So which filter to use? There is no fixed answer. Your budget, water quality, and availability of filters and parts must all be considered. Screen filters are generally the least expensive. If you have a city water supply with nothing more than a periodic grain of sand or flake of rust in it, a screen filter will be fine in most cases. Sometimes a combination of more than one type of filter will be needed. For a smaller size system a disk filter would remove both sand and organics, but you might need to frequently clean it! Here are some suggestions based on the source of your irrigation water:
How much Filtration do you need?
What we are asking here is what's the smallest size of particle that needs to be removed from the water by the filter? The amount of filtration you need is dependent to a large degree on what type of irrigation you have. For example, drip irrigation systems need a much higher degree of filtration in order to protect the emitters from plugging. For most applications the amount of filtration is measured by the "mesh size" of the screen or maximum size in "microns" of an object that can pass through the filter.
You always want to use the highest level of filtration that is practical. Even if your sprinkler system can easily handle a fairly good size grain of sand without clogging, removing that sand grain is still advantageous, as it will eliminate the wear on the system caused by the sand grain as it passes through. The balancing factor is that the more particles removed the more often the filter clogs up and needs to be flushed. Excessive flushing can waste water and energy, so a trade off is necessary.
Here are some rule of thumb guidelines that I use:
Sprinkler systems A 60 mesh filter will remove most particles capable of plugging a sprinkler nozzle, however, I like to use a 100 mesh (150 micron) and often use a 150 mesh (100 micron) filter in order to also remove the particles that can cause wear on the system and damage the valves (higher mesh, higher is the head loss).
Bottom line- I would suggest using at least a 100 mesh (150 micron) screen or equivalent in the filter.
Micron and Mesh
While the Micron is a standard metric measurement, the term Mesh is rather subjective, especially for values over 300. For example, I've seen both 500 mesh and 700 mesh screens that have equal filtration, that is they both filter particles down to 30 microns. The problem is related to the size of wire from which the screen is manufactured. The mesh designation is based on the number of wires in one linear inch of the screen. So two screens can have the same mesh, but if one is made with thicker wire than the other, the one with thicker wire will have smaller openings between the wires. Therefore, micron is a much more accurate measurement for use in determining the size of particle that can (or can't!) pass through a filter.
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