Kidney Filtration-Secondary Effects???

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Does kidney filtration improve or degrade viscosity improvers, additives, moly, TAN etc.? Most hydraulic fluids are shipped 20/17/15, or thereabouts. I always kidney filter for 12 hours in the factory container prior to the filtered transfer to the reservoir yielding improved filtration to 13/9/6, or thereabouts. In reviewing oil analysis, it has shown changes in PPM counts for additives and moly as well as TAN, is the viscosity index also affected by kidney filtration? Thank you
 
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In general it has no effect at all on any of them. In base stock pre-filtering and recirculation's ( usually with carts)- you may see variances in certain concentrations but that's a result of agitation relative to sampling location- not the filter set up. If recircing into the OEM container you will also often experience a remix of settled particles skewing all data- that's why the receiving container needs to be purged and cleaned to ISO cleanliness in the lube room prior to filling. Unless you have a true membrane set up, no conventional coalesce or particulate filter on any commercial kidney rig will have a significant effect on filtration of additives ( assuming they were mixed properly in the first place). If that's occurring then something else is most likely wrong or there's something uncontrolled skewing the results.
 
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MolaKule

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Originally Posted by TravlinTech
Does kidney filtration improve or degrade viscosity improvers, additives, moly, TAN etc.? Most hydraulic fluids are shipped 20/17/15, or thereabouts. I always kidney filter for 12 hours in the factory container prior to the filtered transfer to the reservoir yielding improved filtration to 13/9/6, or thereabouts. In reviewing oil analysis, it has shown changes in PPM counts for additives and moly as well as TAN, is the viscosity index also affected by kidney filtration? Thank you
Unless your kidney loop filtering system can filter out 0.01 micron particles i'd say there should be no change in elemental or chemical analysis. 0.01 micron = 10 nanometers and 10 nanometers is the average size of oil molecules, and even high molecular weight VII's may only reach 100 nanometers.
 
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Thank you for the replies. Would it be accurate to say that the additives are not fully soluble? Or that the additive may be approaching, or has approached a saturated concentration? For example the 275 gallon tote was sampled after 8 hours of filtration- after 12 hours of filtration (last 3 in reservoir) and after 13 hours of production use. by a Parker cart with 40 & 10 filters. TAN was 1.84-1.69-1.75, Moly was 301-338-354, Phosphorous was 718-751-857 and Zinc was 634-676-715. The three cleanliness levels were 17/15/9, 15/11/6 and 15/11/7. The equipment has a 6 micron glass filter. ISO 46, oxidation stability is >5000, VI was 168. Thank you for your input.
 

MolaKule

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Originally Posted by TravlinTech
Would it be accurate to say that the additives are not fully soluble? Or that the additive may be approaching, or has approached a saturated concentration?
No. Are we discussing virgin finished lubricants or are we discussing used hydraulic oils being filtered for reuse - or both? Finished virgin lubricants do not contain additives in saturated concentrations. The main additive package, called the Di package contains the proper mix of chemistry necessary to do the job over the life of the lubricant. The additives are blended with the base oils and VII at about 100F. Solubility of the additives in the finished lubricant depends on the base oil type and other additive chemistry present. For example, if an ester-based dispersant is used there is usually no reason to add other esters or additional solving chemicals to keep the additives dispersed or in solution. The only additive that can possibly precipitate out over time is the detergent which contains a reacted mixture of alkylarylsulfonic acids with calcium or magnesium, or sodium metals with carbonates, but that can be mitigated by heating and stirring. However, the carbonate molecule itself is submicron in size as well. What people usually see or describe as additive "fallout" is simply an agglomeration of the mostly detergent components separating out. But them again, heating and agitation fixes this. Loop filtering of used hydraulic oils make sense since they can pick up dirt particles in operation but filtering virgin finished oils from totes makes little sense to me unless there is something I am missing as to your ultimate goal(s).
 
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Virgin finished hydraulic fluid. The ISO cleanliness from the OEM is unsatisfactory for the application due to a frequent function that requires minimum bypass at the spool of a directional valve when holding a cylinder in neutral when the cylinder has very high pressure on the rod end. Low VI is a secondary issue when fluid temperature is elevated due to environmental conditions and/or high cycle times. Add OEM TD sheets that state given specifications but produce far from it, collectively, this makes it a challenge in delivering properly functioning equipment to end users. Thank you
 

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This is new to me. When we change hydraulic fluid in large/expensive systems (with many end users) … the OEM wants us to filter that entire system with a portable skid before going on just the HPU filters … but in all my years never required factory filled containers to be filtered.
 

