34110216 lubrication hydraulic fluid cleanliness

8/8/2019 34110216 Lubrication Hydraulic Fluid Cleanliness

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INTRODUCTION

Anyone who has dealt with hydraulic sys-tems for any length of time will admit thathydraulic systems have evolved from a sim-plistic, crude state into extremely complexsystems in a relatively short time. Someessential reference points in the develop-ment of hydraulic systems include the build-

ing of the pyramids and the scientificresearch of Blaise Pascal and AlbertEinstein. The first documented use ofhydraulic technology applied as a labor sav-ing technology occurred during the construc-tion of the Egyptian pyramids. Over a thou-sand years later in the 1600s, Pascal dis-covered hydraulics as a science. Throughthat discovery came Pascals Law whichstates, Pressure exerted on a confined fluid

is transmitted throughout the fluid, undimin-ished, in all directions and acts with equalforce on all equal areas.

Three hundred years later in the early1900s, Albert Einstein said this abouthydraulics, Why is it that this magnificentapplied science, which makes life easier andreduces work, bring us little happiness? Thesimple answer runs because we have notyet learned to make sensible use of it.

One look at the hydraulics equipmentassociated with the PLC (programmable

logic controller) controlled robotics in usetoday is all it takes to know that todayshydraulic systems are very sophisticatedand that we are now taking advantage of thismagnificent applied science.

Unfortunately, hydraulic fluid handlingpractices have not advanced at the samerate as the equipment. For that reason,much of todays sophisticated hydraulicequipment fails prematurely and does not

live up to its projected performance poten-tial. Close examination of failed componentshas revealed that more than four times as

A Technical Publication Devoted to the Selection and Use of Lubricants

Published By

Texaco Inc.

2000 Westchester Avenue

White Plains, NY 10650

LUBRICATION

Volume 87 Number 1 January, 2001

To request a new subscription or to report a change of address (enclose mailing label),

please write to: Robert J. Taylor, Texaco Inc., 1111 Bagby Street, Houston, TX 77002;

or by e-mail: [email protected]

Copyright2001 by Texaco Inc. All Rights Reserved.

Materials may not be reproduced or reprinted without written permission of Texaco Inc.

TECHNICAL EDITOR: LYNNE L. MEGNIN

MANAGING EDITOR: JAMES B. COLEY

PRODUCED BY: BAKER PRINTING, BAKER, LA

HYDRAULIC FLUID

CLEANLINESS


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many hydraulic system failures are causedby improper fluid condition than all othercauses combined. This fact makes it imper-ative that the message concerning theimportance of hydraulic fluid cleanliness and

how to achieve a state of cleanliness beconveyed to hydraulic fluid users. This arti-cle will examine the meaning of cleanliness,discuss contamination sources, and offersolutions to promote fluid and system clean-liness.

HOW CLEAN IS CLEAN?

Cleanliness is a relative term, which

prompts us to ask, How clean is clean?The degree or level of cleanliness in oneapplication may not be sufficient in another.For example, the required cleanliness for thefluid in a hydraulic floor jack is substantiallydifferent than for the fluids used in manufac-turing machine robotics; yet, they are bothhydraulic systems. For this reason we mustdefine clean.

The term clean, as referred to in this arti-cle, describes the cleanliness of thehydraulic fluid and the hydraulic system.Clean hydraulic systems are defined by aquantifiable, measurable level of particulate,foreign matter, other hydraulic fluids or for-mulas, and water or moisture. The concen-tration of these contaminants determines thedegree of cleanliness of the hydraulic fluid.

The importance of maintaining a cleanhydraulic system cannot be ignored.Because of the large number of contamina-

tion related system failures, the NFPA(National Fluid Power Association) and ANSI(American National Standards Institute)have established minimum system cleanli-ness standards. From the use of thesestandards, target cleanliness levels can beestablished for each application. The basisof the individual targets must be set to themost sensitive component in the system.

