Prepared by W. Bryan Smith, Area Extension Agent, Agricultural Engineer, Clemson University. (New 5/08.)
We normally do not filter irrigation water used with sprinkler systems. The large nozzle sizes (typically 7/64 inches and larger) will usually pass any particles or sediment in the water with little problem. Drip emitters and microsprayers, however, have much smaller outlets and pathways that can easily be plugged by small particles. The water provided to a drip system must be properly filtered.
A drip system requires a 150 “mesh” filter to prevent plugging problems regardless of type. “150 mesh ” means that 150 openings can be counted in a straight line in the filter screen over a one inch distance. Some emitters and microsprayers require an even smaller, 200 mesh screen. Don’t depend on common household “ sediment” filters to provide adequate protection. Purchase a filter with the proper “mesh” rating to protect your investment.
Figure 1. Typical filters.
(Photo credit: Bryan Smith)
Figure 2. A 150 mesh filter element.
(Photo credit: Bryan Smith)
There are two special problems that may cause difficulty for a drip system regardless of the filtration system used. The first is pond or surface water. Surface water naturally contains a large amount of sediment and organic matter. The high load of sediment can plug a normally-sized screen filter in a short time. Usually some type of self-cleaning screen filter or a sand media filter (similar to a pool filter) is used to prevent frequent plugging.
Surface water will also contain algae that may grow on the filter screen, causing frequent plugging problems. Usually a small but continuous injection of chlorine into the irrigation water will prevent algae problems. Chemical injection of any type requires certain safeguards to be installed in the irrigation system to prevent backflow into the water body. For a small drip system in a landscape it will be less expensive (and much more convenient) to use well or municipal water for the drip system and surface water for the sprinkler system.
The second potential problem for a drip system is iron in well water. The iron will remain in a liquid form and flow through the filter regardless of the filter mesh size. When the iron leaves the drip emitter or microsprayer and contacts the air, it will oxidize into iron oxide, which is a solid. In a normal sprinkler system with large nozzle openings this is not a problem, but iron oxide deposits will plug an emitter or microsprayer in a very short time.
If the homeowner suspects that iron is present in the well water to be used with a drip system, the first course of action is to have the water tested for iron. If the iron content is less than 0.1 parts per million there will not be a plugging problem. If the iron content is 0.3 parts per million or more there will definitely be a plugging problem. Test the water before installing a drip system if there are reddish-brown stains in the sink or tub.
Drip irrigation systems do not require as much pressure as a normal sprinkler system. Drip tubing and emitter systems work well with a pressure of 30 pounds per square inch (psi). A pressure of more than 40 psi can pop emitters out of the tubing and send them on a trip across the landscape.
Drip tape has a much thinner wall and requires only 10 psi for proper operation. A pressure above 15 psi can rupture the drip tape quickly.
Pressure regulators are used to protect drip systems from excessive pressure. A 30 psi pressure regulator will work well for most landscape drip irrigation systems, while a 10 psi regulator will work nicely for a drip tape system in the garden. Expensive brass pressure regulators found at most hardware stores are not necessary for these systems – a simple, plastic, pre-set agricultural irrigation pressure regulator works well and will cost 50% to 75% less.
Figure 3. Pressure regulators made by two different manufacturers.
(Photo credit: Bryan Smith)
Some homeowners use a partially-opened valve to restrict the pressure to their drip system instead of a pressure regulator. This may work well for a time, but eventually the homeowner turns the valve on just a bit too far – and pays the price. The homeowner may also not open the valve quite enough - which in turn does not provide enough pressure for the drip emitters to “seat” and begin regulating flow. In this case we once again have the first openings providing more water, with the last openings providing very little - just like a pipe with simple holes drilled into it. The small amount of money required to purchase a pressure regulator is well worth the investment.
Filters and pressure regulators are not required for sprinklers or spray heads, but are a must for drip emitters, microsprayers, and drip tape. These systems will not work properly without filtration and pressure regulation.
Adapted from the 2007 South Carolina Master Gardener Training Manual.
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