MolaKule

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Originally Posted by TravlinTech
Virgin finished hydraulic fluid. The ISO cleanliness from the OEM is unsatisfactory for the application due to a frequent function that requires minimum bypass at the spool of a directional valve when holding a cylinder in neutral when the cylinder has very high pressure on the rod end. Add OEM TD sheets that state given specifications but produce far from it, collectively, this makes it a challenge in delivering properly functioning equipment to end users. Thank you
Have you discussed this particulate situation with the OEM and have you measured pressures at various points in the system to make sure you are attacking the real problem? Why haven't you located an OEM that can meet your minimum particulate specifications?
Originally Posted by TravlinTech
Low VI is a secondary issue when fluid temperature is elevated due to environmental conditions and/or high cycle times.
Then find a quality fluid that has a better Viscosity Index. I don't know what the last part of your sentence is supposed to convey. What environmental conditions affect virgin hydraulic fluid? What kind of hydraulic equipment/application is this that needs such a low particulate count? I have never seen a hydraulic system that couldn't tolerate 6-10 micron particles.
 
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Originally Posted by TravlinTech
Virgin finished hydraulic fluid. The ISO cleanliness from the OEM is unsatisfactory for the application due to a frequent function that requires minimum bypass at the spool of a directional valve when holding a cylinder in neutral when the cylinder has very high pressure on the rod end.
How exactly was this determined and by whom? If it only happens in a load state ( based on your description) then its much more likely you have components or fluid possibly not rated ( or de-rated) for that specific load. What direct causal link between fluid cleanliness to ISO and valve function did you draw and how did you verify it?
Originally Posted by TravlinTech
Low VI is a secondary issue when fluid temperature is elevated due to environmental conditions and/or high cycle times.
Issue defined in terms of what malfunction? Again, this sounds like a de-rating issue due to improperly spec'd parts/fluid or running out of design range based on your information provided.
Originally Posted by TravlinTech
Add OEM TD sheets that state given specifications but produce far from it, collectively, this makes it a challenge in delivering properly functioning equipment to end users.
That doesn't really say much but assuming this is a new application and this is in commissioning, this performance is in the "infant mortality" portion of the bath tub curve and the OEM should have people there addressing it. If this is something custom designed, re-purposed or "Frankensteined" then those who developed it need to start doing a design review or review the desired outputs against the BOM for components selected. Hydraulic systems are reasonably simple and extremely robust when designed and operated properly- the conditions you are describing do not suggest or primarily point to a fluid contamination problem in any way.
 
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Originally Posted by MolaKule
Originally Posted by TravlinTech
Virgin finished hydraulic fluid. The ISO cleanliness from the OEM is unsatisfactory for the application due to a frequent function that requires minimum bypass at the spool of a directional valve when holding a cylinder in neutral when the cylinder has very high pressure on the rod end. Add OEM TD sheets that state given specifications but produce far from it, collectively, this makes it a challenge in delivering properly functioning equipment to end users. Thank you
Have you discussed this particulate situation with the OEM and have you measured pressures at various points in the system to make sure you are attacking the real problem? Yes, they required education on the subject, as well as education on oxidation and varnish, since they did not know the root cause. The OEM utilizes my services for advanced product defect resolution, I go to where their in-house staff fails to satisfy the end-user. They also had no familiarity with vibration monitoring and utilization of those measurements, this is a completely different issue that is not fluid related. Gauges on various ports of the manifold prove the bypass at the spool. Why haven't you located an OEM that can meet your requirements? The fluids I have evaluated have all fallen short of their TD specifications. In fact, the fluid removed after 7500 hours, was cleaner in the 4 micron range than the new fluid in the drum. 20/18/13 vs 22/18/12. Then find a quality fluid that has a better Viscosity Index. I don't know what the last part of your sentence is supposed to convey. What environmental conditions affect virgin hydraulic fluid? I have been testing/evaluating various fluids for several years, unfortunately many fluids TD's oversell the actual product. Many sites have high ambient temperatures, high particulate airborne contaminants and little if any air changes; all this results in elevated fluid temps and reduced efficiency on heat exchangers. Remote location of the heat exchanger is in many cases impossible. Oxidation and varnish also cause the directional valve to fail to return to neutral, the spool actually binds at neutral, ultrasonic cleaning in a heated flush/fluid solution resolves this. What kind of hydraulic equipment/application is this that needs such a low particulate count? The directional valve is a 120VAC pilot controlled valve with spring centered neutral. Gauges indicate bypass at the spool resulting in drift, off of position. Manufacturer of the directional valve is Rexroth-Size 32. I have never seen a hydraulic system that couldn't tolerate 6-10 micron particles. The directional valve in service with the 22/18/12 had visible scoring on the spool and bore of the valve. Replacement of the valve, system cleaning and fluid change, with 15/11/6, resolved the problem. The remaining concern is the VI, of the new fluid, tested 18.9% below what was specified in the product TD.
 
