How Sand Media Filters Work
Sand media filters are a proven method of purifying water and are preferred by many farmers due to their simple operation and large capacity. Designed to remove organic debris and particles from water, sand media filters extend the life of irrigation systems and prevent emitters from plugging. The filters are set up as a series of tanks filled with a certain type of sand. Contaminants are filtered out of the water as it flows through the media in the tank. The water is pressurized and forced through the top of the tanks, pushed through the sand media, and out of the tank into the irrigation lines.
The media is small and sharp-edged; the jagged edges fit closely together to trap particles more effectively than regular sand. The sharp edges also snag organic contaminants as water flows through the tight spaces. Specific media type and grain size and are not universal, but Streamline has found the best results with #16 silica sand and a base layer of 3/8” gravel. This size of sand provides filtration at around 180 mesh while the large gravel prevents the finer media from leaving the tanks. Sand media choice depends on water quality, filtration objectives, and length of filter runs.
Filtering and Flushing
Sand media filters are good at removing fine solids. Larger particles reduce the effectiveness of the filter because contaminants build on the top layer of the media, resulting in pressure loss. To get rid of filtered particles, sand media tanks regularly back-flush with filtered water. During this process, clean water from one tank is pumped backwards through another tank to remove the accumulated particles from the media. This is why it is necessary to have more than one tank in a filter station. The removed particles are drained through a flushing manifold away from the tanks. This preventative maintenance allows the filter media to be used continuously and quickly resume operation under normal pressure. If the water consistently carries more particles than sand media is able to remove, a separate filter such as a gravity screen may be needed before the tanks.
Benefits of Higher Filtration
These filter systems are considered vital for drip and sprinkler irrigation. Drip systems need good filtration because the drippers can quickly become plugged with sandy water. The ideal scenario is to use the highest level of filtration that is practical. Even if particles do not cause clogging in the system, removing them minimizes the wear caused by grains that would otherwise be pushed through.
Sand, rock, and other grit are not the only particles these filters remove. Organic materials like algae and slime also pose a threat to irrigation systems. In some cases, small fish or freshwater clams have plugged irrigation systems.
Timers, Gauges, and Switches
These filter stations come with a controller to schedule how often the system will backwash, how long, and the time in between each tank. The tubing that runs along the tanks allow the controller to read the pressure difference between the top inlet and bottom discharge manifold. As particles build up and reduce pressure, the differential increases until it triggers a switch that starts a flush cycle. This allows the filters to keep operating with a minimal drop in pressure. A pressure gauge on the outside of the tanks will indicate top and bottom pressures, it is usually located at eye level on the inlet manifold.
The technical parts of tanks might seem daunting at first, but once their operation is learned they require very little input. The main benefits of this system are its dependability, the simple way it removes contaminants, and that it can continue irrigating throughout its cleaning cycle. Most farmers agree that sand media tanks greatly improve their water cleanliness and are worth installing for the maintenance time they save.