- Backflow Preventer
-
A device installed on an irrigation system to prevent water in the irrigation pipes from flowing back into the main (household) water supply. Irrigation systems come in contact with many potentially harmful materials including fertilizers, pesticides, bacteria, insects, and animal waste. These contaminates will pollute household water supplies if sucked back in via backflow.
Types of Backflow Preventers
Air Gap
An Air Gap is a backflow prevention system that prevents water from being sucked, or siphoned, back into the water supply. There is a physical space (vertically) between a discharge pipe and the flood-level rim of receiving vessel. The receiving vessel is open and not under pressure.
The air gap must be at least double the diameter of the supply pipe measured vertically above the overflow rim of the receiving vessel. The Air Gap must be 1 inch or greater.
While not always practical, an Air Gap provides the maximum protection available against backflow (and potential contamination of water supply).
Atomospheric Vacuum Breaker (AVB)
An Atmospheric Vacuum Breaker is a backflow preventer that is installed above the highest point in an irrigation system. It contains a float (air inlet valve) which closes when water is moving in the normal direction, keeping air out of the system. If a siphon begins to form, the float drops to allow air into the system, breaking any potential backflow into the main water supply. Atmospheric Vacuum Breakers should be installed at a minimum of 6" above the highest pipe or outlet in the system.
Double Check Valve Assembly (DC)
A Double Check Valve (or double check assembly) is a backflow preventer containing two positive-seating check valves assembled in series. A ball valve or gate valve is installed at each end for isolation and testing of each check valve. Small ball valves, called testcocks, provide locations for attatchment of testing equipment.
The benefit of the double check valve is that it does not need to be installed abouvr the highets head or pipe in the irrigation system. It can be installed underground in a valve box.
Pressure Vacuum Breaker (PVB)
A Pressure Vacuum Breaker (PVB) is a backflow device containing a spring loaded check valve and an independently operating air inlet valve. Since the PVB is not designed to protect aginast backpressure, it must be installed at least 12" above the highest head or pipe in the irrigation system. It provides a better solution against backsiphonage than an atmospheric vacuum breaker as the spring-loaded valve dows not rely on gravity as does the AVB.
Reduced Pressure Principle Assembly (RP, RPA, RPZ)
A Reduced Pressure Principle Assembly is a backflow device consisting of of two two independently acting check valves and a mechanically independent, hydraulically dependent automatic pressure differential relief valve located between the two check valves. The relief valve maintains a reduced pressure zone between the two check valves that is lower than the supply pressure. A ball valve or gate valve is installed at each end for isolation and testing of each check valve. Four small ball valves, called testcocks, provide locations for attatchment of testing equipment. The RP must be installed 12" above the highest head or pipe in the irrigation system.
- Drip Irrigation
-
Drip irrigation is a watering method which delivers water to plants slowly at the roots. It is also known as trickle or micro-irrigation. Where typical pop-up sprinklers spray water into the air and onto plants, drip irrigation systems combine flexible poly drip tubing and drip emitters (or drippers) to both conserve water and save money.
Drip systems are not affected by wind and will greatly reduce evaporation and runoff common with traditional irrigation systems. Drip irrigation is the perfect solution for raised beds, vegetable gardens, and potted plants. See also Emitter, Barbed Fitting, and Poly Pipe.
Learn how to plan, design, and install your own Drip Irrigation System with our FREE online Drip Irrigation Tutorials.
- Drip Tape
-
Commonly used by commercial growers, drip tape is a thin-walled dripline with inline emitters pre-installed at preset spacings. The tape is flat and expands when filled with water. It is a great product for row crops and vegetable gardens.
Drip tape fittings use a twisting mechanisim rather than compression or barbed fittings like conventional drip tubing.
- PSI
-
Pounds per Square Inch. A measurement of water pressure. One atmosphere is approximately 15 psi. See also Pressure, Dynamic Water Pressure, Static Water Pressure, Regulator.
- Water Hammer
-
When the velocity of water flowing in a pipe is very high and is subsequently stopped, water hammer may occur, creating an an audible thumping sound in the pipes. It is generally caused by a rapid cessation of flow (e.g. a valve is closed quickly). High-velocity water has a lot of kinetic energy (KE). When the water is stopped rapidly, the KE is converted to potential energy.
