CLOGGING AND MAINTENANCE OF MICRO IRRIGATION SYSTEMS - Management, Performance, and Applications of Micro Irrigation Systems - page 89

TABLE 1 Effects of water quality parameters on emitter plugging potential.

Chemical property Low Moderate Severe

PH <7.0 7.0-8.0 >8.0

Bicarbonate (ppm) <100.0

Iron (ppm) <0.2 0.2-1.5 >1.5

Sulfides (ppm) <0.2 0.2-2.0 >2.0

Manganese (ppm) <0.1 0.1-1.5 >1.5

7.2.1 MAINTENANCE OF FILTERS
Filters are essential components of an SDI system and they remove suspended sol-
ids from the water. There are three main types of filters: cyclonic filters (centrifugal
separators); screen and disk filters; and media filters. It is common practice to install
a combination of filters to effectively remove particles of various sizes and densities.

7.2.1.1 CENTRIFUGAL SEPARATORS
These filters need little maintenance, but they require regular flushing. The amount of
sediment in the incoming water, the volume rate of water used, and the capacity of the
collection chamber at the bottom of the filter will determine how often and how long
the flushing valve needs to operate. The sediment can be released manually or auto-
matically. If it is done manually, the bottom valve of the filter should be opened and
closed at regular intervals. An electronic valve controlled by a timer can automatically
open the bottom valve. Automated operation of the valve should be checked at least
every other day during the season.

7.2.1.2 SCREEN AND DISK FILTERS
Small screen filters use a nylon strainer or bag, which should be removed and checked
periodically for small holes. The flush valve controls the flushing of the screen filter.
This can be operated manually or automatically. The screen filter should be flushed
when the pressure between the two pressure gauges drops 5 psi (one is located before
the filters and the other after them). Automatic filters use a device called a “pressure
differential switch” to detect a pressure drop across the filters. Other systems use a
timer, which is usually set by the operator. The flushing can be timed according to
the irrigation time and the quality of the water. The interval between flushing can be
adjusted to account for differences in pressures across the filters. Automated flushing
devices should be checked at least every other day on large systems.

7.2.1.3 SAND MEDIA FILTERS
With these filters the most important task is to adjust the restrictor backflush valve.
If the backflow rate is too high sand filter media will be washed out of the filter con-
tainer. If the backflow rate is too low contaminating particles will not be washed out
of the filter. Bacterial growth and the chemistry of the water can cause the sand media
to cement. Cementing of the media causes channels to form in the sand, which can al-
low contaminated water to pass unfiltered into the irrigation system. Chlorination can
correct or prevent sand media cementing.