As most landscapers in the Grand Valley know, filtering the ditch water from the dirty Colorado or Gunnison Rivers is part of the business. While most, if not all, irrigation systems here have some form of filtration, the wrong set-up can waste time and money!
I cringe when a contractor buys a simple inline 30-mesh filter for drip and spray systems because it's the inexpensive way to go. They don't want a 60-mesh filter because they'd have to clean it too often, but a clogged filter will be much easier to deal with than clogged nozzles and emitters!
A filter is clogged when there's a pressure drop of 8 percent or more as the water passes through the filter. One good way to avoid clogged filters is to install two 60-mesh filters parallel to one another, so that when one starts to get clogged, the water will follow the path of least resistance and flow through the secondary filter.
Another option is to have a filter with a built-in spinning action so larger debris settles to the bottom of the canister instead of sticking to the filter itself. Some periodic manual flushing of the filter will still be required to clean out the accumulated debris and the filter.
One of the best, though pricier, options is to have a filter with a built-in automatic cleaning mechanism that will scrub the filter when it hits that 8 percent pressure drop. At a lower cost, manual versions that require periodic cleaning by cranking or spinning a handle are also available.
Dealing with Organic Debris and Sand
If you have a lot of organic material in your irrigation water, it would be better to install disc-style filters, since a disc can handle three times as much organic debris before it’s clogged. However, for most local applications, sediment is the main issue and stainless steel mesh filters perform three times better at handling sediment and silt than disc filters.
If you have issues with mostly large sediments like sand, then a sand separator would probably be your best option. Keep in mind that a separator won't be able to filter out the fine silt in the water, only sand and other particles that would settle in water within three minutes if put in a stationary container. A separator works great with a pump system since it requires a good, steady flow to work properly.
A separator works by creating friction loss, so you'd need to size your pump to overcome the 10-12 psi pressure loss that it will create. The size of the separator you will need is based mainly on how much flow you need; there's no advantage in over or under sizing it. There are many great options for high-end residential applications in the $300-500 range that would prolong the life of your irrigation system over a traditional filter.
The great thing about separators is that there are no moving parts to clean or break down. An automatic purge valve also can be easily installed to eliminate any routine maintenance. As a backup for drip irrigation systems, I'd recommend installing a screen filter to stop the small particles that a separator could miss.
Filtration Must-Haves
The key to good filtration is to size it adequately for your particular system, be it drip emitters, spray heads or rotors. Make sure to just filter out what would clog up your system, and don't worry about the rest. Over-filtration just results in unnecessary costs and more maintenance. As a general rule, I'd recommend a 60-70 mesh range for spray heads and 100-mesh filters after the valves for drip irrigation.
The extra money spent on a good quality filtration system will pay for itself down the road with reduced maintenance and fewer part replacements.
