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Global Filtration Technology

The Handbook of Hydraulic Filtration



C ontamination C auses

Most Hydraulic Failures

The experience of designers a nd users

of hydraulic and lub e oil system s hasverified t he following fact : over 75% of

all system failures are a direct result

of contamination!

The cost due to contam ination is

staggering, resulting from:

Loss of production (downtime)

Component replacement costs

Frequent f luid replacement

Costly disposal

Increased overall mainte nance costs

Increased scrap rate

Functions of HydraulicFluid

Contam ination interferes with the four

functions of h ydra ulic fluids:

1. To act as an ene rgy tra nsmission

medium.

2. To lubricate inte rna l moving part s of

components .

3. To act as a heat tran sfer me dium.

4. To seal cleara nce s betwee n m oving

parts .

If any one of these funct ions is

impaired, the hydraulic system will not

perform as designed. The resulting

downtime can easily cost a large ma nu-

facturing plant thousands of dollars

per hour. Hydraulic fluid maintenance

helps prevent or reduce unp lanned

downtime. This is accomplished

through a continuous improvemen t

program that minimizes and removes

contaminants .

C ontaminant Damage

Orifice blockage

Component wear

Formation of rust or other oxidation

Chemical compound format ion

Depletion of additives

Biological growt h

Hydraulic fluid is expected to create a

lubricating film to keep precision parts

separ ate d. Ideally, the film is thick

enough to completely fill the clearancebetween moving parts. This condition

results in low wear rates . When the

wear rat e is kept low enough, a compo-

nent is likely to reach its intended life

expect anc y, which ma y be millions of

pressurization cycles.

Contam inat ion Basic s

2

Fi l t rat ion Fac tProperly sized, installed,

and m aintained hydraulic

filtration plays a key role

in mac hine preventative

maintenance planning.

Fi l t rat ion Fac tThe func tion of a filter is to

clean oil, but the purpose is

to reduce operating costs.

Actual photomicrograph of particulate contamination(Magnified 100x Scale: 1 division =20 microns)



The actual thickness of a lubricating

film depends on fluid viscosity, applied

load, and the relative speed of the two

surfaces. In m any components , mech-

anical loads are t o such an extreme

that they squeeze the lubricant into a

very thin film, less than 1 micromet er

thick. If loads become h igh en ough, the

film will be pun cture d by the sur face

roughness of the two moving parts.

The result contributes to harmful

friction.

Cont aminat ion Basic s

3

Micrometer Scale

Particle s izes are generally measure d

on the m icrometer scale. One m icrom-

eter (or “micron”) is one-millionth of

one m ete r, or 39 millionths of an inch .

The limit of huma n visibility is app rox-

imately 40 micrometers. Keep in mind

that most dam age-causing particles in

hydraulic or lubrication systems are

smaller than 40 micrometers .

Therefore, they are microscopic and

cannot be seen by the un aided eye.

Typical HydraulicComponent Clearances

Microns 0.5

0.5-1

0.5-51-4

1-25

5-4018-63

50-250

130-450

ComponentAnti-friction bearings

Vane pump (vane tip to outer ring)

Gear pump (gear to side plate)

Servo valves (spool to sleeve)

Hydrostatic bearings

Piston pump (piston to bore)

Servo valves flapper wall

Actuators

Servo valves orifice

Relative Sizes of Particles

Inches.0039.0027

.0016

.0010

.0003

.0001

SubstanceGrain of table salt

Human hair

Lower limit of visibilityMilled flour

Red blood cells

Bacteria

Microns100

7040

25

82



The Handbook of Hydraulic

Filtration is intended to

familiarize the user with all

aspects of hydraulic and

lubrication filtration from

the basics to advanced

technology.

It is dedicated as a reference

source with the intent of

clearly and com pletely

presenting the subject m atter

to the user, regardless of the

individual level of expertise.

The selection and proper use

of filtration devices is an

important tool in the battle to

increase production w hile

reducing manufacturing costs.

This Handbook will help the

user make informed decisions

about hydraulic filtration.



Contamination Basics 2

Contamination Types and Sources 4

Fluid Cleanliness Standards 12

Filter Media Types and Ratings 16

Filter Media Selection 20

Filter Element Life 22

Filter Housing Selection 24

Types and Locations of Filters 28

Fluid Analysis 32

Appendix 34

Table of Cont ent s

1

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Parker Hannifin CorporationHydraulic Filter Division 16810 Fulton County Road #2Metamora, OH 43540Phone: (419) 644-4311Fax: (419) 644-6205http://www.parker.com

HTM-3

Printed in USA

Contact Parker’s worldwide serviceand distribution network by calling:

Argentina • +54 (1) 752 4129Australia • +61 (2) 634 7777Austria • +43 (2622) 23501 3Belgium • +32 (2) 762 1800Brazil • +55 (11) 847 1222Canada • 1-800-272-7537China • +86 (21) 6249 9755Czech Republic • +42 (2) 752544Denmark • +45 (43) 541133

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Parker WorldwideSales Offices

Filtration Group TechnicalSales & Service Locations

Finite Filter Division

500 Glaspie StreetOxford, MI 48371Phone: (248) 628-6400Fax: (248) 628-1850

Hydraulic Filter Division16810 Fulton County Road #2Metamora, OH 43540Phone: (419) 644-4311Fax: (419) 644-6205

Process Filter Division1515 W. South StreetP.O. Box 1300Lebanon, IN 46052Phone: (765) 482-3900Fax: (765) 482-8410

Racor Division

3400 Finch RoadP.O. Box 3208Modesto, CA 95353Phone: (800) 344-3286Phone: (209) 521-7860

Fax: (209) 529-3278

Racor Division

Hydrocarbon ProductsRoute #3 Box 9Henryetta, OK 74437Phone: (918) 652-4481Fax: (918) 652-8882

Filter Division U.K.

