Absolute vs. Nominal

[dtai]

Hi,
I would like to know how we can convert a fluid filter absolute micron rating to nominal micron rating. If there is a way.

Thanks.

dtai

 

[amorrison]

See

http://www.filtercouncil.org/techdata/tsbs/89-5R.html

http://www.fsifilters.com/filtration_abs.nom.asp

http://doultonusa.com/HTML pages/absolute_vs_nominal_microns_rating.htm

http://www.tpub.com/content/engine/14105/css/14105_149.htm

All from a Google search – thanks Google !

 

[aspearin1]

Unfortunately, the answer is that you can't. I work for a filtration company which chooses to call filters that are 99.9% efficient "absolute"... and call anything else they want "nominal". If a company's marketing literature has a large gap between 100 and 1 micron and they need a 50 micron, then they may choose a filter with a spec range the same as 100, and market it as a 50 micron nominal. Typically, I find that our nominal filters are about 25% efficient at the rated particle size. What's worse is that different companies use different definitions.

The formal definition my company uses is: absolute- an arbitrary term used to describe or define a degree fo filtration...
nominal- (see absolute)

The point of it is, those terms are marketing terms. If you talk to a sales rep, look past the terms and ask about initial efficiency or beta ratio. Incidentally, beta ratio is a strange term equating efficiency to an absolute number the following are true: Beta ratio 100 = 99%; 1000 = 99.9%; 10,000 = 99.99%. Beta 1000 is in reality the best one could market. There are some which market beta 10,000, but they have not been found to live up to the hype.

ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee

 

[tomwalz]

The way we use the terms is to mean that the rating tells you what the largest particle allowed to pass though is within a certain %.

A 50 micron rated absolute will trap almost all 50 micron particles and larger. A 50 micron nominal will trap most 50 micron particles.

However, with the units we build, filter life is a major consideration. Our market is filtering machining and grinding coolants; water, oil and so on.

A one micron filter will trap 99% of all 1 micron particles and last less than an hour before it is clogged. A 25 micron filter can also trap 99% of all 1 micron particles and larger and last weeks or months.

What we do with our filter units is to take them into a customer's operation and run them. We collect the output and have it analyzed for particle size and count. Then we match this with filter life until we hit a combination the customer likes.

We supply a unit with a 25 micron nominal bag and 25 micron string wound filter following that removes over 99% of all particulate down to one micron.

Filter material and even supplier can make a huge difference in results. Supposedly identical filters from two different suppliers can give filter life of a few hours for one and a few weeks for the other while providing equivalent filtering by our testing.

Filters are cheap and the testing isn’t all that expensive.

Also, you might subscribe to cutting tool engineering. They do a lot on coolant management.

tom

 

[aspearin1]

Tomwalz touched on a good point. The filters are rated using contaminants and process conditions which are very unlikely to be similar to your own. You will find your best filters for your process by having a tech rep do some testing in your system.

Also, as Tomwalz pointed out, there is quite a bit of variation between filters of the same make, just like any other manufactured product. Handling, shelf-life, process variations, and variations in raw material all play a role in this. If consistency a primary concern, I would consider avoiding string wound cartridges and go with a depth resin bonded cartridge.

ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee

 

[tomwalz]

Dear Aspearin1

Thanks for the nice comments.

Tom

 

[dtai]

Thanks Gentlemen.

 

[mathndnumbers]

The question is "how to convert a fluid filter absolute micron rating to nominal micron rating."
just make more big holes and it can be rated "nominal". It's like "average".
Nominal means it can be hole for elephant and flea- but "average hole" is nominal.
Absolute means no bigger holes than stated. Correct me if I'm wrong.
Tess

 

[aspearin1]

"Hole size" is generally not quantifiable. It's the size of the particulate retained and at what efficiency. Each manufacturer has a different efficiency they consider "absolute." Each maintains the right to choose when during the life of the filter to call it "absolute." Some use the initial efficiency. Some use average efficiency over the life of the filter. Some may use final efficiency (which is very misleading), after the filter has already packed.

ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee

 

[zeusfaber]

"Nominal" is one of those dangerous words that seems to mean different things depending on where you learnt to speak English.

Here in the UK, we say "The fuel consumption is nominally this, that or the other", and we mean that "that is the figure I found in the book - but don't necessarily rely on it because I haven't checked yet".

In other parts of the world (certainly in the US), the same expression means "Having measured the fuel consumption, I'm pleased to say that it came in right on spec at....."

Not normally a problem, until the day it comes to bite you.

A.