Key Irrigation Definitions
A comprehensive glossary of essential terms for the Texas Irrigator exam, covering pressure, flow, velocity, and more.
Absorption Rate
The rate at which a soil will accept water. Rate decreases as soil “capacity” is reached and is affected by soil type, slope, run-off, etc. It is also referred to as “percolation rate” or “infiltration rate”.
Actual Head Pressure (Dynamic Head Pressure)
Operating pressure at the base of the sprinkler head. Calculated by subtracting all pressure losses, between the head and the pressure source, from the static pressure at the source. It is also referred to as “dynamic head pressure” or “working head pressure”.
Air Gap
A complete physical separation between the free flowing discharge end of a potable water supply pipeline and an open or non-pressure receiving vessel.
Anti-siphon Device
Any device that introduces air into the system to prevent “back siphonage”. See definitions for atmospheric vacuum breaker or pressure-type vacuum breaker.
Application Rate (Precipitation Rate)
The rate at which water is applied by the irrigation system. It is usually measured in inches per hour. Often referred to as precipitation rate.
Arc
The surface area of the landscape to which the head will provide water. Usually described in degrees or part of a circle. For example, a 90-degree arc would be a quarter-circle sprinkler.
As-Built Plan
A corrected or redrawn plan (to scale) showing the actual location of all major components of the system and other information the property owner might require.
Atmospheric Vacuum Breaker (AVB)
An assembly containing an air inlet valve, a check seat and an air inlet port. The flow of water into the body causes the air inlet valve to close the air inlet port. When the flow of water stops the air inlet valves falls and forms a check against back siphonage.
Automatic Control Valve
An electric or hydraulic remote control valve in a sprinkler system that is activated by an automatic controller. Also called a section valve, zone valve or remote control valve.
Automatic System
An irrigation system which will automatically cycle according to a preset program.
Back Pressure
Any pressure, regardless of its source, against the outlet side of the backflow prevention device, which exceeds the supply pressure against the inlet side of the device.
Back Siphonage
A form of backflow due to negative or sub-atmospheric pressure within a potable water system.
Backflow
An undesired reversal of the flow of water in a piping system. Caused by back pressure or back siphonage.
Backflow Prevention
The mechanical prevention of reverse flow, or back siphonage, of non-potable water from an irrigation system into the potable water source.
Backflow Prevention Assembly
A pump that is installed on the water supply line and is designed to raise the operating pressure in the irrigation system.
Bushing
A pipe fitting used to change to either a larger or smaller size.
Check Valve
A valve that permits water to flow in one direction only.
Class Pipe
The Texas Commission on Environmental Quality.
Consulting
The act of providing advice, guidance, review or recommendations related to landscape irrigation systems.
Contour Line
A line of equal elevation drawn on a plan. For example, a contour line labeled “510” means that everywhere along that line is approximately 510 feet above mean sea level.
Control Wires
The wire that transmits the signals from the automatic controller to the automatic electric valves to open and close the valves.
Controller
An automatic timing device, which may be electro-mechanical, digital or a combination of both, and signals the automatic valves to open or close according to a prescribed program.
Council
The Texas Irrigator Advisory Council.
Cross-connection
An actual or potential connection between a potable water source and an irrigation system that may contain contaminates or pollutants, or any source of water that has been treated to a lesser degree in the treatment process.
Cycle
Refers to one complete operation of a controller through a watering program.
Design
The act of determining the various elements of a landscape irrigation system that will include collecting site specific information, defining plant watering needs, and conducting hydraulic calculations.
Design Pressure
The pressure that is required for an emission device to operate properly. Calculated by adding necessary operating pressure to the total of all pressure losses.
Direct Burial Wire
Any wire approved for direct underground burial without conduit.
Distribution Uniformity (DU)
The measure of the uniformity of irrigation water over an area. Expressed as a percentage and represents the major component of irrigation efficiency.
Diaphragm
The portion (flexible membrane) of an automatic valve that regulates the passage of water through the valve.
Double Check Valve Assembly (DCVA)
Backflow prevention assembly using two shut-off valves and two check valves assembled and pre-tested at the factory, designed to physically prevent the backflow of water.