Churwell ValeShaw Cross Business ParkDewsbury, England WF12 Phone: +44 1924 487000Fax: +44 1924 487060

Filter Division U.K.

UCC ProductsP.O. Box 3Thetford, NorfolkIP24 3RT England

Phone: (44) 1842-754251Fax: +44 1842-753702

Finn Filter Division

Fin-31700Urjala As., FinlandPhone: (358) 3 54 100Fax: (358) 3 54 10100

Parker Hannifin Ind. e CoLtda. Filter Division

Via Anhanguera, Km. 25,305275-000 – São Paulo

– SP, BrazilPhone: +55 (11) 847 1222Fax: +55 (11) 847 1610

Parker Hannifin Asia Pac

Company, LTD

902 Dae Heung Bldg.648-23 Yeoksam-dongKangnam-ku, Seoul,Korea 135-080Phone: 82 2 561 0414Fax: 82 2 556 8187



C ontamination C auses

Most Hydraulic Failures

The experience of designers a nd users

of hydraulic and lub e oil system s hasverified t he following fact : over 75% of

all system failures are a direct result

of contamination!

The cost due to contam ination is

staggering, resulting from:

Loss of production (downtime)

Component replacement costs

Frequent f luid replacement

Costly disposal

Increased overall mainte nance costs

Increased scrap rate

Functions of HydraulicFluid

Contam ination interferes with the four

functions of h ydra ulic fluids:

1. To act as an ene rgy tra nsmission

medium.

2. To lubricate inte rna l moving part s of

components .

3. To act as a heat tran sfer me dium.

4. To seal cleara nce s betwee n m oving

parts .

If any one of these funct ions is

impaired, the hydraulic system will not

perform as designed. The resulting

downtime can easily cost a large ma nu-

facturing plant thousands of dollars

per hour. Hydraulic fluid maintenance

helps prevent or reduce unp lanned

downtime. This is accomplished

through a continuous improvemen t

program that minimizes and removes

contaminants .

C ontaminant Damage

Orifice blockage

Component wear

Formation of rust or other oxidation

Chemical compound format ion

Depletion of additives

Biological growt h

Hydraulic fluid is expected to create a

lubricating film to keep precision parts

separ ate d. Ideally, the film is thick

enough to completely fill the clearancebetween moving parts. This condition

results in low wear rates . When the

wear rat e is kept low enough, a compo-

nent is likely to reach its intended life

expect anc y, which ma y be millions of

pressurization cycles.

Contam inat ion Basic s

2

Fi l t rat ion Fac tProperly sized, installed,

and m aintained hydraulic

filtration plays a key role

in mac hine preventative

maintenance planning.

Fi l t rat ion Fac tThe func tion of a filter is to

clean oil, but the purpose is

to reduce operating costs.

Actual photomicrograph of particulate contamination(Magnified 100x Scale: 1 division =20 microns)



The actual thickness of a lubricating

film depends on fluid viscosity, applied

load, and the relative speed of the two

surfaces. In m any components , mech-

anical loads are t o such an extreme

that they squeeze the lubricant into a

very thin film, less than 1 micromet er

thick. If loads become h igh en ough, the

film will be pun cture d by the sur face

roughness of the two moving parts.

The result contributes to harmful

friction.

Cont aminat ion Basic s

3

Micrometer Scale

Particle s izes are generally measure d

on the m icrometer scale. One m icrom-

eter (or “micron”) is one-millionth of

one m ete r, or 39 millionths of an inch .

The limit of huma n visibility is app rox-

imately 40 micrometers. Keep in mind

that most dam age-causing particles in

hydraulic or lubrication systems are

smaller than 40 micrometers .

Therefore, they are microscopic and

cannot be seen by the un aided eye.

Typical HydraulicComponent Clearances

Microns 0.5

0.5-1

0.5-51-4

1-25

5-4018-63

50-250

130-450

ComponentAnti-friction bearings

Vane pump (vane tip to outer ring)

Gear pump (gear to side plate)

Servo valves (spool to sleeve)

Hydrostatic bearings

Piston pump (piston to bore)

Servo valves flapper wall

Actuators

Servo valves orifice

Relative Sizes of Particles

Inches.0039.0027

.0016

.0010

.0003

.0001

SubstanceGrain of table salt

Human hair

Lower limit of visibilityMilled flour

Red blood cells

Bacteria

Microns100

7040

25

82



Particulate Contamination

Types

Part iculate cont amination is generally

classified as “silt” or “chips.” Silt can

be defined as th e accum ulation of

particles less than 5m over time . Thistype of contamination also causes

system component failure over time.