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Originally Posted by ABN_CBT_ENGR
Originally Posted by TravlinTech
Virgin finished hydraulic fluid. The ISO cleanliness from the OEM is unsatisfactory for the application due to a frequent function that requires minimum bypass at the spool of a directional valve when holding a cylinder in neutral when the cylinder has very high pressure on the rod end.
How exactly was this determined and by whom? If it only happens in a load state ( based on your description) then its much more likely you have components or fluid possibly not rated ( or de-rated) for that specific load. What direct causal link between fluid cleanliness to ISO and valve function did you draw and how did you verify it?
Originally Posted by TravlinTech
Low VI is a secondary issue when fluid temperature is elevated due to environmental conditions and/or high cycle times.
Issue defined in terms of what malfunction? Again, this sounds like a de-rating issue due to improperly spec'd parts/fluid or running out of design range based on your information provided.
Originally Posted by TravlinTech
Add OEM TD sheets that state given specifications but produce far from it, collectively, this makes it a challenge in delivering properly functioning equipment to end users.
That doesn't really say much but assuming this is a new application and this is in commissioning, this performance is in the "infant mortality" portion of the bath tub curve and the OEM should have people there addressing it. This has been an issue the OEM has dealt with for over 20 years, Their ME required education on cleanliness, oxidation, varnish and VI. They now have a better grasp on the impacts of low quality fluids. If this is something custom designed, re-purposed or "Frankensteined" then those who developed it need to start doing a design review or review the desired outputs against the BOM for components selected. No, regular production of 600 units per year for the last 20 years. The OEM tried different manufacturers of components since the knowledge of fluid properties was not in their tool kit, until recently. Hydraulic systems are reasonably simple and extremely robust when designed and operated properly- the conditions you are describing do not suggest or primarily point to a fluid contamination problem in any way. As you may find in the previous post, there are details that place the root cause on the fluid. This has been validated utilizing gauges at various ports on the directional vallve and/or manifold to visually show the bypass as well as visible scoring on the spool and valve body bore.
 
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Thank you for your replies. This is a unusual application where the OEM has pushed parameters of the process to extremes, almost requiring ideal conditions with the fluid and operation environment. In this application, these conditions just don't exist. It is very profitable for the OEM, since they sell directional valves in high numbers and with sub-standard, oxidized or high particulate count fluid, they have many re-orders once the new valve is contaminated. I was brought in, by the OEM, at many end users due to to premature new equipment failure or the equipment never functioning properly from start-up. Every site I walked into I was met with furious equipment owners (many wanted to return the equipment), in every case the root cause(s) of the operational issues were resolved and the equipment owner was extremely satisfied, excepting "why didn't the OEM send you here earlier". My goal, as it pertains to this discussion, is to find a fluid that can function under these, less than ideal, conditions. For obvious reasons I am not at liberty to identify the manufacturers. ISO 32, 46 or 68. 46 is the most common. ISO cleanliness 15/13/11 or better. (This can be achieved on-site) Oxidation stability >5000 Robust additive package. VI to support stability from 5 degrees to 75 Celsius. Thank you for your informative responses.
 

