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Types Of Sediment Filters

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All sediment filters have one thing in common, filtration capability based on micron (µm) size. By definition, a micron is "a metric unit of length equal to one millionth of a meter" which is extremely small to the naked eye. The diameter of a human hair is roughly 25 microns. If a filter is rated to be 5 micron nominal then it means that 80% of pores on that filter are 5 micron and the rest could be larger. If a filter is rated to be 5 micron absolute then 99.9% of the pores are 5 micron and the rest could be larger. All sediment filters lower the water pressure of a given water source. Sediment filters require very little water pressure to operate – about 5 psi.
Spun "Melt blown" Sediment Filters
These types of filters are most economical and are most widely seen on the market. They are noticeable for their hard cotton-like appearance. Typically, these are made of 3-4 different layers and are usually made to have the largest micron on the outer most layers to the smallest micron on the inner most layers. The rating of the filter is based on the smallest micron and most inner layer of that filter. Spun sediment filters are ALWAYS made of polypropylene. Polypropylene is a type of thermoplastic that can be melted and bonded which is how the term "melt blown" came about.
Spun "melt blown" filters are typically described to look like a clean white paint roller. Although they are sometimes slightly pleated (circling the sediment filter). These types of imitated "pleated" filters increase the surface area for water to filter contact which ultimately decreases the amount of water pressure drop (which is good). You will never see rubber gaskets on a sediment filter. Rubber gaskets are used to help separate the product water and the source "feed" water and is seen on EVERY other filter except spun filters. Sediment filters are self sealing when properly used.
Their dirt holding capacity is considered to be better than pleated but worse than string wound filters. Their main purpose is to remove silt, oil, grease, and other forms of sand. It is very commonly used as a general filter to remove more than the above mentioned (i.e. dirt, particulate rust/iron, etc).
The micron rating of a spun filter is ALWAYS rated as nominal and NEVER absolute. You will never see a spun filter with an absolute micron rating because of the way it is made.
Spun filters are an all around average filter which can be used in almost any situation.

String Wound Sediment Filters
String wound filters have the appearance of a spool with yarn. They have a lot in common with spun "melt blown" sediment filters. They both have ONLY a nominal filtration and are ALWAYS made of polypropylene. Much like spun filters these also do not use rubber gaskets to seal the filter.
For dirt, silt and sand situations, it is always recommended to use a string wound sediment filter. These have the largest of the pressure drops as well as the largest of dirt holding capacity. It is very common for people with well water to use these types of filters due to the fact that they have large amounts of dirt/sand/silt in their well.
It is not recommended to use string wound filters for water with high amounts of oils and grease. Because oils attach to the surface of the filter, it will deliberately clog the filter. This will increase the pressure drop until it is completely clogged.

Pleated Sediment Filters
Pleated filters are recognized for their paper thin appearance. Their appearance resembles a well folded piece of paper that is in the shape of a circle. These types only have 1 layer of filtration. It can be made of several types of materials that include cellulose, polypropylene, and polyester – each with its own advantages and disadvantages. They require the use of rubber gaskets to seal properly.Pleated filters have the least amount of pressure drop due to the thickness and most of the time can be washed and reused several times before it is tossed away. The surface area of a pleated filter is much larger than any non-pleated filter.
Polyester pleated filters are used for removing suspended solids from water and are the most durable of the pleated filters because of their material. They are the most resistant to bacterial growth. Polyester filters are constructed of pleated non-woven polyester fabric that is bonded on the ends to thermoset plastisol or "end caps." Polyester is resistant to many chemicals and to bacterial damage, making them an excellent choice for removing suspended solids from non-chlorinated water supplies such as lake and well water.
Polypropylene pleated filters are the most economical filters. They have a higher dirt capacity than polyester filters. Polypropylene construction is excellent chemical compatibility. It is a very good general filter like polyester.
Cellulose pleated filters are also used for removing suspended solids from water. Pleated cellulose is bonded to the end caps of the thermoset plastisol. Cellulose pleated sediment filter are designed for use on chlorinated water supplies such as lakes & rivers.
Both absolute and nominal filters are available because of the way these are made. Absolute micron filters are priced higher than nominal filters because of the production cost. For general filtration, nominal microns are more economical than absolute. Absolute is used in more strenuous situations, for example in laboratories, where micron size plays a very important function.
The main purpose for these types of filters is to remove more solidified particulates like grit, sand, particulate rust and other larger sediment particles. Pleated filters have the least dirt holding capacity when compared to spun and string wound filters. Although they may be used for dirt filtration, they may not perform well for dirt holding capacity.
Pleated filters are recommended for homes that cannot afford the pressure drop but have the presence of sand, grit, or sediment particulates.

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Our duty is to provide excellent water quality information to health conscious and home improvement do-it-yourselfers. Isopure Water - a WQA member since 2005 and continues to strive for improving water quality.