Chips on the other h and, are part icles

5m+ and can cause immediate

catastrophic failure. Both silt and

chips can be further classified as:

Contam inat ion Ty pes and Sour c es

4

Fi l t rat ion Fac tNew fluid is not necessarily

clean fluid. Typically, new

fluid right out of the drum is

not fit fo r use in hydraulic or

lubrication system s.

Fi l t rat ion Fac tAdditives in hydraulic fluid

are generally less than

1 micron and are unaffected

by standard filtration

methods.

Hard Particles

Silica

Carbon

Metal

Soft Particles

Rubber

Fibers

Micro organism

Flow

1. Particulate

Silt (0-5um) Chips (5um+)

Types of Contamination

2. Water (Free & Dissolved)

3. Air

Silt



Damage

Sources

Built-in during manufacturing and

assembly processes.

Added with ne w fluid.

If not properly flushed, contaminants

from manufacturing and assembly wilbe left in the system.

These contam inants include dust,

welding slag, rubber p art icles from

hoses and seals, sand from castings,

and m etal debris from machine d com

ponen ts. Also, when fluid is initially

added t o the system, contaminat ion is

introduced.

During system operation, contamina-

tion enters through breather caps,

worn seals, and other system openings

System operation also gener ates inte r

nal contamination. This occurs as

component wear debris and chemical

byproducts react with componen t sur-

faces to generate m ore contamination

Cont aminat ion Types and Sour ces

5

Ingested from outside the system

during operation.

Intern ally generated during

operation (see chart below).

Stress raisers causedby particle collisions

A B

C D

A. Three-body

mechanicalinteractions canresult in interference.

B. Two-body wear iscommon in hydrauliccomponents.

C.Hard particles cancreate three-bodywear to generatemore particles.

D.Particle effects canbegin surface wear.

Abrasive Wear—Hard particles

bridging two moving surfaces,

scraping one or both.

Cavitation Wear—Restricted

inlet flow to pump causes fluid

voids that implode causing

shocks that break away critical

surface material.

Fatigue Wear—Particles

bridging a clearance cause

a surface stress riser that

expands into a spall due to

repeated stressing of the

damaged area.

Erosive Wear—Fine particles in

a high speed stream of fluid eat

away a metering edge or critical

surface.

Adhesive Wear—Loss of oil film

allows metal to metal contact

between moving surfaces.

Corrosive Wear—Water or

chemical contamination in the

fluid causes rust or a chemical

reaction that degrades a

surface.

Generated Contamination




6

Fi l t rat ion Fac tSystem C ontamination Warning Signals

• Solenoid burn-out.

• Valve spool decentering,

leakage, “chattering”.

• Pum p failure, loss of

flow, frequent

replacement.

• C ylinder leakage, scoring.

• Increased servo hysteresis.

Fi l t rat ion Fac tMost system ingression

enters a system through the

old-style reservoir breather

caps and the cylinder rod

glands .

Prevention

Use spin-on or dessicant style filter s for reser voir air brea the rs.

Flush all system s before initial start -up.

Specify rod wipers and replace worn actuator seals.

Cap off hoses and m anifolds during hand ling and mainte nance .

Filter all new fluid before it enters the reservoir.

External Contamination Sources

Mobile Equipment 108-1010per minute*

Manufacturing Plants 106-108per minute*

Assembly Facilities 105-106per minute*

* Number of particles greater than 10 microns ingressed

into a system from all sources.

Ingression Rates For Typical Systems



Water Contamination

Types

There is more to proper fluid

mainten ance th an just removing

part iculate ma tte r. Wate r is virtua lly a

universal contam inant, an d just l ike

solid particle contam inants , must be

rem oved from opera ting fluids. Wate r

can be either in a dissolved s tat e or in

a “free ” stat e. Free , or emulsified,

water is defined as the water above th e

satur ation p oint of a spec ific fluid. At

this point, th e fluid cannot d issolve or

hold any more water . Free water is

genera lly noticea ble a s a “milky”

discolorat ion of the fluid.


7

50 PPM 2000 PPM

Typical Saturation Points

Hydraulic Fluid

Lubrication Fluid

Transformer Fluid

300

400

50

.03%

.04%

.005%

Fluid Type PPM %

1000 ppm

(.10%)

300 ppm

(.03%)

Visual Effects Of Water In Oil



Damage

Corrosion of meta l surfaces

Accelerated abrasive wear

Bearing fatigue

Fluid additive breakdown

Viscosity varian ce

Increase in electr ical conduct ivity

Anti-wear a dditives bre ak down in the

presen ce of water and form a cids. The

combination of water, heat an d dissimilar

meta ls encourages galvanic action. Pitted

and corroded m etal surfaces and finishes

result. Further complications occur as

temperature drops and th e f luid has less

ability to hold wate r. As th e freezing point

is reached, ice crystals form, adversely

affecting t otal system function. Operating

functions may also become slowed or

erratic.

