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Servo Technology & ResearchFiltration – Flushing & Commissioning Seminar

Hydraulic Servo Systems EIS Seminar 25th October 2013


Servo Technology & Research

Fluid Cleanliness & Filtration Servo Systems

Possibly a different and more effective approach

Contamination comes in many formsParticulateChemical

OxidizationAir & Gas

Fluid Degradation

“RAPID REMOVAL OF CONTAMINANTSINTRODUCED DURING ASSEMBLY,

SERVICE & MAINTENANCE

A Key Requirement for Servo Systems

The reasons why?

From The Start! Commissioning & Flushing

Objectives -


The Key Issues SurroundingFiltration – Servo Systems What we will

cover today• Why do we need filters?• What cleanliness standards should we work toward for the system

before its put it into service?.• What filters ratings do we need to adopt for Flushing?• What Cleanliness Standards do we need to reach after Flushing?• How long do we leave the system in the Flushing Mode? Not 48

Hours as commonly quoted!!!• How do we know when we have truly removed all the debris. • How should we plan the flushing process when we commission

systems?• Thereafter - Cleanliness Verification Programmes – For the End-users


Why do we need to use Filters


Component Clearances

The operating clearance is not equal to the machine clearance (fit) of the bearing but depends on the load, speed, and lubricant viscosity. A lubricant film separates the surfaces to prevent metal to metal contact.

5µm

5µm

MachineClearance

10µm

Load,No Motion

Load and Motion and Lubricant

9µm

1µm

Journal Bearing

Rolling Element Bearing

Cage LubricantFilm

Journal Bearings


.

Bearings–Roller–Journal–Hydrostatic

GearsDynamic SealsPumps

–Gear–Tip to Cut In Track–To Side Plate–Matching

Vane–Tip to Cam Ring–Side of Vane

–Piston–Piston to Bore–Timing Plate

Valves–Directional–Poppet–Servo

0.1 – 1 micrometres0.5 – 100 micrometres

1 – 25 micrometres0.1 - 1 micrometres

0.05 – 0.5 micrometres

0.5 – 5 micrometres0.5 – 5 micrometres0.2 – 5 micrometres

0.5 – 1 micrometres5 – 13 micrometres

5 – 40 micrometres0.5 – 5 micrometres.

2 – 20 micrometres 10 – 40 micrometres2 – 4 micrometres

Dynamic ClearancesModern Hydraulic

Systems.

Rolling Element Bearing

Cage LubricantFilm

ABRASION ADHESIONFATIGUE

Loss of Usefulness

Obsolescence (15%)

SurfaceDegradation

(70%)

Accidents(15%)

Corrosion (20%) MechanicalWear (50%)

Equipment Life Expectancy Factors


It is a fact!

Any damage incurred when a system starts up, never recovers.

The initial damaged sets the life potential.


Bearing FatigueLife Extension

0 10 20 30 40 50

Filter Rating (Particle size, µm, where Beta = 200

0

2

4

6

8

10

12

14M

illio

ns o

f Cyc

les

To B

earin

g F

atig

ue F

ailu

re Dr. P Macpherson's

Curve - Imperial College/Westland

Helicopters

The Beta 2=75 micron region

• NAS 12 ISO 21/19/16• New oil as delivered in barrels


Fresh oil,delivery in barrels

NAS 7 ISO 18/15/13

Fresh oil,delivery in mini containers

NAS 5 ISO 16/14/11

Required for modernhydraulic systems

Fresh oil,delivery in tank trucks

NAS 12 ISO 23/21/18 NAS 9 ISO 21/18/15

.


