Liquid Filters

View A Video on Liquid Filters- A Quick Introduction

There are many different kinds of liquid filters. Chemical filters are used in instances where solute purification is needed; any equipment that is used to separate constituent materials in a flow of liquid can be referred to as a chemical filter. Strainers and cartridge filters are more commonly used when larger particles should be contained. These and bag filters are among the most popular types of filters and are used in a number of applications. Textile mills, cosmetics, food and chemical processing, refrigeration, automotive, petroleum and oil, paper and pulp, marine, electronic, photographic, printing, medical, waste treatment and pharmaceutical industries all can make use of these and other filter varieties. Biodiesel filters, gas filters, hydraulic filters and coolant filtration are all commonly employed to enable product recycling as well as better mechanical performance. Wet dry filters, though less applicable in many industrial environments, are also used because they offer the unique ability to act as both liquid and air filters, providing enhanced filtration capabilities. Industrial water filters are among the most common liquid filtration utilities. Necessary in virtually every manufacturing plant as well as commercial building, water filtration is essential not only to improved product quality and productivity, but also the health and safety of workers. Small scale reverse osmosis water filters are used in many residential settings as well, ensuring that everyone enjoys clean and clear drinking water.

While the overall purpose of filtration is by definition to remove particulates from a fluid process stream, there are three main goals of liquid filtration. Filters may be used to acquire the suspended materials, clarify the liquid or in many applications, both. To accommodate these differing needs, both cake and clarifying filters are widely available. A filter cake is the solid material removed from a fluid. A cake is formed when large quantities of solute or particulate build up on the intake surface of the filter media. It is easily removed, washed and even sorted. Valuable materials, such as oil or metallic dust, are commonly obtained through liquid filtration and easily recycled or reincorporated into the production process to reduce waste and cut costs. Cartridge and bag filters often provide cake buildup. Strainers and other types of filters, however, are used solely for purification purposes. Because only larger particles are captured, or suspensions with low percentages of solids are being processed, there is no visible buildup on the filter media. Cake filters may be used simply for clarification as well with the cake being disposed of during maintenance. It is important to consider the chemical composition of the solids and solutes present in a liquid sample in order to safely and properly handle or dispose of filter build up.

As with the final intention of liquid filtration, there are three main types of filtration products available. Though commonly all-inclusive, the word "filter" actually refers to the housing or holding mechanism of a filtration system. The chemical, mat or barrier that clarifies liquid is the filter media. Liquid filtering products are therefore available in three configurations. Bulk filter media is the material component alone and is commonly bought as replacement or refilling components. Multi-filament mesh, micro-fiber and spun materials are examples of the most popular media configurations. Purchased in larger quantities, these organic and synthetic materials are easily cut to size, shaped and otherwise suited to specific filters. The filters may likewise be purchased separately and are often made of durable materials such as steel, stainless steel, aluminum and thermoplastics. These include cartridges, holders and frames among other designs. These options are preferred for applications that require custom or replaceable components. The third and final product option, however, includes both filter media and filter housing. These come fully assembled for easy installation, use, maintenance and replacement, making them especially popular in domestic environments as well as those that entail frequent replacement or maintenance. Most pre-assembled units are fully disposable. Purchased partially or pre-assembled, all liquid filters operate under the same basic function. A liquid is passed through a semi-permeable or porous substance, the filter media, which allows the liquid molecules to pass through while inhibiting the passage of large particulates and chemicals.

Liquid filters are necessarily diverse as they must accommodate a wide range of industrial, commercial and domestic applications. These devices remove and separate solids, dusts, chemicals and even odors from a given liquid process stream. Application specific system configurations allow consumers to select what compounds will be filtered and to what degree. Micro-filtration systems stop everything larger than 0.1 µm, while ultra-filtration removes particulates as small as 0.001 µm. Particle size is not the only determining factor in filtering system selection. High-flow filtration systems are used for situations that have a high amount of particulate, water count or acid, while low-flow filtration systems are used for the opposite reasons. Bearing filtration systems are able to keep the filtered lubrication oil clean and, in effect, extend the life and effectiveness of the oil while maximizing its performance. Additionally, vacuum dehydration systems use vacuums to move liquid through the liquid filters at a high flow rate. Manufacturers and suppliers can provide helpful insight into the necessary liquid filtration for a specific use. In addition to flow, media material and particle size, consumers should consider the pressure drop, continuous versus batch operation, size, porosity, absorption, ply, stream composition and temperature, load capacity and the efficiency or accuracy of a given liquid filter.

