Hydraulic Oil Filtration Terms


-Filtration ratio,   βx   ( filtration efficiency )

This means the ratio between particles counted up stream and down stream, detected according to the multi – pass test method ( ISO 16889 ). For comprehensive evidence of the filtration range the ratio βx (c) is shown as a time related average value in the following rates

βx = 2                      βx = 10
βx = 75                   βx = 100
βx = 200                βx = 1000

Dirt – holding  capacity

Gravimeter determination of the mass particles in grams according to ISO 4572 is the mass which could be absorbed by the filter element until a point where one of the test limits ( time or pressure ) is reached.

Burst pressur.

According to ISO 2941 the burst pressure is the maximum allowed pressure when filter material still has complete operatability.

– Breaking strength.

The breaking strength of INTERNORMEN – filter elements is the maximum allowed pressure difference. However, high rate of security is given before the component are destroyed.

– Bubble – point test:
*Determination of the production quality according to ISO 2942
Function of the standard:
Examination or confirmation of the perfect production of filter element. The examination according to this standard is for:

– The release of further tests

– The release of an element after production (final control)
– The release for operational use ( Vendor inspection ).

-Maximum allowed pressure loss at the filter ( ∆p max )

During the normal volume flow in flow direction the maximum allowed pressure loss grows without negative impact of the filter function.

– Effective filtration area:

The total filtration surface of the porous material or of the wire mesh of the filter element which is penetrated by the flow rate.

– Filter efficiency:

Nominal filter efficiency:
Arbitrary statement of the filter fineness in micron, to be considered as a rough statement only.

Absolute filter efficiency:
Biggest diameter in micron through which particles could flow under specific test condition.

– Filter Service life
Is the operating time in practical operation until the contamination level of the filter is so high that the allowed flow resistance is exceeded.
– Contamination class

The transmission of the power hydraulic – and lubrication systems is effected through fluids under pressure.
These fluids have a natural contamination (primary and secondary contamination)
The level of this contamination (number of particles in a defined fluid volume) is defined in standards ISO 4406 and NAS 1638.They are divided into contamination classes.

Flow-fatigue test

The filter element is tested to ISO 3724 to examine the ability of the element to withstand alternating flows.

Flow-fatigue test

(A) Test filter

(B) Dirt addition (ACFTD) until the final pressure difference is reached.

A specified number of pressure shock cycles are sent to the filter element. The pressure characteristic must be sinusoidal and have a frequency of ≤ 1 Hz. The filter element has passed the test if there is no visible sign of damage on the complete element, seals or filter material after the pre-determined (or customer specified) number of pressure shock cycles have been endured.