RE: [compost_tea] filter sizes
Thanks, Tom Good description and a useful chart. Now what size will pass fungi yet retain silt? Don't think it works that way. Kinda like trying to hold cars but pass trucks in a filter??? Bob
Tom Jaszewski <tomj_at_lvcm.com> wrote:
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_at_gardener.com]
Sent: Friday, December 20, 2002 12:17 PM
To: compost_tea_at_yahoogroups.com
Subject: Re: [compost_tea] mist blowers for CT
100 Microns sounds too small.....400 , I think, is the order....
Cheers,
Jeff
To unsubscribe from this group, send an email to:
compost_tea-unsubscribe_at_yahoogroups.com
Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
To unsubscribe from this group, send an email to:
compost_tea-unsubscribe_at_yahoogroups.com
Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
.
Received on Sat Dec 21 2002 - 11:02:26 EST
This archive was generated by hypermail 2.3.0
: Tue Feb 07 2012 - 14:26:35 EST