Electrical conductivity becomes a pro-

blem when water contamination weakens

the insulating properties of a fluid, thus

decreasing its dielectric kV stren gth.


8

Fi l t rat ion Fac tA simple ‘crackle test’ will

tell you if there is free

w ater in your fluid. Apply a

flame under the container.

If bubbles rise and ‘crackle’

from the point of applied

heat, free water is present

in the fluid.

Fi l t rat ion Fac tHydraulic fluids have the

ability to ‘hold’ more water

as tem perature increases.

A cloudy fluid may bec ome

clearer as a system

heats up.

Typical results of pump wear due to particulate and water contamination



Sources

Worn act uat or seals

Reservoir open ing leakage

Condensation

Heat exchanger leakage

Fluids are constantly exposed to water

and wate r vapor while being handled

and s tored. For instance, outdoor s tor-

age of tanks an d drum s is common.

Wate r m ay settle on t op of fluid con-

tainers and be drawn into the contain-

er during tem peratur e cha nges. Water

may also be introduced when opening

or filling these containers.

Water can e nter a system t hrough wo

cylinder or actuator seals or through

reser voir openings. Conden sation is

also a prime water source. As the flui

cool in a r eser voir or tank, wate r vapo

will condense on the inside surfaces,

causing rust or other corrosion

problems.


9

250

200

150

100

50

0

% Water In Oil0.0025

Effect of water in oil on bearing life (based on 100% life at .01% water in oil.)Reference: ”Machine Design” J uly 86, ”How Dirt And Water Effect Bearing Life” by Timken Bearing Co.

0.01 0.05 0.10 0.15 0.25 0.50

% B e a r i n g L i f e R e m a i n i n g

Effect Of Water In Oil On Bearing Life

0.0025%

0.01%

0.05%

0.10%

0.15%

0.25%

0.50%

=

=

=

=

=

=

=

25 ppm

100 ppm

500 ppm

1000 ppm

1500 ppm

2500 ppm

5000 ppm



Prevention

Excessive wat er c an usually be

removed from a system. The same pre-

venta tive m easures t aken to minimizeparticulate contaminat ion ingression

in a system ca n be a pplied to water

conta mina tion. However, once exces-

sive water is detected, it can usually

be e liminate d by one of the following

methods:

Absorption

This is accomplished by filter elements

that are designed specifically to take

out free wate r. They usually consist of a

laminant-type ma terial that transforms

free water into a gel that is trapped

within th e elemen t. These eleme nts f it

into s tandard fi lter h ousings and are

gener ally used whe n sma ll volumes of

water are involved.

Centrifugation

Separates water from oil by a spinning

motion. This met hod is also only

effect ive with free wat er, but for larger

volumes.

Vacuum Dehydration

Separates wate r from oil through a

vacuu m a nd d rying process. This

me thod is a lso for larger volume s of

water, but is effect ive with both the

free and dissolved states.


10

Fi l t rat ion Fac tFree water is heavier than

oil, thus it will settle to the

bottom of the reservoir

w here much of it can be

easily remo ved by o pening

the drain valve.

Fi l t rat ion Fac tAbsorption f ilter elements

have optimum

performance in low

flow and low viscosity

applications.

Vacuum dehydration system



Air Contamination

Types

Air in a liquid system ca n e xist in

either a dissolved or en trained ( undis-

solved, or free) stat e. Dissolved a ir ma y

not p ose a pr oblem, providing it stays

in solution. When a liquid conta ins

undissolved air, problems can occu r as

it passes through system components .

There can be pressure changes that

compress the air an d produce a large

amount of heat in small air bubbles .

This heat can destroy additives, and

the base fluid itself.

If the amount of dissolved air becomes

high en ough, it will have a ne gative

effect on the amount of work

performed by the system. The work

performed in a hydraulic system relies

on th e fluid being relat ively incom-

pressible, but air redu ces the bulk

modulus of the fluid. This is due t o the

fact that air is up to 20,000 times more

compressible th an a l iquid in which it

is dissolved. When a ir is prese nt , a

pump e nds up doing more work to

compre ss the air, and less useful work

on the system. In this s ituation, the

system is said t o be ‘spon gy’.

Damage

Loss of transmitted power

Reduced pump output

Loss of lubrication

Increased operating temperature

Reservoir fluid foam ing

Chemical reactions

Air in an y form is a p oten tial source of

oxidat ion in liquids. This accelera tes

corrosion of metal parts, particularly

when water is also present. Oxidation

of additives also may occur. Both

processes produce oxides which pro-

mote the format ion of particulates , or

form a sludge in th e liquid. Wear and

interference increases if oxidation

debris is not prevented or removed.

Sources

System leaks

Pump aera t ion

Reservoir fluid tur bulen ce

Prevention

System air bleeds

Flooded suction p ump

Proper reservoir design

Return line diffusers


11



In order to detect or correct problems,

a contam ination reference scale is

used. Particle counting is the m ost

common me thod to der ive cleanliness

level st and ards. Very sen sitive optical

instruments are used to count the

num ber of part icles in various size

ranges. These counts are reported as

the nu mber of particles greate r than a

certain size found in a specified

volum e of fluid.