Drain Valve
An automatic or manual valve used to drain water from a line after the system has operated.
Drip Irrigation
The slow application (low volume) of water, usually under low pressure, to the specific root zone area of the plant material.
Dry Line Shock (Dry Pipe Shock)
The shock occurring when a section valve is opened and the water travels unrestricted in empty lateral piping.
Dynamic Pressure
The pressure of water in motion.
Dynamic pressure is affected by changes in pressure caused by either elevation change or a pump, as well as by friction losses in pipe, valves, and fittings.
Emission Device
Any device that is contained within an irrigation system that is used to apply water, such as spray heads, rotary heads, or emitters.
Emitters
A mechanical device used in drip irrigation to limit water flow to a drip or slow trickle. Discharge rate is expressed in gallons per hour.
Evaporation
The natural process of changing water into vapor.
Evapotranspiration (ET)
The combination of evaporation and transpiration through plant material, used to measure water replacement needs.
Flow
The quantity of water moving through the system.
Flow is affected by: (a) the pressure available at the source, (b) the pressure losses from the source to the outlet or outlets, and (c) the size or number of outlet(s).
Flow Control Valve
A valve that can be mechanically adjusted to restrict water flow.
Flow Restrictions
Physical restrictions in component parts of an irrigation system that affect the flow of water thus causing a pressure loss.
Flush Flow
The higher initial momentary flow through a drip or trickle system required to flush emitters before pressure compensation occurs.
Feet of Head (Foot-Head)
A measure of pressure equivalent to .433 psi and equal to weight of 1 foot of water on a one square inch surface.
Friction Loss
A term used to identify pressure losses caused by water turbulence.
Friction loss is affected by: (a) velocity, (b) pipe inside diameter, (c) roughness of the inside of the pipe, and (d) length of the pipe.
Gate Valve
Manual valve capable of permitting full open flow resulting in very low friction loss. Uses a wedge type metal-to-metal gate or disk.
Globe Valve
A valve that uses a rubber or composition plug against a valve body seat to restrict or stop the flow of water.
Gauge (Wire)
Standards used for wire sizing. The larger the gauge number, the smaller the wire.
Head Spacing
The spacing between sprinkler heads.
Head to Head Spacing
Spacing of heads that is equal to the published radius.
Health Hazard
A cross-connection with an irrigation system involving substances that may cause death, illness, or disease if introduced into the potable supply.
Hydraulics
The science of dynamic and static water; the mathematical computation of determining pressure losses and requirements.
Hydraulically Controlled
A system using water pressure through tubing to operate remote control valves.
Insert Fittings
A fitting that fits into pipe or tubing, usually used on polyethylene pipe.
Irrigation Inspector
A licensed official who inspects irrigation systems and performs enforcement duties for a municipality or water district.
Irrigation Plan
A scaled drawing of a landscape irrigation system which lists required information and project scope.
Irrigation System
An assembly of parts permanently installed for the controlled distribution and conservation of water for landscape vegetation or erosion control.
Irrigation Technician
A person who works under a licensed irrigator to install, maintain, or repair irrigation systems.
Irrigation Zone
A subdivision of an irrigation system with a matched precipitation rate based on plant type, microclimate, and soil.
Irrigator
A person licensed to sell, design, consult, or supervise the installation and maintenance of irrigation systems.
Irrigator-in-Charge
The irrigator responsible for all irrigation work performed by an exempt business owner, including permits and design plans.
Landscape Irrigation
The science of applying water to promote and/or sustain growth of plant material or turf.
Lateral Piping
The piping after the remote control valve that is not subject to constant main line pressure.
Loop Mainline
A mainline designed to provide water to any valve from two or more directions.
Mainline
The portion of piping, normally under constant pressure, located between the water source and remote control valves.
Maintenance Checklist
A document for the owner containing information regarding the operation and maintenance of the irrigation system.
Manual System
An irrigation system where control valves are operated manually.
Master Valve
An automatic or manual valve installed at the supply point, which controls water flow into the system main line piping.
