How to Select the Best Filter for Your Drip Irrigation Systems
by Stuart Spaulding —
CLIA Certified Landscape Irrigation Auditor Training & Communications Manager at DIG Corp.
How to Select the Best Filter for Your Drip Irrigation Systems
Water Quality
Selecting the correct size and type of filter for a low-volume irrigation system is a critical decision that should be made with forethought and research. This process begins by acquiring knowledge of the quality of the water being supplied. Water sources for drip irrigation systems are varied and can include potable treated water, well water, recycled/grey water, pond/stream/river water, rainwater, and more. It is essential to know what primary contaminants are present in the water supply so the correct type of filter can be selected.
Filters are a vital component of the head assembly, and their function is to prevent emitters, drip lines, foggers, and micro-sprinklers from clogging by keeping the water supply clean and free of organic and inorganic contaminants. There are two main element types of Y filters available for use with landscape drip irrigation systems: screen and disc.
Screen Filters
The most common type are screen filters, which force the water through a cylindrical screen element. The foreign matter/debris accumulates on the inside of the removable screen element. The screen material can be polyester or stainless steel (preferably) and is available in a variety of mesh sizes. These filters are primarily designed to remove inorganic contaminants and hard particulates such as sand. Organic, non-solid contaminants can clog these screens quickly, and they can be quite difficult to remove from the screen material. These filters are usually readily available in sizes from ¾” to 2” and are equipped with a variety of element mesh sizes. Models with a manual flush valve allow for quick flushing of the screen element without removing it from the filter body. Most drip systems require a filter with a minimum of 120 mesh.
Disc Filters
A better choice if the water supply contains organic contaminants like algae or non-solid materials is the disc filter. Disc filters force the water through a set of stacked round discs, and the foreign matter collects on the outside of the disc set. Disc filters have a larger surface filtration area than screen filters and do an excellent job removing organic contaminants. These filters can be cleaned manually by removing the disc set from the filter body or by back-flushing it through the opened flush valve or cap.
Filter Sizing
Typically, the optimal filter inlet/outlet size is determined by (and equivalent to) the size of the adjacent system control valve (or supply pipe size). Pressure loss charts are available from the filter manufacturer and should be consulted prior to final selection to ensure the performance specifications are compatible with systemic flow rates and operating pressures. The filter inlet/outlet size must be large enough to match the system flow rate and not cause significant pressure loss. Larger filters usually have two pressure gauge ports available; however, all models should have a flush cap or valve where a pressure gauge may be installed to monitor/verify system operating pressure.
Maintenance
All drip system filters should be checked periodically and cleaned if and when necessary. Visually inspect the filter body for external leaks while the system is running. Unscrew and remove the filter cover to remove, inspect, and clean the screen or disc element. After cleaning with a brush under running water, re-install the element into the filter body and re-test. It is important to remember that landscape drip irrigation Y filters do not remove dissolved compounds, salts, or minerals commonly present in “hard” water.