The ISO 4406 (Int ernat ional Standards

Organization) cleanliness level stan-

dard ha s gained wide acceptance in

most industries today. A widely-used

modified version of this sta nda rd re fer-

ences th e numb er of particles greate r

than 2, 5, and 15 micrometer s* in a

known volume, usually 1 milliliter or

100 milliliters. The num ber of 2+ a nd

5+ m icromete r particles is used as a

refere nce point for “silt” part icles. The

15+ size range indicates the qua ntity

of larger part icles presen t which con-

tribute greatly to possible catastrophic

component failure.

Fluid Cleanl iness St andar ds

12

Fi l t rat ion Fac tKnowing the cleanliness

level of a fluid is the basis

for contamination control

measures.

Fi l t rat ion Fac tThe ISO code index

numbers can never

increase as the particle

sizes increase

(Exam ple: 18 /20 /22 ).

*The ISO codes described here are for the 2, 5, 15 micron format. A 5, 15 micron format which currently meets the ISO standard, maystill be used in some publications (Example: an ISO code of 16/13 would reference particles in the 5 +and 15 +micron ranges only).

An ISO classification of 18/16/13 can be defined as:

Particles>2 microns

Particles>5 microns

Particles>15 microns

ISO CODE 18 / 16 / 13

18

16

13

2+

5+

15+

1,300 - 2,500

320 - 640

40 - 80

Range Number Micron Actual Particle Count Range (per ml)




ISO 16/14/11 fluid (magnification 100x)ISO 21/19/17 fluid (magnification 100x)

ISO 4406 Chart

24

23

22

2120

1918

1716

15

1413

1211

109

8

76

RangeNumber More than Up to and including

Number of particles per ml

80,000

40,000

20,000

10,000

5,000

2,500

1,300

640

320

160

80

40

20

10

5

2.5

1.3

.64

.32

160,000

80,000

40,000

20,000

10,000

5,000

2,500

1,300

640

320

160

80

40

20

10

5

2.5

1.3

.64



Component Cleanliness

Level Requirements

Many manufacturers of hydraulic and

load bearing equipmen t specify theoptimum cleanliness level required for

their components . Subjecting compo-

nent s to f luid with h igher cont amina-

tion levels may result in much shorter

component l ife.

In th e ta ble below, a few component s

and their recommended cleanliness

levels are shown. It is always best to

consult with component ma nufacturers

and obtain th eir written f luid cleanli-

ness level recommendations. This

information is needed in order to

select t he p roper level of filtrat ion.

It m ay also prove u seful for an y

subsequent warranty

claims, as it may draw

the line between nor-

mal use and excessive

or abusive operation.

Fluid Cleanliness Required forTypical Hydraulic Components


14

ISOComponents Code

Servo control valves 16/14/11

Proportional valves 17/15/12

Vane and piston 18/16/13pumps/motors

Directional & pressure 18/16/13control valves

Gear pumps/motors 19/17/14

Flow control valves, 20/18/15cylinders

New unused fluid 20/18/15

Fi l t rat ion Fac tMost machine and

hydraulic component

manufacturers specify a

target ISO cleanliness

level to equipment in

order to achieve optimal

performance standards.

Fi l t rat ion Fac tColor is not a good

indicator of a fluid’s

cleanliness level.




15

Cleanliness Level Correlation Table

23/21/18

22/20/18

22/20/1722/20/16

21/19/16

20/18/15

19/17/14

18/16/13

17/15/12

16/14/12

16/14/11

15/13/1014/12/9

13/11/8

12/10/8

12/10/7

12/10/6

ISO Code >2 Micrometers

Particles/Millilitre

80,000

40,000

40,00040,000

20,000

10,000

5,000

2,500

1,300

640

640

320160

80

40

40

40

>5 Micrometers

20,000

10,000

10,00010,000

5,000

2,500

1,300

640

320

160

160

8040

20

10

10

10

NAS 1638(1964)

Disavowed SAELevel (1963)>15 Micrometers

2,500

2,500

1,300640

640

320

160

80

40

40

20

105

2.5

2.5

1.3

.64

12

–

11–

10

9

8

7

6

–

5

43

2

–

1

–

–

–

––

–

6

5

4

3

–

2

10

–

–

–

–



The fi lter media i s that part of

the element which removes the

contaminant.

Media usually start s out in sheet form,

and is then pleated to expose more sur-

face are a t o the fluid flow. This redu ces

pressure differential while increasing

dirt h olding capa city. In some case s,

the filter media may have multiple

layers an d mesh backing to achieve

certain performance criteria. After

being pleated a nd cut to th e proper

length, the two ends are fastened

togethe r using a special clip, adhesive,

or other seam ing mechanism. The m ostcommon me dia include wire m esh,

cellulose, fiberglass composites, or

other synthe tic mat erials. Filter media

is genera lly classified as eithe r sur face

or depth.

Surface Media

For surface type filter med ia, the fluid

stream basically has a straight through

flow path. Contaminant is captured onthe surface of the element which faces

the fluid flow. Surface type eleme nts

are genera lly mad e from woven wire.