Matched Precipitation
All heads discharge varying amounts of water, combining to produce uniform coverage (e.g., a half-circle head discharging half the GPM of a full-circle).
Multiple Programming
The feature on some automatic controllers that allows more than one watering schedule or program.
Non-Health Hazard
A cross-connection involving substances that are aesthetically objectionable or a nuisance but not a danger to health.
Non-Potable Water
Water not suitable for human consumption.
Normally Closed Valve
An automatic valve through which no water will flow unless external influences are applied to open it.
Normally Open Valve
An automatic valve through which water will flow unless external influences are applied to close it.
Nozzle Tree
Refers to the interchangeable nozzle assortment, with different GPM and radii, provided with many rotor heads.
Pass-Through Contract
A written contract between a builder and a licensed irrigator to perform irrigation services.
Potable Water
Water suitable for human consumption.
Precipitation Rate
Also known as application rate. The rate at which water is applied, usually measured in inches per hour.
Pressure Compensating
A method of maintaining a constant discharge pressure regardless of inlet pressure.
Pressure Loss
The loss of pressure under flow conditions caused by friction or elevation.
Pressure Rating
A method of controlling the wall thickness of PVC pipe so all sizes in a class have the same pressure rating.
Pressure Relief Valve
A valve that will open when the inlet pressure exceeds a pre-set pressure.
Pressure Vacuum Breaker (PVB)
An assembly containing an independently operating check valve and a loaded air inlet valve.
Pump Circuit
An optional switch on controllers that energizes a pump when operation begins.
Quick Coupler Key
A bronze tube with a handle which inserts into a quick coupling valve for supplemental water.
Quick Coupling Valve
A constantly pressurized valve set vertically in the ground to provide supplemental water when a key is inserted.
Reclaimed Water
Treated domestic or municipal wastewater suitable for beneficial use like landscape irrigation.
Record Drawing
A drawing of an installed system showing locations of major components either to scale or with dimensions.
Reduced Pressure Principle Backflow Prevention Assembly (RPBA, RP, RPZ)
An assembly containing two check valves and a pressure differential relief valve; required if chemicals are added.
Saddle
A type of fitting which attaches around the pipe to furnish water to a threaded outlet.
Schedule Pipe
A classification system for pipe that has the same physical dimensions as iron pipe.
Section of Heads
A group of sprinklers controlled by one valve. Also known as a zone.
Sleeves
Piping or conduit under hardscape provided for irrigation system piping or wiring.
Slip Fitting
A smooth wall fitting solvent welded to PVC pipe rather than threaded.
Slope
A measure of the rate of change of elevation over a prescribed distance (Rise ÷ Run).
Soil, Types of
The three basic types are Sand, Silt, and Clay. Water moves through them via capillary action and gravity.
Solvent
A material that causes a partial dissolving of PVC pipe and fittings so a chemical fusion occurs.
Solvent Welding
The act of chemically fusing pipe and fittings together using solvent.
Static Pressure
The pressure of water at rest.
Static pressure is affected by elevation change or by the force of a pump. For each 1 ft. of elevation change, static pressure (or dynamic pressure) changes by 0.433 PSI.
Surge
An energy wave in pipe lines caused by excessive velocity of flow or sudden valve closure.
Swing Joint
A flexible joint connecting a sprinkler head to a pipe to provide protection from damage.
Threaded Fitting
A fitting that has IPS threads to receive a standard pipe thread or fitting.
Transpiration
The process of plant material giving off water vapor from the leaves.
Triangular Head Spacing
Spacing where heads are offset to form an equilateral triangle.
Valve-In-Head
Indicates that the automatic control valve is part of the sprinkler.
Velocity Head
The amount of pressure required to generate a specific velocity. This is the amount of energy or pressure that is used to make the water move at a given velocity.
Velocity (of water)
The speed at which water is moving.
Water Hammer
A shock wave in piping created by excessive velocity and a fast-closing valve.
Water Schedule
The procedure of establishing the time, frequency, and amount of irrigation water application.
Water Window
An allotted time available for watering, usually within a 24-hour period.