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myv65 · 07-09-2003, 10:45 PM

Hey Ben,

You're into my present career area now. I have not bothered with your other thread, but am curious how you got to 570 microns. Is this some sort of minimum passage (awfully small for that) or something else? Quick summary would help as I'm too lazy to go looking through another thread. Where are the particles generated? Are they steadily being generated or do you need to do a one-time cleaning?

Anyway, you've got two very broad categories. There are absolute filters and nominal filters. Microscreens are an absolute filter as no particle larger than the pore size may pass. Larger particles may break up and pass, however. Nominal filters have no defined pore size but do get a size rating. Most paper elements are of this type. They'll remove most particles above the rating and many below the rating but allow progressively more to escape as size drops.

As a general rule, screens are pretty bad if you have a steady load of particles to remove. They offer no depth, hence can't really "store" solids. Head loss builds rapidly as solids accumulate. Paper elements and cloth elements each have a defined depth of filtration and offer higher solids storage between cleanings. Head loss does not develop as rapidly for a given solids load.

In each case, the accumulation of solids assists in the removal of new solids. The solids that build up form an additional barrier. The down side is what I've already mentioned: increased head loss.

The filters we manufacture are for water treatment. We use cloth media and design for a velocity through the media of ~15 m/hr. This limit is more due to using gravity feed and dealing with solids on the order of 10-50 mg/l. The media itself can handle pretty much any flux rate, but higher fluxes blow apart larger solids. The media carries a nominal rating of 10 micron and has a "clean cloth" loss on par of 1" H2O for every 10 gpm/ft^2. If you want a true flow of ~5 gpm and could tolerate losing six inches of head, you'd need 1/10 ft^2 or about a 4+" diameter cloth.

No, I haven't got anything that would suit your need. I work in the scale of MGDs, millions gallons/day. Although I do have a little lab-scale unit that cost ~$6K to build. It even uses one of those Little Giant pumps you're so fond of. . .

Either way you need a method of cleaning the filter. "Backwashing" or "backflushing" is most common and as the word suggests it involves reversing flow through the element. We control this automatically with a PLC, wash pump, valves, etc. Depending on how often you need to clean, you could incorporate this pretty easily into a system.

07-09-2003, 10:45 PM	#9
myv65 Cooling Savant Join Date: May 2002 Location: home Posts: 365	Hey Ben, You're into my present career area now. I have not bothered with your other thread, but am curious how you got to 570 microns. Is this some sort of minimum passage (awfully small for that) or something else? Quick summary would help as I'm too lazy to go looking through another thread. Where are the particles generated? Are they steadily being generated or do you need to do a one-time cleaning? Anyway, you've got two very broad categories. There are absolute filters and nominal filters. Microscreens are an absolute filter as no particle larger than the pore size may pass. Larger particles may break up and pass, however. Nominal filters have no defined pore size but do get a size rating. Most paper elements are of this type. They'll remove most particles above the rating and many below the rating but allow progressively more to escape as size drops. As a general rule, screens are pretty bad if you have a steady load of particles to remove. They offer no depth, hence can't really "store" solids. Head loss builds rapidly as solids accumulate. Paper elements and cloth elements each have a defined depth of filtration and offer higher solids storage between cleanings. Head loss does not develop as rapidly for a given solids load. In each case, the accumulation of solids assists in the removal of new solids. The solids that build up form an additional barrier. The down side is what I've already mentioned: increased head loss. The filters we manufacture are for water treatment. We use cloth media and design for a velocity through the media of ~15 m/hr. This limit is more due to using gravity feed and dealing with solids on the order of 10-50 mg/l. The media itself can handle pretty much any flux rate, but higher fluxes blow apart larger solids. The media carries a nominal rating of 10 micron and has a "clean cloth" loss on par of 1" H2O for every 10 gpm/ft^2. If you want a true flow of ~5 gpm and could tolerate losing six inches of head, you'd need 1/10 ft^2 or about a 4+" diameter cloth. No, I haven't got anything that would suit your need. I work in the scale of MGDs, millions gallons/day. Although I do have a little lab-scale unit that cost ~$6K to build. It even uses one of those Little Giant pumps you're so fond of. . . Either way you need a method of cleaning the filter. "Backwashing" or "backflushing" is most common and as the word suggests it involves reversing flow through the element. We control this automatically with a PLC, wash pump, valves, etc. Depending on how often you need to clean, you could incorporate this pretty easily into a system.