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Types of Liquid Filters

• Bag filters are receptacles that liquid is passed through to remove impurities.
• Biodiesel filters are used to clean and clarify biodegradable and environmentally friendly fuel alternatives to petroleum diesel.
  
• Carbon filters are filters that contain carbon in their solid state. They use absorption to remove unwanted soluble substances from water and can be found in many applications, including personal water filters and purifiers.
  
• Cartridge filters have a receptacle that holds the filter media.
• Chemical filters are used to remove chemicals with a carbon filter.
• Coolant filtration is the process of removing suspended debris or other unwanted impurities from a process stream composed of chemical compounds designed to cool machine and engine components.
• Filter media is the material through which liquid is passed to remove all particles and impurities.
• Fuel filters are designed to filter sediments from fuel supplies because particulates are harmful to engines and can significantly decrease engine life.
  
• Gas filters remove excess or unwanted debris and solutes suspended in gasoline that would otherwise impede performance and harm valuable engine components.
• Hydraulic filters are liquid filtration devices designed especially to remove and eliminate contaminants and impurities from hydraulic fluids. More than 70% of all hydraulic systems failures are caused by fluid contamination.
  
• Industrial water filters remove impurities from water in industrial settings.
• Liquid filtration is the systematic removal of organic and synthetic impurities from a fluid process stream.
• Pleated (convoluted or corrugated) filter elements consist of a number of uniform folds and generally have a geometric shape, such as a cone, cylinder, plate or others.
  
• Reverse osmosis water filters use pressure to force water through thin, microporous films or sheets in order to trap or retain unwanted particulate impurities and dissolved solids.
  
• Strainers are used in filtration systems to remove large particles.
• T-type filters have both inlet and outlet ports situated at one end. The ports of their major axes are in a straight line with the axis of the filter element perpendicular to the line.
  
• Water filter systems are complete units that begin with a "dirty" water source and result in a purified end product. In the system, unpurified water is filtered and then acquired as a "clean" product.
  
• Wet dry filters have filter elements that are designed to filter particle matter from both air and water. They can be found in wet/dry vacuum cleaners and fish aquariums.

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Liquid Filters Terms

Absolute Filtration Rating (AFR) - The diameter of the largest spherical particle that is able to pass through a filter in certain testing conditions. The AFR indicates the biggest opening in any given filter element.

Absorption - A process by which a solid is employed in the removal of a soluble substance from water.

Beta Ratio - The number of similar-sized particles moving upstream through a filter in a ratio to the number of particles moving downstream.

Bridging - A condition in which particles fill and block the entire area between adjacent sections of a filter.

Bubble Point - The gas pressure at which a constant stream of gas bubbles is released from a wet filter element under specified testing conditions.

Bypass (Relief) Valve - A mechanism that ensures proper fluid flow when pre-selected flow levels are surpassed. The valve allows for part or all of the fluid to bypass the filter.

Channeling - The tendency of contaminating particles to pass through a low-density area of a poor filter around its seal points.

Clarification - The filtering of liquids that have only a small amount of solid particles.

Collapse Pressure - Maximum pressure a filter element can withstand without any permanent deformation(s).

Cycle Length/Filter Life - The amount of time that a filter is able to operate effectively before it needs to be cleaned or replaced.

Differential Pressure - Difference in pressure between any two positions of a component or system.

Effective Area - Area of the filter element that is exposed to fluid flow.

Efficiency - Ability of a filter element to remove a particular contaminant at a specified contaminant concentration. Efficiency is typically expressed as a percentage.

Element (Medium) - The porous material that performs the actual filtration process.

Housing - An enclosure that directs the fluid flow through the filter element.

Mean Filtration Rating - The average size of the pores of a given filter media.

Media Migration - The release into the flowing fluid of components that make up the filter media.

Pore - A small opening in a filter that allows fluid to pass.

Rated Flow - Optimal flow for which a certain filter is designed.

System Silting - Collection and settling of micro-sized particles inside a fluid system.

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