Since th e process used in manufactur-

ing the wire cloth ca n be very accurate-

ly controlled, surface type me dia ha ve a

consistent pore size. This consistent

pore size is the diameter of the largest

hard spherical particle t hat will pass

through the m edia under specified testconditions. However, the build-up of

contaminant on the elemen t surface

will allow the media to capture parti-

cles smaller th an t he pore s ize rat ing.

Likewise, particles that have a smaller

diame ter, but may be longer in length

(such as a fiber s trand) , may pass

downstream of a surface m edia.

Depth Media

For depth type filter media, fluid must

take indirect paths through the materi-

al which makes up the fi lter m edia.Part icles are trappe d in the maze of

openings throughout the m edia.

Because of i ts construction, a depth

type f i lter media h as ma ny pores of

various sizes. Depen ding on the distrib-

ution of pore sizes, this me dia can ha ve

a very high capt ive ra te a t very small

particle sizes.

The nature of f il tration media and the

contaminan t loading process in a fi lter

element explains why some eleme nts

last much longer than others . In gener-

al, filter m edia cont ain m illions of tiny

pores formed by the media fibers. The

pores ha ve a r ange of different sizes

and a re in terconnected throughout the

layer of the media to form a tortuous

path for fluid flow.

Fil t er M edia Ty pes and Rat ings

16

Fi l t rat ion Fac tSurface media can be

cleaned and re-used. An

ultrasonic cleaner is

usually the best m ethod.

Depth m edia typically

cannot be cleaned and

it is not re-usable.

Surface Media

74 m



The two basic depth media types that

are used for f il ter elemen ts are cellu-

lose and fiberglass.

The pores in cellulose me dia tend to

have a broad ran ge of s izes due t o the

irregular size and shape of the fibers.In contrast, fiberglass media consist of

fibers that are very uniform in size and

shape. The f ibers are generally thinne r

than cellulose fibers, and have a uni-

form c ircular cr oss section. The se typi-

cal fiber differences account for the

performance advantage of fiberglass

media. Thinner fibers mean more actu-

al pores in a given space . Furtherm ore,

thinner fibers can be a rranged closertogethe r to p roduce smaller pores for

finer filtrat ion. Dirt holding ca pacity,

as well as filtration efficiency, are

improved a s a result .


17

Flow Direction

Depth Media

General Comparison Of Filter Media

Media Material

DirtHoldingCapacity

Life In aSystem

InitialCost

Fiberglass

Cellulose (paper)

Wire Mesh

High

Moderate

Low

DifferentialPressure

Moderate

High

Low

High

Moderate

Moderate

Moderate

Low

High

CaptureEfficiency

High

Moderate

Low

Typical coarse fiberglass construction (100X)

Typical fine fiberglass construction (100X)



The MultipassTest

The filtration industry

uses th e ISO 4572

“Multip ass Test

Procedure” to evaluate

fil ter eleme nt perfor-

man ce. This procedure

is also recognized by

ANSI* a nd NFPA**.

During the Multipass

Test, fluid is circu lated

through the circuit

under precisely con-

trolled an d monitored

conditions. The differential pressure

across the test e lement is continuously

recorded, as a constant a mount of con-

taminan t is injected upstream of the

element . On-line laser par ticle sensors

determine the contaminant levels

upstream a nd downstream of the te st

element . This performan ce att r ibute

(The Beta Ratio) is determ ined for

several part icle sizes.Three important element performance

charact eris tics are a result of the

Multipass Test:

1. Dirt holding capacity.

2. Pressure different ial of the test fi lter

e lement .

3. Separa tion or filtration efficiency,

expressed as a “Beta Ratio”.

Beta RatioThe Beta Ratio (also known as t he

fil tration ratio) is a me asure of the

part icle capt ure e fficiency of a filter

element . I t is ther efore a pe rforman ce

rating.

As an e xample of how a Beta Ratio is

derived from a Multipass Test. Assume

that 50,000 particles, 10 micrometers

and larger, were counted upstream

(before) of the test filter and 10,000

particles at that sam e size range were

counted downstream ( after) of the te st

filter. The corre sponding Beta Rat io

would equal 5, as seen in th e following

example:


18

Flow MeterDownstreamSample

UpstreamSample

TestFilter

P Gauge

Reservoir

Contaminant

Variable Speed Pump

Multipass Test Fi l t rat ion Fac tFilter media ratings

expressed as a Beta Ratio

indicate a media’s particle

removal efficiency.

Fi l t rat ion Fac tMultipass test results are

very dependent on the

following variables:

• Flow rate

• Terminal pressure

differential

• C ontaminant type

#of particles upstream

#of particles downstream

“x” is at a specific particle size

50,000

10,000=5

Bx=

B10=

* ANSI – American National Standards Institute

** NFPA – National Fluid Power Association



The example would rea d “Beta ten

equal to five.” Now, a Beta Ratio

number alone means very little. It is

a pr eliminar y step to find a filter ’s

part icle capt ure efficiency. This

efficiency, expressed as a perc ent ,

can be found by a s imple equation:

So, in the example, the particular f il ter

test ed was 80% efficient at rem oving 10

micrometer and

larger particles. For

every 5 part icles

introduced to the

filter a t t his size

range, 4 were

trappe d in the f il ter

media. The Beta

Ratio/ E fficiencies

table shows some

common Beta Ratio

numbers and the i r

corresponding

efficiencies.