MolaKule

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Originally Posted by TravlinTech
...since they sell directional valves in high numbers and with sub-standard, oxidized or high particulate count fluid,
Huh? Why would they sell a sub-standard, oxidized or high particulate count fluid along with their Spools? If their spools and cylinders can't function with 0-6 miicron particles (you said you use a 6-micron filter) then they shouldn't be in business. If the problem is centered at the Spool (and this was not clear from your previous responses) then maybe the Spool bores are machined too tight or the Spool bores do not have a high enough of a bore polishing commensurate with the application. How do you know the scratches in the spool's were caused by particulate's and not bore machining? Your cause and effect linkage is weak at best. When I was designing and building high force log splitters with rebuilt Caterpillar cylinders, I used Prince Spool valves, Barnes pumps, and the Schaeffer Oil #254 hydraulic oils in ISO 68 with a 3.5 gallon reservoir and filter and i can tell you the system worked before it was shipped and the hydraulic system never had a field problem. I never ever filtered the virgin oil before adding it to the reservoir. The only problem we faced was the gas engine's carb's gumming up when the customer didn't use good fuel or drain the tank for storage. It sounds as if what we have here is a component or system design problem that has little to do with solid particles.
Originally Posted by TravlinTech
In this application, these conditions just don't exist.
What conditions are you talking about? I am having problems understanding you with your concatenated sentences that do not point to a specific subject (noun).
 
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Originally Posted by TravlinTech
The directional valve is a 120VAC pilot controlled valve with spring centered neutral. Gauges indicate bypass at the spool resulting in drift, off of position. Manufacturer of the directional valve is Rexroth-Size 32. The directional valve in service with the 22/18/12 had visible scoring on the spool and bore of the valve. Replacement of the valve, system cleaning and fluid change, with 15/11/6, resolved the problem. The remaining concern is the VI, of the new fluid, tested 18.9% below what was specified in the product TD.
Something mechanical isn't right here and it doesn't have anything to do with the fluid. Rex will tell you their valves bypass at the spool as part of the design so maybe that is a part of it and can account for drift too Scoring has a lot of causes and particle count is one of the lower ones on the list. How did you eliminate machining tolerance, thermal expansion, seal ring degradation resulting in cocking, pulsations, other fluid properties such as temp and chemical reactance? If you say resolved the problem then why is it still there? Seriously, some of your statements are somewhat disjointed and confusing as they don't follow a common theme. Nothing you have related as of yet points exclusively as a fluid related problem as the primary root cause and I'm not entirely certain of the exact failure modes you are experiencing. What are the undesirable physical actions you are experiencing and under what operating conditions and I'm sure people here can assist
 
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Originally Posted by MolaKule
Originally Posted by TravlinTech
...since they sell directional valves in high numbers and with sub-standard, oxidized or high particulate count fluid,
Huh? Why would they sell a sub-standard, oxidized or high particulate count fluid along with their Spools? If their spools and cylinders can't function with 0-6 miicron particles (you said you use a 6-micron filter) then they shouldn't be in business. If the problem is centered at the Spool (and this was not clear from your previous responses) then maybe the Spool bores are machined too tight or the Spool bores do not have a high enough of a bore polishing commensurate with the application. How do you know the scratches in the spool's were caused by particulate's and not bore machining? Your cause and effect linkage is weak at best. When I was designing and building high force log splitters with rebuilt Caterpillar cylinders, I used Prince Spool valves, Barnes pumps, and the Schaeffer Oil #254 hydraulic oils in ISO 68 with a 3.5 gallon reservoir and filter and i can tell you the system worked before it was shipped and the hydraulic system never had a field problem. I never ever filtered the virgin oil before adding it to the reservoir. The only problem we faced was the gas engine's carb's gumming up when the customer didn't use good fuel or drain the tank for storage. It sounds as if what we have here is a component or system design problem that has little to do with solid particles.
Originally Posted by TravlinTech
In this application, these conditions just don't exist.
What conditions are you talking about? I am having problems understanding you with your concatenated sentences that do not point to a specific subject (noun).
I have no answer why the fluid does not meet the manufacturers published specifications, perhaps ISO will furnish a reason of non-compliance. The spools and directional valves are from a different vendor. As previously mentioned, the equipment is operating properly after the fluid was drained, reservoir and components cleaned, new fluid was filtered and transferred into the reservoir and a new directional valve was installed after inspection. The "scratches" were not present on the spool in the pre-installation inspection, after the drift occurred two days later they were present, no other changes were made in the two day period. The "scratches" were more abundant a week later when the fluid was drained, during that time the drift increased in frequency and speed. This equipment has a reservoir containing between 300 and 500 gallons of fluid, is powered by between 50 and 225 HP, uses 1 to 3 two stage vane pumps(~40/60 GPM each), utilizes regeneration, has between a 8 and 14 inch cylinder (that has the drift issue) and operates 24/7. With clean, un-oxidized fluid with no varnish present, the equipment operates correctly-no drift. Conditions refers to high room temperature that continues to rise due to lack of air changes and airborne particulate that compromises the thermal transfer of the heat exchanger. My original question was if kidney filtration alters the VII or Di components. Thank you
 