Fatigue Wear OnBearing Surfaces

LOAD

Particle caught

STAGE 1



LOAD

Surfaces dented, cracking initiated

STAGE 2



LOAD

After 'N' fatigue cycles, cracks begin to spread

STAGE 3



LOAD

Surface fails, particles are released

STAGE 4


Wear on Roller Bearings– Spall effect in a deep groove ball bearing


Dynamic Clearances- Typical Valve

Dynamic ClearancesServo valve 2 - 4 µmProportional valve 2 - 6 µmDirectional control valve 2 - 8 µm


Erosive WearParticles impinge on the component surface or edgeand remove material due to momentum effects

Effects:•• Dimensional ChangesDimensional Changes•• Leakage Leakage •• Reduced EfficiencyReduced Efficiency•• MORE WEARMORE WEAR

Servo Valves

2003 Servo Technology & Research

First Stage & Pilot

Second Stage

Service Ports

Return GalleryPressureRegions

Typical Travel of SpoolW ithin the Bushing = 0.5mmMachine Clearance = 2.5 micronsDynamic Clearance /0.5


Eroded Spool Metering Edge

Contamination Erosion


Valve internal “Last Chance Filters”We discussed with one customer why the servo valves was contaminated

because he had a 3 micron filter directly in front of the servo valve!


What Cleanliness Standardsdo we need to work to?

What filter ratings do we need to adopt to achieve the desired

cleanliness standard?


What Filter Ratings do we need to work to?

To achieve the required cleanliness standards.


At Star we do not Sell Filters

• We have no desire to promote business by selling new filters or replacement filter elements.

• Our aim is simple, extending the operational life of servo systems internationally where a great deal exist already. Hence the USA, Japan, Germany and Asia are our largest growing markets.

Filter Cleanliness & Micron Weighting Selection Programme.

• Applying the science to match cleanliness standards to filter ratings.

• At Star we undertake this review with OEM’s and Users alike.

• We don’t want to keep on repairing the same servo valves again and again!

• That’s just not our business.

• There is no single fix but we undertake this confidentially customer by customer.


Cleanliness Standards

Cleanliness Standards

• Filters are rated in Microns.• Cleanliness Standards are not rated in

Microns.• Cleanliness Standards are determined by the

system environment needs & component characteristics.

• There is no such thing as a 2, 3, 5 or 10 micron systems.

• Cleanliness Standards relate to the amount of particles by number in a given quantity of oil

International Cleanliness Standards

ISO 4406 (1999) & NAS 1638are the most common(Military work to Def Standards)

ISO4406 Cleanliness Codes 1999

The code relates to the number of particles equal to or greater than 4 6 & 14 micrometers in a fluid sample of 1 milliliter volume

ExampleISO4406 Code

16/14/12

Particle Concentration(Particles per Milliliter) Range Number

40,000 - 80,000 2320,000 - 40,000 2210,000 - 20,000 215,000 - 10,000 202,500 - 5,000 191,300 - 2,500 18640 - 1,300 17320 - 640 16160 - 320 1580 - 160 1440 - 80 1320 - 40 1210 - 20 115 - 10 102.5 - 5 9

It is normal practice to take 100 ml of oil from a system when establishing a cleanliness code

>4 µ = 330 particles>6 µ = 100 particles>14 µ = 30 particles

ISO 4406 Cleanliness Codes

2481.63.26.41.32.55248

1.63.26.4

1.32.55

1234567891011121314151617181920

1

10

102

103

104

105

5 10 15 20 25

Ra n

ge N

u mbe

r

Nu m

ber o

f Par

t icle

s pe

r 100

ml >

ind i

cate

d si

z e

(µm)

16/14/12

The code measures the number of particles equal to or greater than 4, 6 and 14 micrometres in a fluid sample of 100 milliliters of oil.

<4 micron count between 320,000 & 640,000<6 micron count between 80,000 & 160,000

<14micron count between 2,000 & 4,000


Nominal RatingThis is a arbitrary form of measure stating a micrometer value, based on manufacturers claimed test performance which is not published or qualified. Due to a lack of sound comparably data, this rating is depreciated.

Absolute RatingThis relates to the largest none deformable spherical particle that will pass through a filter under specified test conditions. This is indication of the largest pore in the filter element.

Filtration Ratio (ßX)The ratio of the number of particles equal to or greater than a given size (x) in the influent fluid to the number of particles equal to and greater than the same size (x) in the effluent fluid.

