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RE: [compost_tea] mist blowers for CT



I find this micron and mesh issue confusing….I found this today….

 

Don’t confuse MESH with MICRON 

  • Contrary to the accepted norm; mesh size, by itself, means absolutely nothing!
  • Remove the concept of trying to equate an arbitrary number (mesh) to a fixed number (micron)
  • Stick with a micron retention in particle removal

What is mesh?

It refers to the number of openings in a lineal inch measured from the center of one wire to a point 1” distant. It has nothing to do with the size of the hole and this is where confusion reigns. Someone gives you a mesh size (and this happens all the time) and through some hocus–pocus, a size in microns is given. How it ever evolved is beyond me and has caused more problems than people realize.

A simple example:

A 40 mesh filter screen has 40 holes per lineal inch – so what? Depending on which manufacturers catalog you use, you can end up with, and I hate doing this as a comparison, a micron retention ranging from 307 microns to 435 microns. For some applications, the difference is minimal, but for most companies, it can mean rejection of product or contamination.

What determines the disparity when you convert to microns?

That’s a good question, and I will answer it as simply as I can. The reason is this: manufacturers use different wire diameters. Why? My guess is due to the structural integrity of the screen, and a need to please everyone (you know what happens when you try that!).

Using our 40-mesh example, a manufacturer will use a wire diameter of 0.013", which results in smaller holes per linear inch. This calculates to a width opening of 0.012". The same manufacturer will then use a 0.008" wire diameter, which produces bigger holes and corresponds to a width opening of 0.017". Remember, we still have 40 holes per linear inch but our micron size has changed from 307microns to 435 microns.

 What can a company do?

 Well, the first thing you need to do is think in terms of microns. I know, your thinking what is a micron? For those who are not sure or forgot, a micron is 0.000039". How is it applied? In an ideal world, a particle distribution count would be taken – this breaks down the size and quantity of suspended particles in a sample liquid. Unfortunately, most companies do not have the budget or time to do this (the cost can run anywhere from $300 to over a $1000). So the next best thing is to evaluate (guess) or contact a filter specialist.  To help, use the mesh /micron chart provided – the most common are listed. It isn’t complete by any means, but it will get you pointed in the right direction.

 As a general rule of thumb, anything below 40 microns cannot be seen with the eye. Keep in mind that a mesh screen you're presently using, may not correspond to our chart. If this occurs, you will need to look at the nearest mesh/micron size and evaluate which is better (above or below). Better yet, determine which micron size is needed for particle removal.

 

 

Conversion Chart

 

Mesh

Nominal Particle Retention

Micron Rating

10

.065"

1666

20

.035"

897

30

.023"

590

40

.015"

384

50

.011"

282

60

.009"

230

70

.008"

205

80

.007"

180

90

.0051"

130

100

.0055"

141

150

.0046"

118

200

.0033"

84

250

.0024"

60

400

.0018"

45

700

.0012"

30

 

 

 

     

 

 

Tom Jaszewski

www.livesoil.com

702-595-7012

 

-----Original Message-----
From: Jeff Lowenfels [mailto:jeff@gardener.com]
Sent: Friday, December 20, 2002 12:17 PM
To: compost_tea@yahoogroups.com
Subject: Re: [compost_tea] mist blowers for CT

 

100 Microns sounds too small.....400 , I think, is the order....

Cheers,

Jeff



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