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A spinning device with cups mounted on a pole that measures wind speed.

Application Rate
The rate at which water is applied to the landscape by the irrigation system, and measured in inches applied per hour.

Arc of Coverage
The portion or degrees of a circle wetted by a single sprinkler head. A 90 degree arc represents a quarter circle, 120 degree arc is a third of a circle, and 180 degrees a half circle.

As-Built Drawing
A record of the location, with dimensions, of the installed irrigation system equipment. Changes in sprinkler head and lateral line locations are shown but not dimensioned. As-Built Drawings are provided by the installer.

Atmospheric Pressure
is the pressure exerted in every direction at any given point by the weight of the earth’s atmosphere. Increased altitude and storms will cause a reduction in atmospheric pressure. At sea level atmospheric pressure is equivalent to 14.7 psi or 33.9 feet of head.

Available Water Holding Capacity (AWHC) The water holding capacity or field capacity of a soil type is defined as the amount of water that remains in the soil after the gravitational water has drained away and after the rate of downward movement has decreased to a significant extent. Varies with soil type.

Backflow Preventer
A mechanical device installed at the beginning of the system to prevent a reverse water flow and contamination of the potable water supply. Reduced pressure backflow preventers, pressure vacuum breakers, and double check valves are the most common types used in the irrigation industry.

The rapid creation and disintegration of vapor bubbles that occurs when the pressure on the water is less than the vapor pressure. This usually occurs in a centrifugal pump at the impeller. When water enters the eye of the impeller an increase in velocity takes place accompanied by lower water pressure.

Check Valve
A device that prevents a reverse water flow in pipes and sprinkler heads. Commonly used in sprinkler heads to prevent low head drainage.

Control Valve
An electrically actuated valve used to operate each zone of the irrigation system.

An electric timing device that operates each zone for a predetermined time and frequency.

The extent of covering by sprinkler heads with respect to proper head spacing.

Crop Coefficient
ET is usually based on a field crop such as alfalfa, and a crop coefficient or percentage is used to determine the specific plant water requirement.

An interval of time during which the irrigation system is operated for one sequence of a regularly recurring succession of watering events. Also refereed to as "repeat cycles" and used to prevent runoff.

Used as a basis for anticipating practical problems and solving them at the planning stage and to create a drawing showing the location, type, and size of the irrigation system components prior to installation.

Distribution Uniformity
A method of calculating system uniformity and is measured as a percentage which indicates how closely the driest area compares to the average precipitation rate of the irrigated area.

Drain Valve
A valve used to drain the irrigation system for repairs or freeze protection. Referred to as "Manual Drains" or "Automatic Drains".

Drip Emitter
A small device emitting a dribble of water at very low pressure with flows measured in gallons per hour.

Dynamic Pressure
The pressure at any point in the irrigation system when the system is functioning. Measured with flow in the line.

The change by which water is converted from a liquid state into and carried off in vapor into the atmosphere.

Evapotranspiration (ET)
The amount of water lost from the soil both by evaporation from the surface and from transpiration from the plants growing thereon.

Field Capacity
Maximum water holding capacity of the soil which is usually measured in inches of water per inch of soil of soil depth.

Flow Sensor A device that measures the rate of water flow in the system in gallons per minute (GPM).

Friction Loss
Water rubbing against the system components resulting in accumulated pressure loss from the source to the nozzle.

Friction Head
Friction loss measured in head of feet.

Gallons Per Minute (GPM)
A measurement of the quantity and flow rate of water.

Another method of calculating pressure in feet of head instead of psi (one foot of head equals 0.433 psi).

Infiltration Rate
The rate in inches per hour that water moves into the soil. This rate slows with time.

Irrigation Efficiency
The percentage of water applied that is actually used by the plant.

Piping between the control valve and the sprinkler head.

Low Head Drainage
where water drains partially or completely out of the lateral line through the sprinkler head after each irrigation cycle is completed.

The piping upstream of the control valve.

Management allowable depletion (MAD)
The percentage of water at field capacity which can be removed from the soil by the plant prior to reaching the wilting point, at which time irrigation should occur.

Master Valve
A control valve installed at the beginning of the system which opens only during operation of the system.

Matched Application Rates
When all sprinkler heads within a zone, regardless of the arc of coverage, have approximately the same application rates.

Net Positive Suction Head Required
The suction head or pressure required at the eye of the impeller to ensure that the liquid will not boil under the reduced pressure and the impeller will operate without cavitation.

Net Positive Suction Head Available
The suction head or pressure that is available at the eye of the impeller after head losses, elevation differences, and vapor pressure are subtracted from the site atmospheric pressure.

