SpectraPure
03/19/2004, 11:08 AM
Much as “specs-manship†has permeated many industries, i.e., audio equipment, automobiles, microwave ovens, etc., so is the filter business rife with confusing information about “micronsâ€.
Filters are primarily rated as either ABSOLUTE or NOMINAL. Absolute means just that, ABSOLUTE. The most stringent way of grading filters. The way the laboratory boys do it.
Lo and behold, someone came along and started using the term, NOMINAL. Nominal is much harder to define and there is a huge disparity in how NOMINAL gets defined. For example, most filters that claim to be 10u (micron) NOMINAL (which could be 40u or more ABSOLUTE) are about as effective as chicken wire!
Here are three excellent references:
http://www.wcp.net/PDF/1102thusoo.pdf
http://members.aol.com/rgooz/sdi89.html
http://members.aol.com/rgooz/sdi1990ab.html
Some of this information is close to 15 years old, and is still irrefutable.
You will find that “Silt Density Index†(SDI) is best used to evaluate the suitability of water for RO. Our 0.5u NOMINAL Sediment Filter is really closer to 10u ABSOLUTE. It has an SDI less than 5.0. It is closest to the Type III filter in the second reference.
Most Carbon Block Filters are close to an ABSOLUTE rating.
Our 0.5u NOMINAL Carbon Filter is very close to 1u ABSOLUTE.
So, our 0.5 NOMINAL (10u ABSOLUTE) Sediment Filter is adequate to precede and protect our 0.5u NOMINAL (1u ABSOLUTE) Carbon Filter.
Why? Because MOST particle distribution in water is greater than 10u.
Sediment Filters can cost us anywhere from $0.60 to $10.00. Obviously, we try to select components that have the best price/performance ratios.
Our experience shows that it is a fallacy to ask or expect a Carbon Filter to do the job of a Sediment Filter. Carbon Filters should not be used for sediment removal because Carbon Filters need to be kept clean to be effective in removing chlorine. Dirty Carbon Filters have greatly reduced surface area needed for efficient chlorine removal.
IF we were to offer a Sediment – Carbon – Carbon array (and we are thinking about it), it would be: 0.5u Sediment – 1u Carbon – 0.5u Carbon. The clean 1u Carbon would take out the chlorine, leaving the 0.5u Carbon to work on residual chlorine as well as Volatile Organic Chemicals such as chloroform, benzene, trihalomethanes (THM’s), MBTE, etc. These and other “small molecular weight molecules†are the most likely to find their way through a membrane if not removed by the 0.5u Carbon Filter.
Here’s a simple test anyone can do:
Use “your†sediment filter ahead of “your†carbon filter. Let the filter array plug up and drop your membrane pressure (or production rate). Remove the sediment filter and see if the pressure (or prod. rate) goes back up. If it does not, it means the carbon has been plugged with dirt and the sediment is not doing its job.
Scott
SpectraPure, Inc.
Filters are primarily rated as either ABSOLUTE or NOMINAL. Absolute means just that, ABSOLUTE. The most stringent way of grading filters. The way the laboratory boys do it.
Lo and behold, someone came along and started using the term, NOMINAL. Nominal is much harder to define and there is a huge disparity in how NOMINAL gets defined. For example, most filters that claim to be 10u (micron) NOMINAL (which could be 40u or more ABSOLUTE) are about as effective as chicken wire!
Here are three excellent references:
http://www.wcp.net/PDF/1102thusoo.pdf
http://members.aol.com/rgooz/sdi89.html
http://members.aol.com/rgooz/sdi1990ab.html
Some of this information is close to 15 years old, and is still irrefutable.
You will find that “Silt Density Index†(SDI) is best used to evaluate the suitability of water for RO. Our 0.5u NOMINAL Sediment Filter is really closer to 10u ABSOLUTE. It has an SDI less than 5.0. It is closest to the Type III filter in the second reference.
Most Carbon Block Filters are close to an ABSOLUTE rating.
Our 0.5u NOMINAL Carbon Filter is very close to 1u ABSOLUTE.
So, our 0.5 NOMINAL (10u ABSOLUTE) Sediment Filter is adequate to precede and protect our 0.5u NOMINAL (1u ABSOLUTE) Carbon Filter.
Why? Because MOST particle distribution in water is greater than 10u.
Sediment Filters can cost us anywhere from $0.60 to $10.00. Obviously, we try to select components that have the best price/performance ratios.
Our experience shows that it is a fallacy to ask or expect a Carbon Filter to do the job of a Sediment Filter. Carbon Filters should not be used for sediment removal because Carbon Filters need to be kept clean to be effective in removing chlorine. Dirty Carbon Filters have greatly reduced surface area needed for efficient chlorine removal.
IF we were to offer a Sediment – Carbon – Carbon array (and we are thinking about it), it would be: 0.5u Sediment – 1u Carbon – 0.5u Carbon. The clean 1u Carbon would take out the chlorine, leaving the 0.5u Carbon to work on residual chlorine as well as Volatile Organic Chemicals such as chloroform, benzene, trihalomethanes (THM’s), MBTE, etc. These and other “small molecular weight molecules†are the most likely to find their way through a membrane if not removed by the 0.5u Carbon Filter.
Here’s a simple test anyone can do:
Use “your†sediment filter ahead of “your†carbon filter. Let the filter array plug up and drop your membrane pressure (or production rate). Remove the sediment filter and see if the pressure (or prod. rate) goes back up. If it does not, it means the carbon has been plugged with dirt and the sediment is not doing its job.
Scott
SpectraPure, Inc.