Filter Ratings


Filter Ratings – How They Are Determined

Beta Values are in fact Box Ratio’s stated at any given micrometer size.

Simply:-Number of particles upstream of the filter

Number of particles downstream of the filter

1,000,000 Upstream13,000 Downstream Box = 75 (98.7%)

1,000,000 Upstream5,000 Downstream Box = 200 (99.5%)

Any filter, no matter what its micron rating should haveminimum Box of 75


Multi-pass Performance Test

Flowmeter

DownstreamSample

AC Fine Test Dust Slurry

UpstreamSample

AutomaticParticleCounter

Dp GaugeReservoir

Test Filter

AutomaticParticleCounter

Contamination LoadingCurve

D p switch activates

T1 T2Service Hours

Ele

men

t DP

(Bar

)

5.0

4.5

Bypass valve opens

Comparison between the sizing of A good versus a bad filter

With the same rating


Results of Contamination Analysis• Main Tank = ISO 4406 18/16/13NAS 1638 Class 7

• After XXXXX ? Pressure Filter ISO 4406 22/20/16NAS 1638 Class 11

.Well Known


Eroded Spool Metering Edge

Contamination Erosion


Flushing

• Minimise contaminant introduction• Components• System pipework• Reservoirs• New Oil

• Protect dynamic clearances from particle release during start up

•With Servo’s, always fit a flushing plate. •If needed also fit hand operated flush valves

Initial Flushing Objectives

• Proper flushing of the oil to the required cleanliness level or better greatly reduces, if not eliminates catastrophic failures normally associated with initial system start-up. It is strongly recommended to flush to one class cleaner than systems operational requirement• The use of Beta x = 1,000 filters is key.

•Qualify Cleanliness where possible before fitting the Servo Valve.

Flushing

FlushingP

artic

les

/ 100

ml >

5µm

Flushing hours

No turbulence in Pipework

Turbulent flow now achieved. = rapid release of debris.

Reduced flushing time = Reduced costs

Case Study John Brown GlasgowGE Turbine Control System

The Flushing Cleanliness Specification


Sample of debris left inside a hose froma leading supplier After Firing Cleaning Pellets


Sample of debris left inside a hose froma leading supplier – After Firing Cleaning Pellets

Reynolds Number

Reynolds Number Calculation

Where : Re = Reynolds Numberd = Inside pipe dia. (mm)v = Fluid viscosity (cSt)Q = Flow rate (L/min)

Re = 21,200 Qvd


Flushing and Reynolds Calculation Sheet

FLOW VARIATION & TEMPERATURE VARIATION

Reynolds = 21220 x Q (l/m) 21220 x 50 1061000

Vis (c/St) x ID Tube (mm) 42 x 25 1050 1010.48 Answer

Reynolds = 21220 x Q (l/m) 21220 x 100 2122000

Vis (c/St) x ID Tube (mm) 20 x 25 500 4244.00 Answer

Reynolds = 12205 x Q (gpm) 3778 x 15 56670

Vis (c/St) x ID Tube (Inch) 30 x 2 60 944.50 Answer

The Effects on Reynolds Doubling the Flow & Temperature

1

Filtration for Servo’s

• In reality the cleanliness for the system as a whole should be determined.

• For good life the recommended level is not greater than ISO 4406 (1999) 15/13/10.

• This is no different to that needed for Variable Displacement Piston Pumps which are far more expensive than Servo’s

Catastrophic Failure

‘When a system is assembled and installed, built-in and ingested contamination will cause a particle chain reaction leading to catastrophic failure on initial start-up’

Always work to a planned flushing programme. Qualifying and isolating clean areas to obviate re-contamination!!!!!!!


The Planned Flushing Programme


Programme

• Look at the system as a whole.• Then breakdown the systems into

manageable elements where planned flushing and cleanliness qualification can be made.

• Then introduce the critical parts after ISO verification has been determined obviating re-contamination.