The most common cause cited for denialof warranty claims in hydraulic systems iscontamination. Many original equipmentmanufacturers are now predicating the

equipment warranty on the continuous main-tenance of specified cleanliness levels. If asystem reaches unacceptable cleanlinesslevels and the condition is not quickly cor-rected, the warranty will be voided.

TYPES OF CONTAMINATION

Contamination can take several forms,including, but not limited to:

1. Metallic Particulate is normally theby-product of metallic componentwear. Environmental dust, dirt fromconstruction or maintenance, oranything that can breakdown into

small pieces can also be classifiedas particulate. Circulation of a slurryof fluid and particulate will generateeven more particulate from abra-sion. The particles generated inter-nally will be harder than the sur-faces from which they came, thusbecoming even more damaging tomachine surfaces.

2. Foreign Materials such as piecesof gasket material, gasket sealerssuch as silicone sealant, damagedO-rings, debris from the construc-tion or assembly process, weldingbuckshot, and material introducedduring start-up and normal opera-tion all contribute to contaminationof hydraulic systems.

3. Other Hydraulic Fluids orFormulas are normally introducedduring the filling process. This con-

tamination can come from theequipment used to transferhydraulic fluid from storage contain-ers to the system. Hand pumps,hoses, storage drums, and vesselsare all typical sources of fluid con-tamination.

4. Water can form through the simpleprocess of atmospheric condensa-tion in a vented-to-atmosphere sys-tem. Maintenance personnel wash-ing down an area can introducewater into a hydraulic system by


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inadvertently directing the waterhose at a vent on a reservoir, orwashing a reservoir that is not com-pletely sealed.

5. Gases caused by aeration, cavita-

tion, or poor design can contaminatea hydraulic system. Sources forgases can be leaking pump seals,pump suction side leaks, or the oilbeing returned to the bulk fluidabove, rather than below, oil level.

SOURCES OF CONTAMINATION

NEW HYDRAULIC OIL

New hydraulic oil is formulated to optimizesystem performance by:

Being non-compressible Reducing friction Reducing component wear Transferring heat easily Separating water easily Releasing entrained air quickly Providing a viscous seal

Each oil formulation is tested for all ofthese attributes and several performancecharacteristics. It is also tested for compati-bility with other hydraulic fluids. All of thesetests are performed with clean, dry fluids,and there is not a test that includes contam-ination with particulate and/or water.Therefore, for the fluid to perform in ahydraulic system the same way it performedin the tests, it must be kept clean and dry.

For those who might think there should be

a test that includes particulate and water,there are simply too many different types,amounts, and combinations of particulateand fluids that occur in hydraulic systems forthis to be feasible. The thin fluid film is whatthe moving parts are supposed to be ridingon. However, if the particulate is larger indiameter than the thickness of the fluid film,it is easy to see that the moving parts will beriding on the particulate rather than the fluidfilm. Any test that might be developed whichincludes particulate would not be reflectingfluid performance.

There is a common belief among hydraulicfluid users that if the hydraulic fluid supplierwould just deliver clean fluid, there wouldnot be a problem. Unfortunately, excessiveparticulate contamination can occur from

many sources. Every time a hydraulic fluid ishandled the particulate contaminationincreases. For example, particulate can beintroduced when new hydraulic oil is blend-ed, pumped, packaged, transferred,pumped into a new system, or added to anactive system. These are not the onlysources for particulate. Each source con-tributes a little and eventually the level ofcontamination can become excessive if

measures are not taken to control it.It is true that new hydraulic fluid should be

clean. However, a target cleanliness levelmust be determined first. The fluid supplieris trying to supply a fluid that is cost com-petitive and will perform the desired task formany, many applications. Supplying fluidsthat are totally particulate-free would drivethe cost of the fluid excessively high. In real-ity, the only point at which the particulatelevel is truly critical is in the hydraulic systemitself. For that reason it is recommended thatthe required hydraulic fluid cleanliness levelbe determined and that target be met as thefluid is pumped into the application.