Velocity is increased as pipe wall thickness increases or the pipe is reduced in size.. Therefore, water hammer is more common in schedule 40 PVC pipe than the thinner-walled Class 200. Thinner walls are more flexible and will also absorb more kinetic energy than a rigid, thick-walled pipe. If the pipe has been sized too small (thus creating the higher velocity), a shock wave may be created when the valve shuts off quickly. See also Kinetic Energy, Water Hammer Arrester.
- Pressure
-
With respect to irrigation, pressure is a measurement of the force of water within an irrigation system or main line, usually expressed in pounds per square inch (PSI). It is the force that moves (or has the potential to move) water through valves, pipes, fittings, sprinklers and emitters.
Static Pressure is measured when the system is closed and no water is flowing through it.
Dynamic Pressure is measured when the system is open and water is flowing through. Flow and pressure affect each other.
Drip irrigation operates at pressure generally lower than most household water pressure.
See also Dynamic Water Pressure, Static Water Pressure, Regulator, Main Line.
- Pascal
-
A metric unit of measuring pressure. It equals a force of one Newton per square meter. A Newton is the force required to give a 1 kilogram mass an acceleration of 1 meter per second. Since the Pascal is a very small pressure, KiloPascals (kPa) are commonly used. One KPa equals one thousand Pascals. 101.325 KPa equals one atmosphere.
The Pascal is now widely used. This is the S.I. unit, and equals a force of one Newton per square metre (in turn, a Newton is the force required to give a 1 kilogram mass an acceleration of 1 metre per second per second.) The Pascal is quite a small pressure, so we often use KiloPascals (kPa), equal to one thousand Pascals. 101.325 kPa equals one atmosphere.
- KPa
-
A metric unit of measuring pressure. One KPa equals one thousand Pascals. 101.325 KPa equals one atmosphere.
One Pascal equals a force of one Newton per square meter. A Newton is the force required to give a 1 kilogram mass an acceleration of 1 meter per second. Since the Pascal is a very small pressure, KiloPascals (kPa) are more commonly used.
- Cavitation
-
Cavitation occurs when cavities or bubbles form in the liquid being pumped. Cavities are formed at the low pressure side of the pump (suction side). The bubbles or cavities move into areas of high pressure and implode or collapse on themselves. Water then moves at a high velocity as it contacts pump components. Noise increases and vibrations occur, damaging pump components.
Cavitation effects include:
* Increased noise and vibration
* Reduction of pump capacity
* Reduction of pump output pressure
* Drop in pump efficiency
- Back Flow
-
An unintended reverse flow of water from an irrigation system into the main water supply. It is caused by backpressure or a back siphon. Irrigation systems come in contact with many potentially harmful materials including fertilizers, pesticides, bacteria, insects, and animal waste. These contaminates will pollute household water supplies if sucked back in via backflow.
Backpressure can be created by a pump in the system or when pipe/sprinklers in the zone are at a higher elevation than the point of connection to the water source.
Back siphoning can occur if there is a break in the supply pipe and/or a drop in pressure of the supply line. Backflow most commonly occurs when there is a temporary sudden loss of pressure from the main water supply.
A properly installed backflow preventer will prevent backpressure or back siphonage from impacting the main water supply.
- Hose Thread
-
Officially called "Garden Hose Thread" (GHT), hose threads are found on garden hoses and many irrigation parts and adapter fittings. Generally referred to as "3/4" hose threads" the outer diameter is 1.0625 inches and has a pitch of 11.5 tpi (threads per inch). Hose threads are NOT the same as pipe threads and should never be screwed into pipe threaded fittings.
Male hose threads are found on the outside of a fitting and thread into female hose threads.
Female hose threads are found on the inside of a fitting and accept male hose threads.
Hose threads do not require Teflon tape or pipe dope (like pipe threads), just a hose washer. If you find a water leak with hose threads, it is most likely a worn hose washer. It may be time to replace it. Hose washers are found inside fittings with female hose threads. See also Pipe Thread, Adapter, Swivel, Hose Washer, Teflon Tape
- Pipe Thread
-
The common term for National Pipe Thread (NPT). Pipe threads require Teflon tape or pipe dope to create a water-tight seal. Do not thread together pipe threads and hose threads. See also Teflon Tape, Pipe Dope, Hose Thread.
- Teflon Tape
-
A non-adhesive tape (made of Teflon non-stick material) that is used to create a water-tight seal with pipe threaded fittings. It is tightly wrapped in a clockwise motion 3-4 times around the male pipe threads. Male and female fittings are then threaded together.
- Hose Washer
-
Rubber gasket found inside fittings with female hose threads that makes a water-tight seal. See also Hose Thread.