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Originally Posted by ABN_CBT_ENGR
Originally Posted by TravlinTech
The directional valve is a 120VAC pilot controlled valve with spring centered neutral. Gauges indicate bypass at the spool resulting in drift, off of position. Manufacturer of the directional valve is Rexroth-Size 32. The directional valve in service with the 22/18/12 had visible scoring on the spool and bore of the valve. Replacement of the valve, system cleaning and fluid change, with 15/11/6, resolved the problem. The remaining concern is the VI, of the new fluid, tested 18.9% below what was specified in the product TD.
Something mechanical isn't right here and it doesn't have anything to do with the fluid. Rex will tell you their valves bypass at the spool as part of the design so maybe that is a part of it and can account for drift too Scoring has a lot of causes and particle count is one of the lower ones on the list. How did you eliminate machining tolerance, thermal expansion, seal ring degradation resulting in cocking, pulsations, other fluid properties such as temp and chemical reactance? If you say resolved the problem then why is it still there? Seriously, some of your statements are somewhat disjointed and confusing as they don't follow a common theme. Nothing you have related as of yet points exclusively as a fluid related problem as the primary root cause and I'm not entirely certain of the exact failure modes you are experiencing. What are the undesirable physical actions you are experiencing and under what operating conditions and I'm sure people here can assist
From analysis, fluid worse than 15/13/11 causes scoring of the spool resulting in bypass as evidenced by gauge placement at appropriate ports in the circuit. One example would be 1 inch of drift on a 10 inch cylinder in <5 seconds with 20/19/14 fluid and with a directional valve with scoring on the spool compared to no drift with 15/11/6 fluid with a new directional valve with no scoring on the spool. When an inspected valve was installed, it had no scoring, 2 day later the drift began and scoring was found on the spool. With clean fluid this does not occur but with 20/19/14 fluid it does. The drift problem is resolved after the fluid change, cleaning, valve change and pre filtering of the new fluid. The problem remaining is the new fluid has 18.9% lower VI than specified by the manufacturer and provided to the end user. From my perspective the fluid is the common denominator, from the beginning. A 3500 hour, 15/13/11, fluid oxidized and created varnish at approximately 5000 hours resulting in drift, understandable. The end user was instructed that a fluid change was required in addition to directional valve replacement. The valve was replaced, but the fluid change could not be scheduled for 2 months due to production needs. A different fluid, with purported improved specifications, was installed preceded by a 48 hour flush. No malfunctions were observed. The drift can be easily observed visually and through monitoring I/O. The drift reoccurred three weeks after the fluid change. The end-user changed the directional valve with drift re-occurring in 2-3 days. Analysis found the fluid to be 20/19/14 not 17/15/* as specified, the DI was also deficient. At the site, cylinder bypass was once again ruled out and the spool was found to be bound at neutral due to varnish, in addition to visable scoring. The valve and spool was cleaned in in flush mix in a heated ultra sonic tank. This resolved the binding and the drift was slightly slower. The fluid was kidney filtered and was scheduled to be changed to a third fluid with flush, cleaning and inspection. Having prior knowledge the third fluid was 20/17/15, filtration was planned prior to transfer to the reservoir. This was completed, the system flushed, cleaned, inspected, the directional valve was replaced and the equipment functioned and is still functioning properly. Analysis indicated as noted in the first addendum to the original post. The main disappointment was VI 18.9% lower than specified by a ISO 9001 manufacturer. The undesirables are cylinder drift when in a neutral hold position with maximum rod end pressure. My original question was if kidney filtration alters the VII or DI components. Filtration via a Parker cart with 10 & 40 filters, typically for 12 hours. The equipment filter is bypass filtration though a 6 or 10 micron spin on filter. Thank you
 

MolaKule

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Originally Posted by TravlinTech
...The "scratches" were not present on the spool in the pre-installation inspection, after the drift occurred two days later they were present, no other changes were made in the two day period. The "scratches" were more abundant a week later when the fluid was drained, during that time the drift increased in frequency and speed. This equipment has a reservoir containing between 300 and 500 gallons of fluid, is powered by between 50 and 225 HP, uses 1 to 3 two stage vane pumps(~40/60 GPM each), utilizes regeneration, has between a 8 and 14 inch cylinder (that has the drift issue) and operates 24/7. With clean, un-oxidized fluid with no varnish present, the equipment operates correctly-no drift. Conditions refers to high room temperature that continues to rise due to lack of air changes and airborne particulate that compromises the thermal transfer of the heat exchanger. My original question was if kidney filtration alters the VII or Di components. Thank you
And that was answered in a previous thread.
 
