As the name suggests the Micron Cartridge Filters are filters which filter the water to designated Micron rating. This is achieved by specially designed cartridge elements to be housed inside the Filter vessel.
Micron Cartridge Filters Ratings
All cartridge filters have micron ratings that indicate the smallest sized particle they are capable of removing. One micron, symbolized by the Greek letter μ, is also known as a Milimicron, which is 1/1,000,000 meter. One micron = 0.000039 inch. Micron ratings for filter cartridges range from 50 microns (all filter cartridge types) down to 0.035 microns (Pleated membrane cartridges).
For RO (Reverse Osmosis) normally 10 µ, 5 µ and 1 µ cartridge elements are used.
Absolute vs. Nominal Filter Ratings
The micron size ratings can be “Nominal” or “Absolute.” A nominal rating indicates that the filter cartridge will remove 95% of the particles of that micron size. An absolute rating indicates that the filter will remove 99% of the particles.
Pressure Drop
The pressure drop across a cartridge filter is used to determine the condition and effectiveness of the cartridge.
A high pressure drop across a cartridge filter, over the maximum recommended pressure drop, indicates that the cartridge probably needs replacement.
No pressure drop at all indicates that the filter is either breached or that the seals are not working, and again needs attention. In most cases the attention needed is cartridge replacement. With some of the pleated filter cartridges, a cleaning can restore an acceptable pressure drop.
When to Replace a Filter Cartridge
As particles accumulate on a filter cartridge, flow through the filter becomes restricted. This restriction reduces the flow rate through the cartridge and increases backpressure. (It also increases the effectiveness of the filter, so cartridges shouldn’t be changed unnecessarily.) The difference in pressure before and after a cartridge filter is the pressure drop, or ΔP (Delta P).
Different filter configurations and micron ratings have different ΔP replacement specifications. For example, pleated membrane filters normally require replacement at a ΔP of 15 psig, while string filters are still going strong at a ΔP of 25 psig. Consult the manufacturers’ ΔP recommendations for the specific filter cartridge being used.
Filter Housings
Cartridge filter housings are available in different material of construction as required and to suit for the end user applications. Generally Carbon Steel and FRP housings are used for water treatment applications and stainless steel housings are preferred for high purity water treatment applications. Construction of these housings differ with respect to the operating pressures .
Filter Cartridge Types
Melt blown (Solid) Filter Cartridges
A melt blown filter cartridge is a “depth” type filter that is good for the removal of relatively uniform sized particles throughout the body of the filter, not just on the surface. Melt blown filter cartridges are particularly effective on well waters and normal city water.
The standard 10”, 5-micron, melt blown filter cartridge is the least expensive and most widely used filter cartridge on the market today. The melt blown 5-micron cartridge is used extensively for both commercial and domestic applications.
Typical applications include:
• 1 to 50 micron filters used in general purpose applications, with the 5-micron cartridge being the most popular.
• 5-micron filters installed up-stream of ion exchange resin columns to remove particles and down-stream to remove resin fines that could pass through under drains and clog a pure water system.
• 5-micron pre-filters installed ahead of a reverse osmosis system to remove particles that could clog up membranes and deteriorate performance.
String Wound Filter Cartridges
The string wound cartridge was the original cartridge filter element. A string wound cartridge is a “surface” type filter that is effective in removing diverse sized particles. It removes particles of its micron rating with excellent resistance to being “blinded” by larger particles. Because of the overlapping nature of the string windings, it has an effective surface area considerably larger than that of the melt blown filter. String wound filters are particularly applicable to surface waters from streams and rivers.
While string wound cartridges predate all the other filters, with polypropylene fibre construction, a string wound is still a good general-purpose filter and in certain applications, the best choice. Unlike the melt blown filter cartridge, string wound cartridges are inexpensive. In its 10”, 5-micron form it is the 2nd most commonly used filter cartridge on the market and is used extensively in pre-filtration applications.
Typical applications include:
• 1 to 50 micron filters used in general purpose applications.
• 5-micron filters installed up-stream of ion exchange resin columns to remove particles and down-stream to remove resin fines that could pass through under drains and clog a pure water system.
• 5-micron pre-filters installed ahead of a reverse osmosis system to remove non-uniform sized particles.
Pleated Filter Cartridges
A pleated cartridge is a “surface” type filter cartridge that is effective in removing diverse sized particles in limited quantities. Pleated cartridges will remove particles of its micron rating with good resistance to being “blinded” by larger particles. Pleated filter cartridges are particularly effective on surface waters from streams and rivers.
Pleated filter cartridges are constructed to provide a surface area far in excess of the diameter of the filter. The micron rating of a pleated filter is more precise than either the melt blown or string wound cartridges. Though pleated cartridges are more expensive than melt blown or string wound, they are the only choice for sub-micron filtration. (0.45 to 0.1 microns) Sub-micron pleated filter cartridges are used extensively as biological blocks in the production of high-purity and sterile water.
Typical applications include:
• 5-micron general-purpose filters used before and after ion exchange resin columns.
• 1 to 50 micron filter on the vent of a water storage tank to help prevent airborne particles from entering the tank during draw down in non-critical applications.
• 0.45 sub-micron post-filters installed after ion exchange systems act as final filters for particle sensitive applications.
• 0.2 sub-micron post-filters are installed after ion exchange and ultraviolet sterilization systems to act as final filters yielding bacterial and particle counts of near zero.
• 0.1 sub-micron hydrophobic filters are used extensively on the vents of a high-purity water storage tanks to prevent airborne dust and microorganisms from entering the tank during draw down in critical applications.
• 0.1 to 0.2 sub-micron “Absolute” filters for both system and point-of-use filtration in critical applications.
Media Filter Cartridges
A Media Filter cartridge is not like the mechanical filters described above. A media cartridge is actually a water treatment device that effects chemical changes in the water. The flow rate through a media cartridge is substantially lower than that a similarly sized particle filter. For example a 10” 5-micron filter can flow at 5 GPM, while the same sized Carbon Media cartridge flow rate may be even less than 2.5 GPM depending on chlorine and organic loading.
Replacement of media cartridges is not dictated by pressure drop. Carbon media cartridge replacement should be scheduled for every three months or more often. Deionizer (DI) cartridges should be replaced according to outlet water quality.
Typical applications include:
• Activated Carbon for the removal of chlorine, taste and odour.
• Mixed Bed DI resin for water purification.
• Calcite media for neutralization of acidic water.
Cartridge Filter Accessories
Accessories include: Filter housing wrenches, Inlet and outlet pressure gauges, isolation valves and pressure relief valves.