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Irrigation Glossary


valve: Device to control flow. Valves used in pressurized systems include:

  • alfalfa: Outlet valve attached to the top of a short vertical pipe (riser) with an opening equal in diameter to the inside diameter of the riser pipe and an adjustable lid or cover to control water flow. A ring around the outside of the valve frame provides a seat and seal for a portable hydrant. Typically used in border or basin irrigation. (ANSI/ASAE S261.7 OCT96;  NRCS, 1997) 
  • angle: Valve configured with its outlet oriented 90 degrees from its inlet. 
  • air vent (air relief, air release): Device that releases air from a pipeline automatically without permitting loss of water. (NRCS, 1997) 
  • air vacuum, air relief: Device that releases air from a pipeline automatically without permitting loss of water or admits air automatically if the internal pressure becomes less than atmospheric. (NRCS, 1997) 
  • back flow prevention: Check valve that allows flow in one direction.  ...  (NRCS, 1997) See specific valve for details. 
  • ball: Valve in a pipeline used to start or stop flow by rotating a sealed ball with a transverse hole approximately equal to the diameter of the pipeline. Ball rotation is typically 90 degrees for a single-port control ...  (NRCS, 1997). Valve with an internally mounted ball with a hole in the center for water to pass through. (Rotation of the ball one-fourth turn opens and closes the valve.)  (Rochester, 1995) 
  • butterfly: Valve in a pipeline to start or stop flow by rotating a disk 90 degrees. The disk is about the same diameter as the pipeline. ... (NRCS, 1997) 
  • check: Valve used in a pipeline which allows flow in only one direction. (NRCS, 1997) 
  • chemigation: Valve especially designed to be used with the injection of chemicals in an irrigation system. 
  • corporation stop: Quarter turn valve similar to a ball valve with two exceptions. Internally there is a circular disk rather than a ball, and there is no attached handle. (Rochester, 1995) 
  • curb stop: Physically the same as corporation valve but used at a different location. 
  • drain valve
  • automatic: Spring loaded valve that automatically opens and drains the line when the pressure drops to near zero. (NRCS, 1997) 
  • flushing: Valve on the end of a line to flush out dirt and debris.  May be incorporated into an end plug or cap. (NRCS, 1997) 
  • float valve: Valve, actuated by a float, that automatically controls the flow of water. (NRCS, 1997) 
  • foot valve: Check valve used on the bottom of the suction pipe to retain the water in the pump when it is not in operation. (NRCS, 1997) 
  • flow control: Valve with automatically adjusts to provide a predetermined downstream flow. 
  • gate: Valve in a pipeline used to start or stop water flow.  May be operated by hand with or with mechanical assistance or by high or low voltage (solenoid) electric controlled mechanical assistance. Gate valves consist of seated slide or gates operated perpendicular to the flow of water. Head loss through a gate valve is typically less than a globe valve, but more than a ball or butterfly valve. (NRCS, 1997) 
  • globe: Valve in a pipeline used to start or stop water flow. Globe valves stop flow by positioning a disk and gasket over a machined seat about the same diameter as the pipe. Globe valves are limited to smaller sizes because of the high velocities and very high head loss through the valve. (NRCS, 1997) 
  • hydraulic: Irrigation zone valve which uses small flexible tubes and water under pressure to provide the actuation signal from the controller to the valve. 
  • isolation: Any mechanical valve used to isolate a section of a piping system. 
  • master: Valve used to protect the landscape from flooding in case of a ruptured main or malfunctioning downstream valve. The master valve is installed on the mainline after the backflow preventer (in some systems).  (Rain Bird, 1997) 
  • orchard: Outlet valve installed inside a short vertical pipe (riser) with an adjustable cover or lid for flow control. Similar to an alfalfa valve, but with lower flow capacity. Typically used in basin irrigation. (ASAE, 1998) 
  • pilot: Small valve used to actuate a larger one. 
  • pressure regulating: Valve designed to automatically provide a preset downstream pressure in a hydraulic system. 
  • pressure relief: Spring loaded valve set to open at a pressure slightly above the operating pressure, used to relieve excessive pressure and surges.(NRCS, 1997) 
  • pressure sustaining: Valve designed to provide a minimum preset upstream pressure. 
  • quick coupling: Permanently installed valve which allows direct access to the irrigation mainline. A quick coupling key is used to open the valve. (Rain Bird, 1997) 
  • remote control: Valve which is actuated by an automatic controller by electric or hydraulic means. Synonymous with Automatic Control Valve. (Rain Bird, 1997) 
  • surge: Device in a pipe T fitting to provide flow in alternate directions at timed intervals. Used in surge irrigation. (NRCS, 1997) 
  • swing check: See check. 
  • vacuum relief valve: Valve used to prevent a vacuum in pipelines and avoid collapsing of thin-wall pipe. (ASAE, 1998)

