Drip irrigation filter selection
Which filters a drip system needs depends on where the water comes from and what it carries. A hydrocyclone takes sand out of well water; a sand media filter holds the algae in pond and canal water. Last comes a disk or screen filter as fine as the emitters ask, most often 120 mesh. Each stage is sized to carry 1.2 times the flow through it.
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A worked example
30 decares of open-field vegetables in Aksu. The water comes from an irrigation canal; it grows algae in summer and carries silt and sand. One valve zone draws 60 m³/h, watered with dripline. The grower wants the filters to wash themselves.
- Filter train hydrocyclone → sand media → disk filter, 120 mesh (130 µm)
- Capacity needed 60 × 1.2 = 72 m³/h
- Hydrocyclone one 4″, for 40–80 m³/h; sized for the flow itself
- Sand media filter two 48″ tanks, 58 m³/h each, 116 m³/h in all
- Disk filter two 3″ automatic disks, 50 m³/h each, 100 m³/h in all
- Filter loss for the pump sum 0.4 + 0.5 + 0.5 = 1.4 bar
[The example’s numbers and the filter capacities await Perge’s check.]
How it is worked out
First comes the order. If the water carries sand, the first stage is a hydrocyclone. If it carries algae or other organic dirt, a sand media filter comes next. The last, safety filter is a disk for water with organic dirt, and a screen for clean water and sandy well water. The emitter sets how fine it is: 120 mesh (130 µm) for dripline and drippers, 80 mesh (200 µm) for mini sprinklers.
Then the size. The sand media and the last filter are sized for 1.2 times the flow; a filter run at its limit clogs fast. A sand media tank filters about 50 m³ an hour for each square metre of sand, and there are at least two tanks, so one filters while the other backflushes. The hydrocyclone is sized for the flow itself: below its range, the water doesn’t spin and the sand stays in.
Automatic backflush is advised when the water has algae, or when the capacity needed is more than one 3″ filter takes (about 50 m³/h). For the pump, count each stage at its loss when it is due a wash: 0.4 bar for the hydrocyclone, 0.5 bar each for the sand media and the last filter.
Questions
Which filter does drip irrigation need?
It depends on the water. For sandy well water, a hydrocyclone with a screen or disk filter after it is enough. Pond, canal, stream and open reservoir water has algae, so it needs a sand media filter with a disk filter after it. Clean mains water needs just one screen or disk filter.
What does a sand filter do?
A sand media filter holds algae, fibres and organic dirt in a bed of sand inside the tank. It is the main filter for pond, canal and open reservoir water. There are at least two tanks, so one keeps filtering while the other backflushes. A disk filter goes after it as a safety filter.
What does a hydrocyclone do?
It spins the water so heavy sand drops to the bottom, and it is the first stage when well water carries sand. It doesn’t hold algae or organic dirt. Pick it by flow: below its working range, the water doesn’t spin fast enough to take the sand out.
What mesh should a disk filter be?
Dripline and drippers usually ask for 120 mesh (130 microns). Mini sprinklers do with 80 mesh (200 microns). The emitter’s catalogue gives the exact figure; the filter’s holes should be about 7 to 10 times smaller than the emitter’s narrowest water path.
How do I size a filter?
Take the most flow that will pass through it, which is one valve zone’s flow, multiply by 1.2, and pick a filter or a set of filters that carries that much. For a large flow, several filters go side by side on a manifold. A hydrocyclone is sized for the flow itself.
How often should a filter be washed?
Wash it when the pressure drop across it rises about 0.3 to 0.5 bar above the clean figure. With clean well water that can take weeks; with water full of algae, in summer it can be several times a day. That is why automatic backflush is advised for dirty water and large flows.