Even if the new hydraulic fluid is cleanwhen it is delivered, if it is pumped into astorage tank that is grossly contaminated,any efforts to deliver clean fluid will be wast-ed. Many end users tend to overlook thecleanliness of their own storage tanks. They

also fail to realize that their storage tankscan be a major source for contamination ifthey are not vented properly. Also, if the stor-age tanks are equipped with steam coils, asmany of them are, they occasionally leaksteam condensate into the hydraulic fluid.

The following is a generic, logical path toinsure the best opportunity for favorable fluidperformance:

1. Insure that the proper fluid and vis-cosity are being used.

2. Insure that the storage container isclean and dry.


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3. Insure that the storage container isvented properly by using the appro-priate vent filter.

4. Insure clean fluid is delivered byestablishing a reasonable target

cleanliness level and have the fluidfiltered to the target level, or cleaner,when it is pumped into the storagetank, tote, or other storage contain-er.

5. Read the certificate of analysis (C ofA) to determine the moisture contentof the new fluid.

6. Establish the appropriate targetcleanliness level and circulate the

fluid in the storage container througha kidney loop filtration system untilthe target is met and can be main-tained.

7. Filter the fluid any time it is trans-ferred from the storage container.

8. Filter the fluid as it is transferred intothe active system.

9. Determine and maintain the systemtarget cleanliness level with eitherthe filtration designed into the sys-tem or by using a kidney loop filtra-tion system attached to the hydraulicsystem.

10. Set-up a monitoring schedule andsubmit representative samples ofthe fluid for testing.

11. Insure that everyone that can affectthe test results sees and under-stands the test results, including theclean-up people and the person that

enters the results in the computer orother data monitoring form.

If this path is taken, the particulate level ofthe new fluid will be reduced because thechecks and balances will be in place to cap-ture any contamination before it gets to theactive system.

HYDRAULIC SYSTEM CONSTRUCTION

When a hydraulic system is constructed,contaminants are produced by the construc-tion process. Cutting, grinding, welding,

excess gasket sealers, excess bolt threaddressing, and general construction atmos-pheric dust all contribute to an unclean sys-tem. A newly constructed system must bethoroughly cleaned and flushed to insure

maximum cleanliness. Introducing new,clean hydraulic fluid to a dirty system will dolittle, if anything, to slow component wear orprevent system failure.

INGRESSED MATERIALS

Contamination of a hydraulic system alsooccurs from ingression of materials. Anexample of ingressed material is a reservoir

which has a 3 diameter oil return line, enter-ing a 10 diameter hole in the top of thereservoir. The 10 hole exists to allow forreturn line movement during operation. Thisopening offers an excellent point for contam-ination ingression. Particulate in the atmos-phere, water from area wash downs, andmanufacturing debris will find their way intothe opening and contaminate the fluid reser-voir. A simple rubber or leather boot attachedto the surface of the reservoir and the returnpipe to fill the gap will solve the problem andreduce fluid contamination.

In order to prevent ingress of particulatethrough the system vent, the proper systemvent must be installed. As hydraulic systemfluid demands change, the fluid level risesand falls causing air to enter and exit thespace above the fluid level in the reservoir.This action is commonly referred to asbreathing. If the vent is not properly filtered,

particulate from the atmosphere will enterthe vent hole and contaminate the fluid.

Another example of particulate ingress ison the rod end of a hydraulic cylinder. As therod is extended, it is wiped off by a wiper andthe oil seal. However, a very thin oil film willstill be present and air borne particulate willdeposit on the extended, wet rod. Whenthe rod is retracted, some of the particulatewill get past the seal and wiper and bewashed off the rod by the fluid inside thecylinder. The better the condition of the seal,the less likely this will be a problem.


