Most fine filtration is measured in microns

Micrometer (micron) is a metric unit of measurement denoting one millionth of a meter. To give you some idea of how fine a micron is, consider that the smallest particle visible to the unaided human eye is about forty microns (you can see smaller particles through light diffraction).

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There are a few rules to remember when sizing a filtration system:

  • With in-depth cartridge filters, the slower the flow, the more efficient the cartridge is and the longer the user can go between change-outs. At Filters.com, we typically size housings to start out with a clean differential pressure of two pounds or less. You will find that many people in the filter business will quote housings that are undersized for an application so that they quote the lowest capital equipment cost.

 

  • The differential pressure (pressure drop) across both the cartridge and housing must be considered cumulatively. The pressure drop across the housing differs from housing to housing, but in most cases, it can be obtained from the housing manufacturer.

 

  • Assuming a cartridge vessel is designed for cartridges with a one-inch inside diameter, keep in mind that the flow through the bottom of each filter should not exceed 15-25 gallons per minute (for membrane pre-filters, try not to exceed 15 gpm). These flow rates should not be exceeded because turbulent flow is created on the interior core of the filter, which frequently cause unloading of contaminant from the filter media.

 

  • Always consider the viscosity of the material to be filtered when sizing filters or vessels. Also keep in mind that the viscosity of most materials varies depending on temperature. If you have an application where the customer does not want to go over a certain differential pressure and the temperature of the product can go through a wide swing, be careful to find out what the viscosity of the liquid is at both extremes of temperature.

 

Copyright 2008 Barney Corporation, Inc… www.Filters.com… Info@Filters.com…1.614.274.9069

 

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Particles to be filtered usually fall into one of two categories:

 

 

1.Non-deformable particles that under normal conditions (temperatures) do not deform. In some instances, non-deformable particles can become deformable with a temperature or chemistry change—an example of this would is a particle of resin, which at ambient temperatures may be solid, but at elevated temperatures turns liquid.

2. Deformable particles (frequently called gels) that deform when put under pressure. The amount of pressure needed to deform gels varies depending on the specific gel/particle. With deformable particles, if enough pressure is applied, the gel will deform, push out through the filter, and frequently re-agglomerate on the downstream side of the filter. Sometimes, when the particle re-agglomerates, it is larger than could be seen on the upstream side due to coalescence that may have occurred in the filter. In some instances, deformable particles can become non-deformable due to changes in temperature, chemistry, or other conditions.

Copyright 2008 Barney Corporation, Inc… www.Filters.com… Info@Filters.com…1.614.274.9069

 

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 Staged filtration provides the lowest cost per liter filtered

In staged filtration, different micron ratings and types of filters are utilized to filter out progressively smaller particulate matter. Typically, this is done for cost savings with the aim of producing the lowest cost per liter filtered. An example of staging filtration is a chemical plant with a river as its water source. The first filtration step might be to use large iron bars to keep out trees (stage one). Next, a coarse wire cloth might be used to keep out fish (stage two). Stage three might be to direct the water flow through a centrifugal separator to remove sand, followed by (step four) a bag filter to remove fine sediment, etc. In this example, a case could be made that a bag filter could do the entire job. The question that needs to be asked, however, is “What makes the most sense from an economic standpoint?”
Copyright 2008 Barney Corporation, Inc… www.Filters.com… Info@Filters.com…1.614.274.9069

 

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