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.

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.

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.

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).