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INTERNAL GENERATION

Internal generation of contaminants isunavoidable in an operating system. Normalwear of moving parts causes particulate that

will serve to reduce the efficiency of the sys-tem. If not dealt with, the normal wear willdegrade the system and its components.Particle concentrations in hydraulic fluid areabrasive. Abrasive wear to componentsincreases the particle concentrations in thefluid. Correct filtering and properly locatedfilters can dramatically reduce their damag-ing effects.

MAINTENANCE ACTIVITIES

Many times maintenance activities per-formed on hydraulic systems produce con-tamination. Opening a reservoir in anextremely dusty environment will cause adramatic increase in particle count.Disassembly and re-assembly of compo-nents often introduces foreign material intothe system. Excess gasket dressing, pipethread sealant, thread cutting oils fromreplacement piping, and old gasket materialoften find their way into the hydraulic sys-tem. The paper-like qualities of gasket mate-rial serve to block the surface of filter mediaand reduce the efficiency of the filter. Evensmall quantities of thread cutting fluid or anyforeign fluids can negatively impact thehydraulic fluid formulation. Any change tothe hydraulic fluid that alters the compress-ibility, lubrication qualities, or particulate

concentrations will degrade the efficiencyand life of the system.

HEAT

Heat is another form of fluid contamina-tion. Most hydraulic fluids are not designedto operate at excessively high temperatures.In fact, if the hydraulic fluid is allowed toexceed critical temperature, the chemicalstructure changes, viscosity varies, andusable life is drastically reduced. This criticaltemperature is typically 140F (60C). It has

been said that for every 18F (10C) of fluidtemperature increase above the critical tem-perature, the fluid oxidation rate doublesand the fluid life is cut in half. This numbercan change both for the better or worse,

depending on the fluid in question, with theextremes being synthetics and biodegrad-ables. Heat sources include:

Improper system design Pump cavitation or aeration Wrong fluid Wrong fluid viscosity Ingression of air and compression of

the entrained air Wrong application of equipment

Failure of or absence of heatexchanger

Inadequate temperature differentialbetween ambient and heatexchanger

Lack of shrouding of exchanger toforce direction of cooling air

Forcing too much oil through therelief valve (poor system design)

MOISTURE

Moisture is a very common form of con-tamination in hydraulic systems. Quite often,the moisture comes from the atmospherearound the reservoir. The moisture condens-es in the vapor space above the oil level inthe reservoir on the cooler interior metalwalls and roof of the reservoir. If the interiorwalls of the reservoir are not protected ade-quately by an appropriate coating, the mois-

ture will cause rust to form. The rust willflake off into the hydraulic fluid where it willbe carried into the inlet of the pump and dis-tributed throughout the entire system.

Reservoir vent filters can aid in reducingor eliminating the introduction of moisturefrom the atmosphere by incorporating waterbarrier technology in their filter matrix. Watercan also enter the system through inspec-tion holes and through other service open-ings, if the opening covers are not replacedand resealed after each maintenance event.Rain and area wash downs can introduce


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water into hydraulic systems through theseunsecured openings. Water and oil heatexchangers, which should be pressure test-ed before placed in service, are sometimesused to control the hydraulic fluid tempera-

ture. If the tube bundle in the exchangerleaks, water will enter the hydraulic fluid andbe distributed throughout the system.

Poor fluid storage practices can oftenintroduce water into a hydraulic system.Many times, drums of hydraulic fluid arestored near a hydraulic system for conven-ience. The drum is usually unprotected fromthe environment, rain, dust, dirt, and areawash downs. The top of the drum becomes

contaminated with all these materials, andwhen opened to add fluid to the system, thecontamination flows directly into the opendrum. When drums are left upright the head(top) of the drum is often filled with rainwa-ter. If the drum opening is not sealed prop-erly, the naturally occurring heating andcooling effects of the drum can cause wateron the head of the drum to be pulled throughthe threads and into the fluid.

