of water. Equivalent to .433 PSI per foot of water.

HEAD-TO-HEAD – This phrase describes the correct placement of sprinkler heads. One sprinkler must be placed so that it will spray another sprinkler (or 50% of the adjusted diameter). This provides for complete coverage of the irrigated area.

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I

INTAKE RATE OR INFILTRATION RATE – The measurement of the speed that water moves into the soil.

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L

LATERAL LINE – Non-pressure pipe running from the valve to the sprinklers.

LOOPED CIRCUIT – A piping system, usually a main line, that closes back on itself in a loop, providing more than one path for the water to flow to the valve(s).

LOW HEAD DRAINAGE – Water left in the pipe after a valve is turned off that is gently flowing out of a low elevation sprinkler head.

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M

MAINLINE – Pressurized pipe running from the point of connection to the zone control valves.

MANIFOLD – A group of valves.

MASTER VALVE – A normally closed valve installed at the supply point of the main that opens only when the automatic system is activated.

MATCHED PRECIPITATION RATE – A system or zone in which all the heads have similar precipitation rates is said to have matched precipitation rates.

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N

NON-VOLATILE MEMORY – A feature in irrigation controllers that will retain the programmed information in electronic memory during a power failure, without the need for a battery.

NOZZLE – The final orifice through which water passes from the sprinkler or emitter to the atmosphere.

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P

PIPE DOPE – Common name for commercial products used to apply to pipe fittings to assist in the appropriate fit of the threaded joints.

PITOT TUBE – A small ell shaped tube which can be attached to a pressure gauge or other measuring device to measure the velocity head of water discharging from a nozzle.

POINT OF CONNECTION (P.O.C.) – Location where irrigation system is connected to a (potable) water supply.

POLY PIPE – Polyethylene pipe is a black, flexible pipe popular for lateral line use in areas susceptible to long freezes in the winter. Soil moves as it freezes, and because poly pipe is flexible, it will hold up to this movement while the more rigid PVC pipe may break. An insert fitting with a hose clamp or a compression fitting is used with poly pipe.

POTABLE WATER – Water that is of known adequate quality to be used for human consumption. Domestic or drinkable water. It can be used as a source of irrigation water if protection is provided to prevent contamination to the domestic supply. Once water enters an irrigation system it is no longer considered potable.

PRECIPITATION RATE – The speed at which a sprinkler or an irrigation system applies water. The common units of measure for precipitation rates are inches per hour or millimeters per hour.

PRESSURE – Measured with a pressure gauge and expressed in pounds per square inch (PSI), bars or kPa. It is the amount of energy available to move water through pipe, valves, sprinklers or other components. Static pressure is the pressure measured when no water is flowing through a closed system. Dynamic pressure is the pressure measured when the system is open, or water is flowing through the system.

PRESSURE AT THE HEAD – When manufacturers discuss pressure for sprinkler use or nozzle performance, they are referring to the dynamic pressure as measured at the base of the sprinkler head.

PRESSURE RATING – The estimated maximum internal pressure that can be continuously exerted in a pipe or container with a high degree of certainty that it will not fail.

PRESSURE REGULATOR – A device that regulates the available pressure to a preset maximum.

PROGRAM – Information the user enters into the controller’s memory that determines when the system will water. A program contains three pieces of information: what days to water, what time to start watering, and how long each zone will water.

PSI – Abbreviation for pounds per square inch.

PUMP – A mechanical device that converts mechanical forms of energy into hydraulic energy.

PUMP START CIRCUIT – The feature on an irrigation controller that allows a connection to be made through a relay, with the pump starter, so the starter will be energized when a watering cycle begins.

PUMP START RELAY – An electronic device that uses a signal current from the irrigation controller to actuate a separate electrical circuit to energize the pump starter.

PVC PIPE – Generally white in color, PVC (poly vinyl chloride) pipe is more rigid than black poly pipe, and requires the use of PVC solvents (glue) for connections. The pipe manufacturers also recommend the use of primer just prior to the application of the solvent to ensure a strong, watertight connection. PVC pipe can be used both as a mainline or as a lateral line.

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R



RADIUS OF THROW – The distance from the sprinkler head to the furthest point of water application.

RECLAIMED WATER – Water that has been collected after an original use for reuse.

REMOTE CONTROL – Device that can be used to activate electronic irrigation valves from a given distance away from the irrigation controller.

RESISTANCE – In electrical systems, it is the resistance to the flow of current. It can be compared to friction loss in an irrigation piping system. Resistance causes a drop in voltage along the length of a wire and is measured in ohms.

ROTORS – Gear-driven sprinklers that spray a solid stream of water and rotate slowly in a circular pattern.

RUN-OFF – Water that is not absorbed by the soil and turf to which it is applied. Run-off occurs when water is applied at too great a rate, or for too long a time.

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S

SCHEDULING – The procedure of establishing and implementing the time and amount of irrigation water to apply.

