Norgren Filter Contents - Manual (Page 7)

Rating Filter Elements and ISO Standard 8573-1
Littleton, CO USA Phone 303-794-2611 www.norgren.com ALE-Filter
Absence of an Industrial Standard for Rating
Pneumatic Filter Elements
There is not an industry wide standard for establishing the micron
rating of pneumatic filter elements. Standards by various industry
associations, including the National Fluid Power Association
(NFPA) and International Standard Organization (ISO), are in
discussion. In the absence of an industry standard, some
manufacturers of pneumatic filters make claims concerning the
micron rating of their so called “standard” element which can not
be substantiated and are probably not valid.
Norgren’s Method of Rating and Testing
Pneumatic Filter Elements
Norgren particle removal filter elements are rated by the size of
the particle they will trap (i.e., a 40-micron element will remove
particles 40-microns and larger). Norgren tests filter elements by
using standard coarse and fine test dusts of known particle size
distribution. Coarse dust consists of 12% particles smaller than
5-microns; fine grain dust consists of 39% particles smaller than
5-microns. Test results show that a Norgren filter element rated at
40-microns actually removes over 98% of particles 5-microns and
larger.
How to Size a Filter Element
The downstream equipment being protected determines the
micron rating of the filter element. Industrial tools, such as air
hammers and drills, typically require only a 40-micron element.
Air operated instruments and small, high speed tools typically
require a 5-micron element. Always consult the equipment
manufacturer for filtration requirements.
Generally, the smaller the micron rating of the element,
● the higher the pressure drop across the filter,
● the shorter the element service life.
Therefore, the use of a 5-micron element where a 40-micron is
adequate penalizes the customer in increased pressure losses
and frequent down time for changing or cleaning the filter element.
ISO Standard 8573-1. Compressed Air
for General Use
Contaminant’s found in industrial compressed
air systems include solid particles, water, and
oil. ISO 8573-1:1991 provides a simple method
of classifying these contaminant’s. A quality
class required for a particular application can
be defined by listing, in order, the class
required for solids, water, and oil.
Examples:
Air of Quality Class 2.2.2 is filtered to 1µm
solid particle size, dried to -40°F (-40°C)
pressure dewpoint, and filtered to an oil
concentration of 0.1mg/m
3 .
Air of Quality Class 5.3.4 is filtered to 40µm
solid particle size, dried to -4°F (-20°C)
pressure dewpoint, and filtered to an oil
concentration of 5mg/m
3 .
When a class for a particular contaminant
solid, water, or oil is not specified, the number
designating the class is replaced with a
hyphen.
Example: Air of Quality Class 1.–.1 does not
specify the pressure dewpoint.
Table 1. Summary of ISO 8573-1:1991 Air
Quality Classes *
Solid Water Oil
Particle Maximum Maximum
Maximum Pressure Remaining
Quality Size Dewpoint Oil Content
Class µm °F (°C) mg/m 3 ** (ppm)
1 0.1 -94 (-70) 0.01 (.0084)
2 1 -40 (-40) 0.1 (.084)
3 5 -4 (-20) 1 (.84)
4 15 38 (3) 5 (4.2)
5 40 45 (7) 25 (21)
6 — 50 (10) —
* See ISO standard 8573-1 for complete
information.
** At 1 bar absolute pressure.