If free water is allowed to remain in thehydraulic system, bacterial growth canoccur. Once excess moisture is present, allthe conditions required to create such areaction inside a normal hydraulic systemare present. Moisture, air, oil, and heat cancreate some very undesirable reaction by-products such as odor, rust, chemicalchanges to additives, and increased oxida-tion rate. Every effort should be made toreduce the amount of moisture in a hydraulic

system. The corrosion damage caused bymoisture contamination contributes to sys-tem failure, increased maintenance costs,and more frequently occurring downtime.

COMMON FAILURE CONDITIONS

INADEQUATE DESIGN

Existing hydraulic systems with contami-nation problems are frequently caused byinadequate design. System design failuresare often the most difficult to resolve. A real

cost analysis must be administered to deter-mine if a redesign of the system is the cor-rect solution.

Consider the following example: The prob-lem is excess contamination, overheated

fluid, and poor maintenance practices. Thesystem reservoir is located under the electri-cally heated equipment where the ambienttemperature is approximately 135F. Thearea is washed down frequently with water.

The high ambient air temperature condi-tion was created when several units wereconfigured to reduce heat losses and reduceelectrical power requirements. The originaldesign called for the reservoirs to be posi-

tioned so that adequate heat dissipationcould be accomplished by ventilating thespace. It is important at this point to remem-ber that one of the functions of the reservoiris heat dissipation through the walls. Theimproved heat loss reducing configurationof the machines has caused the majority ofthe hydraulic system failures. Because thearea is so hot, it is difficult to get mainte-nance personnel to enter the area to work.Those who enter the area cannot remainvery long. Hydraulic fluid leaks persist andthe oxidation rate increases because thehigh ambient temperatures reduce heat radi-ation capability.

The return line to the reservoir also intro-duces fluid into the reservoir above the fluidlevel. This causes air to become mixed intothe fluid. These air bubbles enter the pumpand are compressed. This results in adiabat-ic compression, the results of which can be

seen in the following examples: Air bubble at 70F and 14.7 psi:

-Compressed bubble to 1,000 psi =over 1,300F; a 985 psi increasecauses a 1,230F temperatureincrease.-Compressed bubble to 10,000 psi =3,000F; a 9,930 psi increase caus-es a 2,930F temperature increase.

The heat generated by adiabatic compres-sion occurs at the surface of the bubble anddissipates quickly in the fluid. However, if itis allowed to continue, the effects are mani-


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fest as a steady increase in overall systemtemperature. Once this starts occurring,heat exchange capabilities of the systemmust be adequate to handle the extra heat.Handling of excess heat translates into

money spent unnecessarily.One of the functions of the reservoir is to

radiate heat. It is often thought that if thereservoir is large, then heat exchangers arenot necessary. Here is an example of whythat thinking is flawed. If a 200 gallon reser-voir in location with a 30F temperature dif-ferential (ambient cooling air is approximate-ly 30F cooler than the oil during stableoperating conditions), the reservoir can only

shed approximately one-half horsepower(Hp) of heat.

As fluid temperatures increase, the lubri-cating qualities, viscosity, and film thicknessof the fluid diminish resulting in componentwear, particulate generation, and systemfailure. The combination of high ambienttemperatures, inadequate maintenance, andadiabatic compression produce frequent

component failures, increased maintenancecost, and excessive downtime resulting inreduced profits.

In this example, it is clear that a compari-son of the savings realized by the new heat

loss reducing design and the increased costassociate with hydraulic system expenseand down time is needed. At least superfi-cially, it appears that this system is doomedto fail completely.

One of the best solution to an inadequatedesign problem, such as the one shown inFigure 1, is to relocate the machines so ade-quate reservoir heat radiation and oil coolingcan occur. However, the production require-

ments and budget of the facility cannot toler-ate shutdown, redesign, and relocation.Situations like this demonstrate the need forserious consideration of target cleanlinesslevels and system maintenance during thedesign phase of any hydraulic system. Thesystem in Figure 1 could be significantlyimproved by the addition of a heat exchang-er on the hydraulic fluid reservoir.

