Agitated Pressure Nutsche Filter. This filter was developed to address safety concerns due to solvents evaporation, as filtration under vacuum or pressure can be carried out in a closed vessel. It consists of a dished vessel with a perforated plate. The vessel, when designed for vacuum or pressure service, is leak proof, and can be maintained at a desired temperature. An agitator keeps slurry contents fluidized until material is filtered through and helps to maintain a uniform cake. After washing and refiltering, the cake is discharged by lowering the agitator and rotating it in such a manner that all cake moves towards the discharge port.
Things to Consider: Filter area, Vessel volume, Cake height.
Bag Filters. A sediment filter that is frequently used for dust removal. They are surface filters that block particles on the filter’s surface. Air flow can be from outside to inside the filter or visa versa, depending on the application. Bag filters are usually not designed for replacement when clogged, but can be cleaned by mechanical shaking or by backwashing with compressed air.
Things to Consider: Size, Material, Micron rating, Solids contained in bag, High solids collection capacity, Low operating costs, Long operating cycles, Ring material, Specialty oil removal and colloidal suspended solids removal, Welded seam, Extended life option.
Cartridge Filters. A sediment filter. They can be surface filters that block particles on the filter’s surface, or depth-type filters that capture particles through the total thickness of the medium. Cartridge filters are normally designed to be disposable and must be replaced when clogged.
Things to Consider: Type of filtration required, Dirt-holding capacity, Size, Micron rating, Compatibility with chlorinated water, Filter media materials, End caps materials, Netting materials, Core materials, Backing materials, Gaskets material, Temperature rating, FDA-compliant materials, Lifetime in terms of gallons of water processed, Effectiveness in filtering cysts, Flow rate, Pressure drop.
Mechanical Filters. These devices filter liquids by introducing a porous mechanical barrier into the flow. The barrier permits passage of the processed fluid, while resisting the passage of specific contaminants. Common types are sieve filters, media filters, screen filters, disk filters, and cloth filters.
Things to Consider: Solution to be filtered, Degree of turbidity or sediment load of liquid, Allowable pressure drop, Micron rating, Backwashing requirements, Flow rate.
Membrane Filters. These filters are constructed in very thin layers from polymers and other advanced synthetic materials. Thicknesses range from 100 to 200 micro-meters. Most are manufactured with approximately 70 to 90% porosity. They are used in industry, science, and research for a variety of applications, such as: water recovery and recycling, fluid and water purification, water desalination, and capture and recovery of fluid-suspended products. They are available in standard and custom configurations.
Things to Consider: Application, Pore size, Color, Surface plain or gridded, Wettability, Sterilization method, Maximum operating temperature, Bacterial endotoxin concentration, Gravimetric extractables percentage, Flow rate.
Pressure Leaf Filters. These filters are similar to horizontal plate filters except that filter elements are mounted vertically. They are very well suited for handling flammable, toxic and corrosive materials and are designed for hazardous environments where high pressure and safe operation are required. Slurry is pumped under pressure into a vessel that is fitted with a stack of vertical leaves that serve as filter elements. Each leaf has a centrally located neck at its bottom which is inserted into a manifold that collects the filtrate.
Things to Consider: Solids contents or concentration, Pressure rating, Materials of construction, Leaf spacing, Flow rate.
Sand Filters. There are two types of sand filters: sand filters and sand separators. The sand filter uses relatively coarse sand and other granular media to remove particles and impurities. The sand separators use centrifugal force to separate particles out of the water. The separated material drops into a reservoir where it can be removed. They are not true filters, since no physical barrier separates out the particles, but they are often used upstream of a filter to remove the bulk of the contaminant, where the filter does the final cleaning.
Things to Consider: Sand filters: Filter media required for each layer, Filter tank wall thickness, Working pressure, Safety factor, Factory test pressure rating, Underdrain pipe material and construction, Ratio of slot area in filter to area of inlet pipe, Ratio of orifice area in top laterals to area of inlet pipe, Manway provisions, Gasket and sealing provisions, Flow rate, Backwash rate, Dimensions, Weight; Sand separators: Application,Nominal flow rate, Pressure drop versus flow rate, Inlet/Outlet connection, Volume of collection chamber, Construction material, Powder coating, Micron rating, Specific gravity rating, Installation sequence relative to other water treatment devices, Stainless steel option, Dimensions, Weight, Warranty.
Screen Filters. A type of filter that uses a rigid or flexible screen to separate sand or other fine particles out of water. These filters are not recommended for filtering organic matter since these organic contaminants can be extruded through the filter if pressure drop is considerable. Screen materials include stainless steel, polypropylene, and nylon. Similar devices with larger openings designed to keep out large objects are called strainers.
Things to Consider: Material composition or alloy selection, Abrasion resistance, Corrosion resistance, Maximum temperature, Mesh count, Open area, Wear life, Size, Edge condition
Strainer. A screen installed in the flow that allows water to pass, but not larger items, which fall to the bottom or are held in a basket for later removal. Strainers come is several different styles. A plate strainer, a perforated plate through which water flows, is the simplest. The plate may be corrugated to increase surface area. A basket strainer is shaped like a basket and usually installed in a vertical cylinder. This type of strainer, which captures debris in a basket, is easier to clean. It offers more straining surface area than a plate strainer, improving flow rates and decreasing pressure loss.
Things to Consider: Meshes per linear inch, Diameter of wire, Aperture size, Open area percentage, Surface area, Flow rate, Pressure drop.
