Pumps move the water (gallons
per minute) and bring it under pressure (pounds per square inch, psi).
meters measure how much water has passed a given point in the system.
Backflow preventers stop
water from flowing back to the source and carrying contamination back to the
source, i.e. a well. Backflow preventers often have a check valve, air vacuum
breaker, and low pressure drain as its' components.
A check valve is a one-way
flow device that allows water to pass in one direction but that closes if water
reverses direction. The valve has a gate inside that swings open in one direction
but is pushed closed by water flowing in the other direction.
An air vacuum breaker allows
air to enter the pipeline when there is no water pressure and thus prevents
a vacuum from being created to pull water pass a closed check valve. It also
allows air to escape when a water pipeline is being filled with water. A ball
is used to close the opening when the water rises to fill the device.
A low-pressure drain valve opens when the system pressure is very low to allow water to drain out. It is
used to drain any remaining water in a pipeline after the system is stopped
or to drain any leakage past a check valve.
Valves are used to turn
on or off the flow of water in the pipeline. Manual valves are typically gate
or ball valves that open fully to allow water to pass with a minimum of restriction.
A gate valve has a mechanical gate that is opened or closed by turning the knob
or handle. A ball valve uses a ball with a hole in it; the handle is turned
so the hole is in the direction of flow to allow water to pass. Electric solenoid
valves use 24-volt electric to hold an internal valve open; a time clock controller is used to operate the valve.
Filters are used in microirrigation
irrigation systems to prevent small particles of dirt or organic debris from
clogging the small orifices or outlets in the emitter devices.
The emitters are engineered
devices that control the water flow at some pressure. Some emitter devices are
pressure compensating which means a diaphragm moves with the pressure to adjust
water flow with pressure changes, so the water discharge is fairly uniform over
a range of pressures.
Fertilizer injection systems deliver dissolved or liquid fertilizer into the irrigation system when the water
is flowing. Sometimes other chemicals are injected to control other water quality
situations. A concentrated fertilizer solution is prepared for injection through
the fertilizer injectors. The injectors mix the concentrated fertilizer solution
into the irrigation water in some ratio, i.e. 1:200, to dilute the final solution
to a calculated parts per million (ppm) of nutrient, such as 200 ppm Nitrogen. The concentrated
solution would be 40,000 ppm N in this case.
(EC) and pH meters may be desired beyond the injection site to monitor the nutrient
levels in the irrigation water. Some of these pH and EC meters are designed to be housed in the main water pipe (in a greenhouse or hydponic setting), so that continuous monitoring of TSS and pH can be logged by a computer.
Pressure regulators act
on moving water to maintain a given pressure beyond the device. They can be
preset to specific pressures or adjustable to a range of pressures. Pressures
vary through the system and the regulator can help to provide irrigation zones
with the proper operating pressure.
Pressure relief valves are
designed to allow water to "blow off" to reduce pressure when sudden increases
in pressure occur within the system. Water hammer is a term that refers to a
sudden increase in pressure due to a valve being closed too quickly on fast
flowing water downstream. Water hammer can cause pipes and valves to burst so
it is avoided with proper design.