This report details the findings of a gravimetric analysis of a CC Jensen filter sample supplied by Harvey Klassen of Klassen Specialty Hydraulics Inc.  As per the original scope of work for this project, this report outlines the amount of material trapped in a representative sample of the filter.  In addition, based on an ICP analysis of the filter residue, further speculation is made as to the nature of the material trapped by the filter and possible route causes of the problem.  However, without further detailed study of the mechanical system as a whole, and further comprehensive testing of the oil and the filter, a definitive root cause cannot be determined, although some inferences can be made.

Filter – Visual Inspection and ICP analysis.

A cursory visual inspection of the filter indicates that the contaminants trapped by the filter are organic in nature, indicating that this material is likely due to by-products of lubricant degradation.  Furthermore, by looking at the cross sectional area of the filter, it is clear that the contamination is evenly dispersed throughout the full depth of the filter medium indicating that the contaminants are every small and able to penetrate into the center of the medium.

In order to gain some understanding of the type of material trapped by the filter, the filter residue was dissolved in kerosene and an ICP-AES measurement made.  24 elements were measured ranging from wear metals to common contaminants and oil additive elements.  Those elements that showed significant concentrations in the ICP analysis are given below:

The absence of significant concentrations of wear metals (e.g. iron) and contaminants (e.g. silicon) compared to the amount of residue in the filter (see below) indicates that the material trapped in the filter is likely a direct result of lubrication degradation.  The presence of oil additive elements (Ca, Zn and P) is not uncommon in this type of situation.  It is highly unlikely that these elements are found in the filter as a direct result of filtration, since additives typically found in AW hydraulic fluids such as Nuto H are dissolved in the oil and will not be stripped directly by this type of filtration.  Their presence is likely as a direct result of breakdown of these additives due to whatever mechanism is causing oil degradation to occur (see below).  The concentrations found in the filter by ICP are not high enough to indicate that most of material is anything other than organic in nature.  Without further analysis, including XRF data, the exact molecular form of these additive by-products cannot be determined.

Filter Gravimetric Analysis

Gravimetric filter analysis was performed at Southwest Research Institute (SWRI).  The procedure involved a reflux distillation procedure using a soxhlet apparatus, in conjunction with hexane as the solvent.  Heptane was used to remove all oil soluble and insoluble material to be extracted from the filter sample.  A 150-mesh screen was used to prevent filter material entering the reaction vessel and being counted as filter residue material.  After the distillation process the hexane was removed by rotary evaporation and the amount of material left behind weighed in relation to the mass of filter sample originally used.

Filter sample at end of test (EOT)
Residue after heptane extraction

Two filter samples were, each constituting a pair of disk elements.  Each sample was broken-up and a small portion refluxed for 3 days to remove all material.  The mass of each filter sample before and after reflux was determined, together with the mass of material left behind after evaporation of the hexane.

Data from the test procedures was as follows:

Based on the gravimetric analysis study, it is clear that each element pair held approx. 16 g of filter residue per 16 g of filter media although it cannot be determined whether the filter is indeed saturated at the levels measured in this study.  Based on this analysis, it is estimated that filter can hold as a minimum its own weight in trapped contaminants and lubrication by-products.  Based on ICP data, it appears that in this instance, the overwhelming majority of the filter residue is organic material from breakdown of base oil molecules.

Root Cause Analysis

Based on the data available, it is our opinion that the filter has become plugged with the by-products of oil degradation.  Oil degradation typically occurs in one of two ways, either oxidative or thermal fauilure.  However, based on information supplied by Gerry Trodd, it is our understanding that no increase in acid number from oil samples taken from the reservoir was observed in this instance.  This factor is consistent with a thermal failure mechanism.

Thermal failure is typically caused by one of two mechanical issues; either contact of the oil with excessively hot machine surfaces, or by an effect called micro-dieseling.  Micro-dieseling is a common problem in hydraulic systems, and is usually as a result of excessive air entrainment.  As entrained air bubbles pass through a hydraulic pump, the increase in pressure results in an adiabatic compression causing the temperature to rise.  This increased temperature, which may reach several thousands °F results in complete degradation of the oil, causing oil darkening, sludge and varnish formation and additive mortality due to thermal reaction.  This is a particular problem with sulfurous additives such as ZDDP antiwear additives used in AW hydraulic fluids and may explain the high Zn and P levels found in the filter residue and the depletion of these additive elements in bulk oil samples.  The data obtained from this study are all consistent with thermal degradation as the oil failure mechanism.

Further confirmation may be obtained by running a differential FTIR scan of new vs. used oil.  Typically, under conditions of thermal failure, a significant increase in nitration by-products is observed at 1630 cm^-1.  This test should be considered to further evaluate thermal failure as a root cause.

Should thermal degradation due to air entrainment be determined as the root cause, it is strongly recommended that the source of the excessive air entrainment be investigated and corrected.  While ultra-fine filtration is an excellent solution to extending machine life, it should not be considered as a long-term solution to excessive sludge/varnish build-up and is simply removing the by-products of oil degradation, after the problem has occurred.

Common conditions that can lead to poor air detrainment of the oil include, excessive contamination with water and other impurities, poor system design such as plunging return lines, poor reservoir design and in-adequate oil residence time and suction line leaks.  It is strongly recommended that each of these factors be considered and reviewed rather than relying on oil filtration to remove degradation by-products.  The use of a diffuser on the return line, if not already in use, together with appropriate reservoir baffling and a wire mesh screen should be considered.