Page 20 - Parker - The Handbook of Hydraulic Filtration
P. 20
Filter Media Types and Ratings
Filtration Fact The Multipass Multipass Test
Test
Filter media ratings The filtration industry Contaminant
uses the ISO 4572
expressed as a Beta Ratio Downstream
“Multipass Test Flow Meter Sample
indicate a media’s particle Procedure” to evaluate
removal efficiency. filter element perfor-
mance. This procedure
P Gauge Test
is also recognized by Filter
Filtration Fact ANSI* and NFPA**.
During the Multipass Reservoir
Multipass test results are
Test, fluid is circulated Variable Speed Pump
very dependent on the through the circuit Upstream
Sample
under precisely con-
following variables:
trolled and monitored
• Flow rate
conditions. The differential pressure As an example of how a Beta Ratio is
• Terminal pressure across the test element is continuously derived from a Multipass Test. Assume
recorded, as a constant amount of con- that 50,000 particles, 10 micrometers
differential
taminant is injected upstream of the and larger, were counted upstream
• Contaminant type
element. On-line laser particle sensors (before) of the test filter and 10,000
determine the contaminant levels particles at that same size range were
upstream and downstream of the test counted downstream (after) of the test
element. This performance attribute filter. The corresponding Beta Ratio
(The Beta Ratio) is determined for would equal 5, as seen in the following
several particle sizes. example:
Three important element performance
characteristics are a result of the
Multipass Test:
1. Dirt holding capacity.
# of particles upstream
2. Pressure differential of the test B =
x
# of particles downstream
filter element.
3. Separation or filtration efficiency,
“x” is at a specific particle size
expressed as a “Beta Ratio”.
Beta Ratio
50,000
The Beta Ratio (also known as the B = = 5
10
filtration ratio) is a measure of the 10,000
particle capture efficiency of a filter
element. It is therefore a performance
rating.
* ANSI – American National Standards Institute
** NFPA – National Fluid Power Association
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