A short duct that is used to direct the flow of water from sprinkler heads.

Operating Pressure
The pressure at any point in the irrigation system when the system is functioning. Measured with flow in the line.

The slow passage of water downward through the soil.

Polyvinyl Chloride (PVC)
A type of plastic used in the manufacturer of pipe, fittings, and other system equipment.

Polyethylene (PE)
A type of plastic used in the manufacturer of pipe, fittings, and other system equipment.

Potable Water
Water suitable for drinking.

Precipitation Rate
The quantity of rainfall deposited on the earth and measured in inches per hour. Also used in lieu of "Application Rate".

Pressure (PSI) The force that moves the water through the system and is measured in pounds per square foot or feet of head. One foot of water depth equals .433 PSI and one PSI equals 2.31 feet of head.

Pressure Gauge
A gauge used for indicating water pressure.

Pressure head
The operating pressure in feet of head required at the sprinkler head. Pressure Line See mainline.

Pressure Loss
See friction loss.

Pressure Reducing Valve
A device used to reduce water pressure.

Pressure Vacuum Breaker
See backflow preventer.

Quick Coupler Valve
A device attached to the system mainline which is activated by inserting a key attached to a sprinkler head or hose. Used for supplemental water.

Rain Shut-off Device
Accumulates rainfall and interrupts the irrigation cycle once rainfall exceeds a predetermined amount.

Reduced Pressure Backflow Preventer
See backflow preventer.

Repeat Cycles
See Cycles.

An upright piece of pipe used to support nozzles, heads, emitters, backflow preventers, and valves.

Root Zone
The depth of the plant root zone in the soil.

Scheduling Coefficient
A method of uniformity which relates the lowest precipitation rate in an area to the average precipitation rate, without regard to the size of the area, as is measured in the DU calculation. A Scheduling Coefficient value of 2.0 indicates the driest area is 2 times as dry as the average of the entire area.

A piece of pipe installed under paved areas to accommodate irrigation system pipe and wiring and used for ease of replacing equipment.

Soil Moisture Sensor
A device used to monitor the amount of water in the soil.

The electrical device on a control valve that actuates a plunger to open the valve.

Solvent Welded
A chemical substance used to dissolve the outer surface of PVC pipe and the inside of fittings, blending them as one.

Distance between sprinkler heads.

Sprinkler Head
A device used to spray water on lawns and landscapes.

Static Discharge Head
The elevation difference between the impeller eye and the sprinkler orifice.

Static Pressure
An indication of the amount of force available to operate the irrigation system. Measured with no flow in the line.

A position in the controller that activates a certain zone.

Sub-Surface Drip Irrigation
Usually pipe with drip emitters installed at 12 to 24-inch intervals inside the pipe, or in the wall of the pipe. These pipes are installed 12 to 24-inches apart, and at 4 to 6-inch depths.

Suction head
Occurs when the water level is higher than the impeller eye.

Suction lift
Occurs when the water level is lower than the impeller eye.

Waves of high and low water pressure moving through the pipes. Also, see water hammer.

Swing Joint
Fittings between the pipe and head that are used to absorb surface impact of the head and prevent breakage.

Tensiometers A device to determine the water content of the soil by measuring the tension or vacuum as water is removed from the soil.

The process of water moving through the leaf surface and vaporizing, and is utilized by the plant to cool its leaves.

Total head
All of the various heads that affect the pumps ability to produce pressure at a given flow rate.

Total Static Head
The difference in elevation between the water source and the point of discharge.

High uniformity occurs when the same amount of water is applied to each square foot of turf or landscape. The uniformity of rainfall is 96 percent without wind. 50 percent uniformity is common in older systems.

Vapor pressure
The pressure at which water will change to vapor (boil) at a certain temperature. The vapor pressure of water increases with temperature and reduces the available pressure at the pump suction.

The rate of water flow calculated in feet per second (FPS).

Velocity Head
The energy required to attain a certain velocity. The higher the velocity the greater the velocity head. Velocity head is usually insignificant in most landscape irrigation applications, but should be calculated where low pressure and high velocities occur.

Water Hammer
A series of water surges in piping caused by a fast closing valve. The magnitude and frequency is dependent on the velocity of flow, size, length and material of the pipe.

Wire Gauge A standard method of sizing wire diameter. The smaller the number the larger the diameter of the wire. #12, #14, and #16 gauge wire is commonly used in the irrigation industry.

Wilting Point
When the plant can no longer pull water from the soil. Zone An area covered by a group of heads connected to a control valve.

An area covered be a group of heads connected to a control valve.