Water Filters Information
Water filters accept liquids of poor or unknown purity and discharge a clear, clean output.
Water filters remove impurities through finely porous physical barriers and/or chemical and biological processes. Presented in the context of the food industry, this lecture illustrates.
Video credit: Layne Christensen Company
- Granular water filters use sand, anthracite, garnet, or other media to remove impurities down to about 1 micron in size. Activated carbon (adsorption) and ion exchange (softening and deionization) techniques address chemicals/gases and dissolved inorganics respectively.
- Membrane filters capture smaller than 1 micron particles through microfiltration, ultrafiltration, and nanofiltration. Reverse osmosis filters are slow, but can be 90-99% effective. Three general types of membranes are,
- Depth which use absorption or entrapment
- Screens use a set pore size to sort particulates
- Surface membranes are made from multiple layers of media. When fluid passes through the filter, particles larger than the spaces within the filter matrix are retained.
- Distillation and ultraviolet radiation are filtration forms particularly effective against organics. Magnetic filters remove ferrous particles.
Gravity or pressure is used to push the water through the system.
- The filtration grade (micron rating) indicates smallest particle size separated (e.g., 5, 75, 300, 600 µm).
- Maximum liquid flow ranges (e.g., 0.5 to 150 GPM).
- Filters operate at a maximum pressure (e.g., 60 to 300 psi).
- Maximum temperatures are set (e.g., 175 to 268 F).
- Duplex transfer valves permit continuous filtration during change-outs.
- Integral bypass valves keep water flowing if the filter gets clogged.
- Spin-on (canister) filters prohibit a system from running without an element in place.
- High delta P indication notifies when the element needs to be replaced.
- Filters and their elements can be portable, reusable/cleanable and/or FDA compliant.
- Tank-mounted filters are attached to reservoirs. In-line filters interrupt a pipeline or hose.
Water filters are used in residences, municipality treatment plants, and industries such as electronics, biopharmaceutical, food and beverage, medical, pool and spa, and power generation.