AMIAD - AUSTRALIA & ASIA PACIFIC NEWS - VOLUME 9 - APRIL 2017 MARCH 2014 Vol.3 | Page 7

SUCTION

AUTOMATIC

FILTER SELECTION FOR IRRIGATION

|BY David Thompson –

SCREEN

Buisness Development - Irrigation Division at Amiad Water Systems

Selecting the correct filter can Table 1: Select the correct micron size for your screen based on the orifice
be a complicated task. It can being protected and the water type
be made a lot easier, however,
if you follow a number of
steps. David Thompson
outlines these steps in the
article and takes away some
of the mystery involved in the
process.
Step 1: Orifice size – what are
you protecting?
The first step in selecting a
screen filter is to properly
define the application; many
filters are under specified
because the application is not
properly considered.
In general terms, we are trying
to protect the smallest orifice in
the system; in drip sys tems it is
the dripper pathway or
regulating chamber and in a
sprinklers systems it is usually
the sprinkler nozzle that is the
smallest orifice. In some
Sprinkler systems it could be
other equipment in the system
such as the solenoid orifice in
the field control valve which will
have the smallest orifice which
will then need to be considered.
This means it is very important,
first, to determine your target
and, second, to select the
appropriate micron size screen
for your filter.

Step 2: Water Quality, Micron
Size and Filtration Ratio
The next step is to determine
the type of suspended solids in
the system. This can be divided
into two main categories Organic and Inorganic.
(Dissolved solids [TDS] are not
removed by mechanical
filtration and are not covered in
this article.)
PAGE 7 - March 2014

The relationship between the
type of water and the orifice size
to be protected form the next
stage of the selection process.
Table 1 is a guide to selecting
the correct micron size for your
screen based on the orifice you
would like to protect and the
type of water in your system.

It is very important to
consider the following factors:
• Pump Flow Rate and
Pressure
• Pump flow and Pressure
required including flush flow
• Pump flow and Pressure
required for filling of system
including filter flush

Step 3: System evaluation &
System Operation

Step 4: Minimum flow rates
and pressure during flush

Having selected the correct
micron size for the application it
is now time to check the
available performance from the
system.
Suction filters have a maximum
and minimum flow and pressure
requirement which need to be
considered. Suction Auto Filters
(SAF) work on the basis of return
flow of clean water from the
downstream of the screen
forcing the collected particles
into the nozzle system which is
connected to the scanner which
is in turn connect to the exhaust
valve.
The flow of water and its
pressure through the nozzle
system are critical for effective
operation. The stated Minimum
flow is the minimum amount of
water required to achieve
cleaning and is just as important
as the Maximum required flow
when designing a filter system.

Minimum flow rate and
pressure for the filter during
flush as stated relates to the
minimum amount of water
needed to ensure efficient
cleaning of the filter. It should
be remembered that this
minimum flow and pressure
can be on top of the system
flow unless a downstream
isolation valve or pressure
sustaining valve is used.
This means that it is
therefore necessary to check
the pump curve for the result
of continued irrigation and
flush at the same time. In
many cases the pump will
drop off its curve and not
delivery enough flow and
pressure during this critical
period.