Elements of
an Irrigation System
An automatic
irrigation system is a complex piece of equipment.
Anyone who has
ever attempted to take a shower while the washing
machine is filling or someone is washing a car outside
has already learned the first lesson of irrigation
design - there is only a finite amount of water available
for use at any given time. Because of this, it is
not possible to water the entire yard at once. The
yard must therefore be divided into smaller watering zones (sometimes
referred to as 'stations'), the size of which is
determined by the number of heads which can be run
simultaneously with the available water supply. Areas
grouped within a given zone should have similar watering
requirements, and lawn & garden should never
be mixed within a single zone.
24VAC electric
solenoid zone valves control the flow
of water to each zone. The valves receive signals
from the controller via
buried multi-strand low-voltage wire. Some valves
must be installed atop risers standing out of the
ground while others can be installed below ground
in durable fiberglass enclosures.
The controller (or timer)
is an electronic device which runs the irrigation
system. The time of day and days of the week that
the system will run, as well as the length of time
each zone will water, are programmable. Different
controller models have varying numbers of 'programs'
and start times. Each program acts like an independent
controller, allowing for different watering schedules
for different types of landscape (i.e. lawns vs.
gardens). The controller is usually located in the
garage or in a utility room, and must typically be
mounted within 5' of an electrical outlet. Sealed
outdoor models are also available. The CRD currently
offers a $100 rebate for upgrading from an obsolete
model controller to one capable of being programmed
for specific days of the week.
A rain
sensor is a simple adjustable device which
measures rainfall and prevents the irrigation system
from running when the prescribed amount of rain
has fallen. Amounts of sun and rain received can
be extremely variable in our climate in the spring
and fall (and sometimes even summer). Having a
rain sensor attached to the system means saving
water during rainy times without having to constantly
adjust the controller. It can be mounted on the
fascia or any other vertical surface, or it can
be threaded onto the top of a 1/2" riser in
the garden. The CRD currently offers a $50 rebate
for the installation of an approved rain sensor
as part of its ongoing water conservation strategy.
Backflow is
a phenomenon which occurs when a sudden drop in water
mains pressure (for example, when the city flushes
its fire hydrants in the spring) causes water to
be drawn back through the irrigation system into
the potable water supply. This creates an opportunity
for fertilizers and other chemicals in the soil to
contaminate the drinking water. Provincial and municipal
plumbing codes require mandatory backflow
protection on all underground irrigation.
The double check valve
assembly (DCVA) is a testable and repairable
unit which utilizes two positive seating check modules
to prevent backflow. This can also be achieved through
the use of atmospheric
vacuum breakers (AVB) or anti-siphon
zone valves. The DCVA provides a much higher
degree of protection than AVB type backflow preventers
and can be mounted below ground in an enclosure.
AVB's and anti-siphon valves must be mounted a minimum
6" above the of the highest system piping elevation.
Popup gear-driven
rotors rotate
to water large lawn areas. Fixed-arc
popup sprays spray a fixed pattern to
water small or irregular lawn areas. Popup heads
should be mounted on swing arms to
allow for easy future adjustment up or down and
should be installed so that the top of the head
(when retracted) is just below surface level, so
as not to interfere with lawn maintenance.
Garden areas can
be watered with shrub
sprays or preferably the more efficient micro-sprays which
can be mounted on permanent risers or attached to
1/4" tubing. Hedges and window boxes can be
watered with drip emitters or
1/4" to 1/2" emitterline.
Containers and hanging baskets are watered with adjustable
bubblers or drip emitters on 1/4" tubing.
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