Control Panel Control Panel

HydraulicReservoir

(below press)

Control Panel

Ambient Temperature in this area(Hydraulic System Cooling Air)

~ 135F

ELECTRICALLYHEATED

HYDRAULICPRESS

ELECTRICALLYHEATED

HYDRAULICPRESS

ELECTRICALLYHEATED

HYDRAULICPRESS

ELECTRICALLYHEATED

HYDRAULICPRESS

ELECTRICALLYHEATED

HYDRAULICPRESS

ELECTRICALLYHEATED

HYDRAULICPRESS

PLASTIC CURTAIN PLASTIC CURTAIN

HydraulicReservoir

(below press)

HydraulicReservoir

(below press)

HydraulicReservoir

(below press)

HydraulicReservoir

(below press)

HydraulicReservoir

(below press)

Control PanelControl Panel Control Panel

Figure 1 - Inadequate Design


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OTHER FLUIDS

Ashless (Zinc-free) Fluids

In some cases, different hydraulic fluid

formulations can contaminate the systemby creating reaction by-products. If a useris currently using a zinc-containinghydraulic fluid and decides to replace itwith an ashless (non-zinc containing) fluid,the entire system must be drained andflushed thoroughly. A mixture of a zinc-containing fluid and an ashless fluid cancause a reaction, which can form salts thatwill eventually plug system filters. This is

primarily a function of the difference in pHbetween the two products, caused by dif-ferent additive chemistries.

The fluid and equipment suppliersshould be consulted concerning properflushing procedures and cleaning methodswhen the user switches from one fluid toanother.

Mineral Oil and Synthetic Fluids

Another problem can occur when ahydraulic system is switched from a miner-al oil based hydraulic fluid to a syntheticfluid. If the entire system is not drainedand flushed thoroughly, the expectedadvantages of the synthetic fluid may becompromised by the presence of the min-eral oil. Changing hydraulic fluid types canonly be done properly if the system is thor-oughly drained and cleaned of all the other

fluid prior to introducing a new fluid.There can also be adverse effects from

introducing a synthetic fluid to a systemthat has seals that are not compatible withsynthetics. The effects of the fluid on elas-tomers should be readily available fromthe system designer, seal manufacturer, orthe fluid supplier.

Biodegradables

Another cause for concern is when min-eral oils are replaced with biodegradable

fluids. There is an old proverb that states,Be careful what you ask for, because you just might get it. The same holds truehere for biodegradable fluids. The primaryfocus during biodegradable oil formulation

is making a product that can degrade eas-ily. It is feasible that some of these fluidscould degrade while in storage, beforeeven being introduced to the hydraulicsystem.

It is important to understand that allhydraulic fluids are biodegradable. In fact,everything is biodegradable. It is just amatter of what conditions are necessaryand how much time it takes something to

biodegrade.With respect to hydraulic fluids,

biodegradability is simply a matter of howquickly it changes from its original forminto a chemical form that is environmental-ly innocuous (water, carbon dioxide, min-eral salts, and biomass). For something tobe classified as readily biodegradable itmust meet accepted standard test criteria,which specifically state how quickly itbecomes environmentally innocuous.

Unfortunately, all the components need-ed to promote biodegradability such asheat, entrained air, and water are com-monly present in hydraulic systems. Thispresence directly affects the rate at whichbiodegradable fluids break down. Greatcare must be taken to remove air andwater from a system containing biodegrad-able fluids. Heat buildup must also be keptto a minimum.

If the system is not properly controlled,biological growth and extremely noxiousodor will result. At this point, the systemmust be shutdown and thoroughly cleanedin order to meet biological cleanliness lev-els. Above average temperature control ofbiodegradable fluids should also be used.Biodegradable fluids should operate attemperatures at or below 140F. If the fluidis allowed to exceed 140F, oxidation ofthe fluid increases rapidly and the fluid lifeis shortened dramatically. Changing tobiodegradable fluids requires a thorough


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cleaning of the system. Failure to properlyclean the system can increase biodegrad-ability and increase toxicity of the fluid inthe system, especially if a mixture of otherfluids, air, and water can change the

biodegradability of the fluid to an undesir-able level.