SCHEDULING COEFFICIENT (SC) – The SC is a measure of uniformity of water distribution in any specific irrigated area as it relates to the precipitation rate of the entire area. Stated another way, the SC is an indication of the additional sprinkler run time necessary to compensate for dry areas. In a catchment test, the average precipitation rate for all catchments is divided by the one lowest precipitation rate to establish the SC of the system. (A perfect SC of 1.0 states that all catchments in a zone fill to the same level.)

SPRAY HEADS – Sprinklers that emit a fan-type spray of small droplets of water. These heads generally have a radius of 19' and shorter.

SPRINKLER DISTRIBUTION PATTERN – Two-dimensional water depth-distance relationship measured from a single (or multiple) sprinkler head(s).

STATIC PRESSURE – The measurement of water pressure when the water is at rest in a closed system.

STATION – A circuit on an irrigation controller that can be programmed with a run time separate from other circuits and provides power to one or more remote control valves.

SWING JOINT – A combination of threaded pipe and fittings used between the pipe and sprinkler that allows movement to be taken up in the threads rather than as a sheer force on the pipe. Can also be used to raise or lower sprinklers to final grade without plumbing changes.

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T

TIMER – See “ controller .”

TRAJECTORY – The trajectory of a sprinkler is the measurement (in degrees) of the angle of the water projecting out from the sprinkler’s nozzle. A trajectory of 0° would indicate a flat projection of water out from the nozzle.

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U

UNIFORMITY – The evenness of precipitation over a given area.

UNION – A pipe fitting used to connect two lengths of pipe in such a way that neither has to be rotated.

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V

VALVE – A device to control flow. Valves used in pressurized systems include:

• Angle – A valve configured with its outlet oriented 90 degrees from its inlet.
• Automatic Control Valves (also called remote control valves) – These valves are used in conjunction with automatic timers and are a convenient and economical way of delivering water to lawns, plants, and gardens. Inline automatic control valves are usually installed underground in valve boxes, and anti-siphon automatic control valves are installed 6" to 12" above the highest sprinkler in the zone. Anti-siphon valves are a type of backflow preventer and are not approved in all areas.
• Ball – A valve with a single arm or lever that requires a quarter turn to turn on or off. This single action is convenient, but caution should be used and the valve should not be turned on or off too quickly, as damage could result. Ball valves have resilient seats and are a better choice than gate valves if they are to be frequently used.
• Drain Valve, Automatic – Spring loaded valve that will automatically open and drain the line when the pressure drops to near zero.
• Gate Valves – Valves that have a wheel type handle. Several turns of the handle are required to turn off a gate valve. Gate valves are most commonly used on mainline pipes with high water pressure or high water flow. Because several turns are required, they are easier to turn off and the potential for damage caused by water hammer is reduced. Gate valves have a brass to brass seat and are not recommended for frequent use.
• Globe – A valve configured with its outlet oriented 180 degrees from its inlet but having flow path with directional changes and a gasketed disk moving perpendicular to the flow path to open or close the valve.
• Hydraulic – An irrigation zone valve which uses small flexible tubes and water under pressure to provide the actuation signal from the controller to the valve. Requires special freeze protection in northern climates.
• Isolation – Any mechanical valve used to isolate a section of a piping system.
• Manual Control Valves – These valves are not as common as they once were. The manually controlled sprinkler system eliminates having to move a hose-end sprinkler around from spot to spot, but the user does not have the convenience of the automatic system. Usually manual control valves incorporate an anti-siphon type backflow preventer.
• Pressure Regulating – A valve designed to automatically provide a preset downstream pressure in a hydraulic system.
• Quick Coupling – A permanently installed valve which allows direct access to the irrigation mainline for use of hoses. A quick coupling key is used to open the valve.
• Remote Control – A valve which is actuated by an automatic controller by electric or hydraulic means.

VELOCITY – The speed at which water travels through a pipe. The designer should use caution when designing a system where the water velocity exceeds 5 feet per second (see “ water hammer ”).

VOLUME – Expressed in gallons per minute (GPM), gallons per hour (GPH) cubic feet per second (ft3/s), cubic meters per hour m3/h), liters per minute (l/m), or liters per second (l/s). Volume is used to describe either the amount of water available or the amount of water used.

VOLTAGE – Amount of electrical potential required to force one amp of current flow in a circuit against one ohm of resistance.

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W

WATER HAMMER – The surging of pressure which occurs when a control valve is suddenly closed. In extreme conditions, this surging will cause the pipes to vibrate or create a pounding noise. Water hammer is most commonly caused by fast closing valves and/or high velocity water flow.

WATER METER – A device used to measure the flow of water.

WATER WINDOW – The amount of time in a day that is available for irrigation to occur at a site.

WIRE – In an automatic sprinkler system, low voltage direct burial wire is used to connect the automatic control valves to the controller. The most frequently used wire for commercial applications is single strand, heavy gauge direct burial copper wire. (The larger the gauge number, the thinner the wire.) The most frequently used wire for the home sprinkler system is multi-strand. Color-coded, multi-strand sprinkler wire has several coated wires together in one protective jacket.

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Z