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.