OXIDATION

Oxidation is another source of hydraulicfluid failure. Oxidation occurs when oxy-gen reacts with the oil to form a multitudeof compounds. The first reactions formunstable hydroperoxides. The hydroperox-

ides react to form alcohols, aldehydes,ketones, acids, and oxy-acids that are sol-uble in oil. These acidic products increasethe viscosity of the oil and can be corro-sive to metal in the system.

Polymerization and condensation reac-tions produce insoluble gum, sludge, andvarnish. These products serve to plugopenings, increase wear, cause the sys-tem to become sluggish in operation, andreduce clearances making the system ulti-mately inoperable.

Temperature is a primary accelerator ofoil oxidation, as well as moisture, dirt,metal particles, paint, joint compounds,and insoluble oxidation products. The rateof oxidation will approximately double forevery 18F (10C) rise above 140F (60C)in fluid temperature. The life of thehydraulic fluid is cut in half with just 1%sludge concentration because contamina-

tion makes the oxidation rate double.Metal particulate, such as copper, iron,

nickel, brass, and steel, are known to pro-mote catalytic reactions and accelerate oiloxidation. This catalytic reaction is furtherenhanced by the presence of water. In thefirst stages of oxidation, both the viscosityand the neutralization number of the oilwill increase. The neutralization number iscommonly used to determine when oil oxi-dation has progressed to the point wherethe oil becomes aggressive and should bereplaced. The varnishes that are formed

during oxidation will deposit on shinymetal surfaces, such as directional valvespools and the internals of servo valves.This will result in sticky operation and/orsluggish performance. The sticking of

directional valve spools causes more elec-trical solenoid failures than all other caus-es combined.

SETTING TARGETCLEANLINESS LEVELS

Target cleanliness levels, in this context,represent the maximum contaminationlevels at which hydraulic fluids can be

expected to function as designed andachieve optimum equipment performanceand reliability. The cleanliness targetmust meet the requirements of the mostsensitive component in the system com-bined with system pressure and safetyconsiderations.

The consequences of failing to set targetcleanliness levels for every hydraulic sys-tem, and not exceeding those targets, isreduced system life, decreased fluid life,and greater safety risks. Down time andoverall system operation and maintenancecosts will also be higher.

Particle contamination is typically madeup of sand, silica, loam, tiny metal parti-cles, wood fibers, rags, oil absorbentmaterials, or any other solid material thatcan be broken down into small particles.Particulate can cause problems, such asblocking small openings, if the particles

are too large. This can be especially harm-ful if the opening is a control orifice. If theparticle is about the same size as theclearances in pumps or motors, it mayenter the opening and then becometrapped between the moving surfaces.This can cause abrasive wear, which pro-duces more particulate that further con-taminates the system.

It is also important to recognize that veryfew particles are round. They are usuallyirregular in shape and have many sharpedges that create more system wear as


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they are circulated. The particulates lodgethemselves in valves, which can result inburned out electrical solenoids.

Very small particles referred to as siltflow through the system without much

restriction. Due to high velocity streamsand directional changes in flow, impinge-ment of these particles on surfaces causeserosion that increases the clearancebetween moving parts and in control ori-fices. This promotes internal leakage andgenerates additional wear particles that

further degrade the system. This has anegative impact on system control per-formance and repeatability. The velocitythrough temporary or permanent orificeschanges with plugging or erosion as the

size of the hole changes. As the holechanges in size, the velocity of the fluidand particulate passing through it alsochanges. Velocity change results in achange in the erosion dynamics.

The size of particulate contaminationvaries from visible materials to the unaided

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34110216 lubrication hydraulic fluid cleanliness

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