19

Beta RatioDownstream

ParticlesUpstreamParticles

100,000 >(x) microns

Beta Ratio(x) Efficiency(x)

100,00050,000

100,0005,000

100,0001,333

100,0001,000

100,000500

100,000100

=

=

=

=

=

=

2

20

75

100

200

1000

50.0%

95.0%

98.7%

99.0%

99.5%

99.9%

50,000

5,000

1,333

1,000

500

100

Beta Ratios/EfficienciesBeta Ratio Capture Efficiency

(at a given particle size) (at same particle size)

1.01 1.0%

1.1 9.0%

1.5 33.3%

2.0 50.0%

5.0 80.0%

10.0 90.0%

20.0 95.0%

75.0 98.7%

100 99.0%

200 99.5%

1000 99.9%

Efficiencyx =(1- 1 )100Beta

Efficiency10=(1- 1 )100

=80%



A number of interrelated system

factors combine to determ ine proper

media and filter combinations. To accu-

rately determine which combinat ion isideal for your system all the se factors

need to be accounted for. With the

developmen t of filtrat ion sizing soft-

ware such as inPHorm, this information

can be used to compute the optimal

selection.However, in many instances

the information available may be

limited. In these cases “rules of

thum b”, based on empirical data and

proven examples, are applied to try

and get an init ial s tarting point.

The cha rts on t he following pages

are designed for just those instances.

Be aware th at rules of thumb u til ize

“stan dard ” values whe n looking at com-

ponents, ingressions, and other system

para met ers. Your specific system m ay

or may not fit into this “standa rd”

classification.

One of the more important points of

the cha rts is to emphasize element

efficiency. Note tha t as less efficient

element s are ut ilized, more passes are

required to obtain th e same ISO

clean liness level as a m ore efficient

element . Secondly, the charts indicate

the effect of system pressure on the

requ ired ISO code. As system pressur eincreases, the oil film thickness

between component parts decreases .

This reduction in clearance allows

smaller micron particles to ha ve

harm ful effects .The charts at temp t to

provide flexibility by providing several

possible solutions for each compo-

nent /system pressure combinat ion.

Selection software such as inPHorm

(shown left) can be an e xtremely usefultool in the selection and specification

of th e proper filtrat ion product . With

computer aided selection, the user can

quickly determine the pressure loss

across a given element, and/or housing

combination, within specific operating

param eter s . The t ed ious process of

plotting viscosity at various point s

and ca lcu la t ing a pressure drop is

elimina ted . Additiona lly, select ionsoftware can predic t sys tem per for -

man ce and e lemen t l i fe – ideal for

predic t ive main tenance programs .

Fi l ter M edia Select ion

20

Fi l t rat ion Fac tThere is no direct

correlation between

using a specific media and

attaining a specific ISO

cleanliness classification.

Numerous other variables

should be co nsidered, such

as particulate ingression,

actual flow through filters,

and filter locations.

How to use charts:

1. Choose th e app ropriate c hart for your

system , hydraulic or lubrication.

2. Starting in th e left column, the

componen ts are listed by order of

sensitivity. Find t he most sensitive

componen t used in your system .

3. Following the color ban d to t he right

of the component selected, choose the

pressure range that th e system operates

within. This step is not require d for

lubrication system s.

4. Follow the color ban d to th e right of the

pressure range selected for the suggested

ISO code for t he system

5. To the r ight of the ISO code, in the

same color band, are th e media efficien-

cies required for the corresponding filter

p lacements . Depend ing on the selection

ther e will be one to thr ee opt ions

available.

6. Be sure tha t th e f i lter p laceme nts

recommendation is on the same level

as the m edia efficiency selecte d.



Fi l ter M edia Select ion

Component Type SystemPressure Suggested Media Efficiency Number of MinimumFilterCleanliness Code Betax >200 Filter Placements Placements

2

5

2

2

2

5

10

2

5

2

5

5

10

2

5

10

2

5

5

105

10

5

10

10

20

10

5

10

16/14/12

15/13/11

15/12/10

17/15/13

17/14/12

16/14/11

18/16/14

17/16/14

17/15/13

19/17/15

18/17/14

18/16/13

20/18/16

19/17/15

19/17/14

<1000

1000-3000

>3000

<1000

1000-3000

>3000

<1000

1000-3000

>3000

<1000

1000-3000

>3000

<1000

1000-3000

>3000

Servo Valves

Proportional

Valves

Variable Volume

Pumps

Vane Pumps

Fixed Piston Pumps

Cartridge Valves

Gear Pumps

Flow Controls

Cylinders

1

2

1.5

2

1

1.5

2.5

1

2

1.5

2.5

1

2

0.5

1.5

2.5

1

2

0.5

1.51

2

1.5

2.5

1

2.5

1.5

0.5

1.5

P

P & R

P & O

P & R

P

P & O

P, R & O

P

P & R

P & O

P, R & O

P or R

P & R

O

P or R, & O

P, R & O

P or R

P & R

O

P or R, & OP or R

P & R

P or R, & O

P, R & O

P or R

P, R & O

P or R, & O

O

P or R, & O

Hydraulic Systems

Component Type Suggested Media Efficiency Number of MinimumFilterCleanliness Code Betax>200 Filter Placements* Placements