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MolaKule

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Originally Posted by TravlinTech
Analysis found the fluid to be 20/19/14 not 17/15/* as specified, the DI was also deficient.
Who or what Lab determined the Di was deficient and how many samples were taken?
Originally Posted by TravlinTech
The main disappointment was VI 18.9% lower than specified by a ISO 9001 manufacturer.
Who or what Lab determined the VI was 18.9% lower and how many samples were taken? Drift of the main cylinder could be caused by a bad check valve or spool leakage, depending on how the system is plumbed, I don't think you have convinced anyone here that the fluid is the root cause of your problems.
 
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Originally Posted by TravlinTech
From analysis, fluid worse than 15/13/11 causes scoring of the spool resulting in bypass as evidenced by gauge placement at appropriate ports in the circuit. One example would be 1 inch of drift on a 10 inch cylinder in <5 seconds with 20/19/14 fluid and with a directional valve with scoring on the spool compared to no drift with 15/11/6 fluid with a new directional valve with no scoring on the spool. When an inspected valve was installed, it had no scoring, 2 day later the drift began and scoring was found on the spool. With clean fluid this does not occur but with 20/19/14 fluid it does. The drift problem is resolved after the fluid change, cleaning, valve change and pre filtering of the new fluid. The problem remaining is the new fluid has 18.9% lower VI than specified by the manufacturer and provided to the end user. Actually resolved or just reset and delayed a bit? From my perspective the fluid is the common denominator, from the beginning. Possibly but I have yet to see it definitively differentiated between the actual failure mode or simply a result of the actual failure mode based on the symptoms described A 3500 hour, 15/13/11, fluid oxidized and created varnish at approximately 5000 hours resulting in drift, understandable. The end user was instructed that a fluid change was required in addition to directional valve replacement. The valve was replaced, but the fluid change could not be scheduled for 2 months due to production needs. Goodness, how long does a drain/fill take? A different fluid, with purported improved specifications, was installed preceded by a 48 hour flush. No malfunctions were observed. The drift can be easily observed visually and through monitoring I/O. The drift reoccurred three weeks after the fluid change. The end-user changed the directional valve with drift re-occurring in 2-3 days. Analysis found the fluid to be 20/19/14 not 17/15/* as specified, the DI was also deficient. At the site, cylinder bypass was once again ruled out and the spool was found to be bound at neutral due to varnish, in addition to visable scoring. The valve and spool was cleaned in in flush mix in a heated ultra sonic tank. This resolved the binding and the drift was slightly slower. The fluid was kidney filtered and was scheduled to be changed to a third fluid with flush, cleaning and inspection. Having prior knowledge the third fluid was 20/17/15, filtration was planned prior to transfer to the reservoir. This was completed, the system flushed, cleaned, inspected, the directional valve was replaced and the equipment functioned and is still functioning properly. Analysis indicated as noted in the first addendum to the original post. The main disappointment was VI 18.9% lower than specified by a ISO 9001 manufacturer. The undesirables are cylinder drift when in a neutral hold position with maximum rod end pressure. My original question was if kidney filtration alters the VII or DI components. Filtration via a Parker cart with 10 & 40 filters, typically for 12 hours. The equipment filter is bypass filtration though a 6 or 10 micron spin on filter. Thank you
Your original question has been asked and answered. It didn't happen. First of all, particulate contamination doesn't generally cause those effects that rapidly and degrade that quickly except when severely overworked. You say checked with gauges and I/O but that doesn't mean much without knowing the type/location and calibration of those things. Also were things like cooling and the presence of leaks ( leading to trapped air pockets) checked ? The act of flushing and changing a fluid is well known to mask or otherwise give the "illusion" of "healing" some problems. If I read you right and the problem eventually comes back then that indicates neither is the actual failure mode. ( if they didn't come back- problem solved, right?) I still see your claims on failures pointing toward enter a mechanical issue or a component rating issue ( possibly inadequate cooling based on your varnishing comments and the speed these things seem to happen) Be happy to assist you in any way I can but I still don't see a definitive case of a fluid problem exclusively
 
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