The Three Main Elements

1)The Actuators & Valve Stands

2)The System Pipe-work

3) The Power Unit

.


Goodrich UndercarriageSystems - Toronto

Star’s Service Partner& Distributor


It’s a good practice to review where the filters are located.

The “Workhorse Filter” should be the finest rating and largest in dirt

capacity. It should also be located avoiding as best possible pressure and

flow surges.


Lets discuss:-Filter locations,Filter SizingFilter RatingsBeta Ratio’s Beta StabilityFilter IntegrityDirt CapacityFilter Servicing

Basic Schematic Drawing 1

Supply Fluid.

Main Tank

Qualify Filter Ratings,

Delta P

Flow Rate of

Offline


Typical Servo Systems Filtration

Within the last three years.A major aerospace companyhad a filter sizing problem

the bypasses were open until the oiltemperature reached 30°centigrade


Beta Stability

Many people assume that a filter will remove and retain all contamination that challenges it!

The facts of the matter are much different!Filter locations, the duty and the service of filtershave effects on the filters performance.

How many filters are undersized ??????

Lets consider how particulate is arrested. w


Betamicron® - Benefits Efficient Mesh Pack Design

Support tubeSupport tube

Support meshSupport mesh

Preliminary layerPreliminary layer

SecondSecondglass fibre layerglass fibre layer

FirstFirstglass fibre layerglass fibre layer

Protective layerProtective layer

Support layerSupport layer

External wrap aroundExternal wrap around

End capEnd cap

End capEnd cap

Filter matFilter mat(mesh pack(mesh pack))


Works as a flowdiffuserPrevents

Turbulence between the pleats

Ensures that pleates do not bunch and shut off surface area.

Oil flow

Hydac Element TechnologyHydac Element TechnologyBenefits of the Outer WrapBenefits of the Outer Wrap


The difference between a laboratory test and the working environment

Remember one is a simulation in a laboratory with test dustand the other is a working environment with aggressive dirt


Filter Integrity


Element Fatigue.

Elements that can not Stand the environmentare probably not fit for

Purpose expectedof them.


Filter Servicing


Filter Servicing

Elements need changing when the indicator signals or after a given period in service (Remember – Element Fatigue!!!!!!)Filter Indicators need to be functionally tested annually.By-pass valves need to be tested or replaced annually.Seals need to be replaced during service.


Condition Monitoring• Set a footprint of the system as it operates:-

– Review ISO/NAS cleanliness from at least two locations – Inline samples are best, suggest Supply and Return lines. Bottle Sampling is not the best way!

– Record normal working operational temperature against ambient temperature.

– Qualify water content in PPM or by percentage.– At appropriate times send samples of fluid for

Chemistry analysis and approval.(Oil companies)– Consider Vibration analysis for pumps/motors. Adopt

where appropriate – Bearing wear is a good indicator!


Timing

• This is very much dependant on each system. • Expect the time scale to initially be, short whilst

the footprint is being established.• Time scales will naturally extend as the data is

compiled. The key tasks will also start to vary as knowledge is gained.

• The key is to always undertake the checks when the system is in the middle of its working day.


A Typical Event ChartsAt the Start

Monthly Quarterly Annually

Oil Cleanliness Oil Cleanliness Oil CleanlinessWater Content Water Content Water ContentOil Temp* Oil Temp Oil Temp

Oil Chemistry Oil ChemistryVibration Vibration

•Temp checks - Return Lines and Drain Lines before Coolers

•Tasks in “Bold” are example of times scales after Foot-print established

Long Servo Life with Star’s Sapphire Technology can be gained when customers

keep the oil filteredto a sensible level which Star in conjunction with our customers

they set themselves


Editorial – Chief EngineerBAE Systems


Technical Support

• Star Hydraulic Support Services

Documents

Servo Technology & Research - Engineering Integrity Societye-i-s.org.uk/wp-content/uploads/2013/10/Barry-Towner-Star-Hydraulic… · 2013/bkj This document is copy-right protected