valve-in-head sprinkler: See sprinkler head.
vapor pressure (head): See head.
velocity*[V,v] {ft/s, fps, m/s} (11/6/99)Usually refers to the average velocity computed as flow rate per unit area of a pipe. Is the speed at which water moves through the system (pipe). (Monroe, 1993)
velocity head: See head.
vertical turbine pump:> See pump.
voids ratio {-}: Ratio of the volume of voids (pores) to the volume of soil. (Hess, 1999)
voltage* [V] {volt}  (11/6/99):

  • Force required to push and pull a stream of electrons through a circuit. (Derryberry, 1994) 
  • Amount of electrical potential required to force one amp of current flow in a circuit against one ohm of resistance. (Reference Manual, ch. 5)

volute: Refers to the flow path of water and its associated pump casing as it leaves the impeller of a pump.
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Water allotment [WA] {ccf, m3}: A method to accurately and fairly estimate a total volume of water that should be allocated to a site. (Predicting, 2000)
Water allotment adjustment factor [Kwa] {-}: Factor used in the equation to predict Water allotment. (Predicting, 2000)
water application efficiency: See efficiency.
water content (of soil sample): See soil-water content
water conveyance efficiency: See efficiency.
water hammer {psi, kPa m}:

  • Phenomenon which occurs when the velocity of water flowing in pipelines is rapidly changed, usually by a rapid or sudden gate or valve closure, starting or stopping of a pump, or sudden release of air. The resulting pressure waves pass through the water at high velocities and can produce very high momentary positive and/or negative pressures. ANSI/ASAE S261.7 OCT96) 
  • Shock wave created when the flow of water in a piping system suddenly stops (or changes speed). Usually the result of a fast-closing (or opening) valve. (Rain Bird, 1997)

water pressure: See pressure.
water holding capacity {in./in., in./ft, mm/m }: Total amount of water held in the soil per increment of depth. It is the amount of water held between field capacity and oven dry moisture level. (NRCS, 1997)
water horsepower (water power): See horsepower.
water meter: Device used  to measure to flow of water.
water rights: State administered legal rights to use water supplies derived from common law, court decisions, or statutory enactments. (NRCS, 1997)
water storage efficiency: See efficiency.
water table: Upper surface of a saturated zone below the soil surface where the water is at atmospheric pressure. (NRCS, 1997)
water use efficiency: See efficiency.
water window {h }: Time of day available for irrigation to occur. (Rain Bird, 1997)
weir: Flow measuring device for open-channel flow.  Weirs can be either sharp-crested or broad-crested. Flow opening may be rectangular, triangular, trapezoidal (cipolletti), or specially shaped to make the discharge linear with flow depth (sutro weir). Calibration is based on laboratory ratings. (NRCS, 1997)
wet weight (of soil sample)* [WW] {lbs, grams} (11/6/99)Weight of soil sample and included soil moisture. (Reference Manual)
wetted area* [As, WA] {ft 2, m2}: Surface area wetted at completion of irrigation. (Landscape, 1996)
wetted diameter: Preferred term diameter of throw.
wetting agent: Chemical used to reduce the surface tension of a liquid causing it to make better contact with the desired target.
wilting point [WP]: See permanent wilting point.
winterization: Process of removing water from the irrigation system before the onset of freezing temperatures. (Rain Bird, 1997)
wire gauge {-}: (One of several) standard units of measure for wire size. The larger the gauge number, the smaller the wire. (Rain Bird, 1997)
work* {hp-h, kw-h}: Work done by a force on a particle is defined as the product of the magnitude of the force and the distance through which the particle moves. (Physics, 1962). In hydraulic systems, it can be calculated as the product of the pressure and flow rate.

  • brake: Measure of work input into a pump or other device 
  • water: Measure of work output from a pump.

working pressure {psi, pKa}: Pressure of the irrigation system during operating.  Synonymous with dynamic pressure. (Rain Bird, 1997)
working storage [WS] {in., mm}: Amount of water available in the soil profile for plant use after consideration of MAD.  (Landscape, 1996)  Preferred term is Allowable Depletion [AD]
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zone: Section of an irrigation system served by a single control valve.  Zones are comprised of similar sprinkler types and plant material types with similar water requirements and types. (Rain Bird, 1997)