1.5

1

2

0.5

1.5

2.5

2

2

5

2

5

10

15/13/11

16/14/12

17/15/13

Ball Bearings

Roller Bearings

Journal Bearings

Gear Boxes

P or R, & O

P or R

P & R

0

P or R, & O

P, R & O

Lubrication Systems

21

P = F ull flow pressur e filter ( equalsone fi ltrat ion placemen t)

R = Full flow return filter (e quals onefiltration placement)

O = Off-line ( flow rate 10% of rese r-

voir volume equals .5 of a filtra-t ion placement)

* Numbe r of filtration placem ent s insystem, more placements are theoption of the specifier.



Contaminant Loading

Contam inant loading in a f il ter ele-

me nt is simply the proce ss of blocking

the pores thr oughout the element . Asthe fi lter elem ent b ecomes blocked

with contam inant part icles , ther e are

fewer pores for fluid flow, and the pres-

sure requ ired to m aintain f low through

the media increases. Initially, the dif-

ferential pressure across the element

incre ases very slowly beca use th ere is

an ab undance of media pores for the

fluid to pass th rough, and the pore

blocking process has little effect on the

overall pressure loss. However, a point

is reached at which successive block-

ing of media pore s significant ly

reduces th e num ber of available pores

for flow through the element.

At t his point th e d ifferential pressure

across the element rises exponentially.

The quantity, size, shape and arrange-

men t of the pores th roughout the

element accounts for why some

element s las t longer tha n others .

For a given filter media t hickness and

fil tration rating, there are fewer pores

with cellulose media than fiberglass

media. Accordingly, the contaminant

loading process would block the pores

of the cellulose media eleme nt qu icker

then the identical fiberglass media

element .

The multilayer fiberglass media

element is relatively unaffected by

contaminan t loading for a longer t ime.

The elemen t selectively captures the

various size part icles, as the fluid pass-

es through th e eleme nt. The very small

pores in th e media are n ot blocked by

large particles . These downstream

small pores remain available for the

large qua ntit y of very small part icles

present in the f luid.

Fil t er Element Life

22

D i f f e r e n t i a l P r e s s u

r e

Time

IncrementalLife

Element Contamination Loading Curve

Fi l t rat ion Fac tAs an element loads with

contamination, the

differential pressure will

increase over time; slowly

at first, then very quick ly

as the element nears it’s

maximum life.



Filter Element Life Profile

Every fi lter element has a charact eris-

tic pressure differential versus contam-

inant loading relationship. This rela-tionship can be defined as th e “filter

elem ent life pr ofile.” The ac tua l life

profile is obviously affected by the sys-

tem opera ting conditions. Variat ions in

th e system flow rat e an d fluid viscosity

affect the clean pre ssure different ial

across the f il ter elemen t an d have a

well-defined effect upon the actual

element life profile.

The filter eleme nt life pr ofile is very

difficult to evaluate in actual operating

system s. The system ope rat ing versus

idle t ime, th e duty cycle and t he

changing ambient conta minant condi-

tions all affect th e life pr ofile of th e

fil ter elem ent. In addition, precise

instrument ation for recording the

change in th e pressure loss across the

filter e leme nt is seldom available. Most

machiner y users an d designers s imply

specify filter housings with different ial

pressure indicators to s ignal when t he

fil ter elemen t should be cha nged.

The Multipass Test dat a can be used

to develop the pressure differential

versus contam inant loading relation-

ship, defined as the filter element life

profile. As previously mentioned, such

operating conditions as flow rate and

fluid viscosity affect the life profile for

a filter elem ent . Life profile compar-

isons can only be ma de when these

operating conditions are ident ical and

the f i lter eleme nts are t he same size.

Then, the quantity, size, shape, and

arran gement of the pores in the f il ter

e lement determine the character is t ic

life profile. Filter eleme nts t hat are

man ufactured from ce llulose me dia,

single layer fiberglass media a nd m ul

layer fiberglass med ia all have a very

differe nt life p rofile. The grap hic

comparison of the thre e most commo

me dia configurat ions clearly shows

the life advantage of the multilayer

fiberglass med ia elemen t.

Fil t er Element Life

Element Types Life C om parison

23

00 5 10 15 20 25 30 35 40 45 50

10

20

30

40

50

60

70

80

90 6

5

4

3

2

1

100

CAPACITY (GRAMS)

Cellulose MultilayerFiberglass

Single LayerFiberglass

D I F F E R E N T I A L P R E S S U R E ( P S I )

D I F F E R E N T I A L P R E S S U R E ( b a r )



Filter Housings

The f il ter housing is the pressure vessel

which contains th e f il ter elemen t. I t

usua lly consists of two or more su b-

assemblies, such as a head (or cover)

and a bowl to allow access t o the filter

element . The h ousing has inlet and out -

let ports allowing it to be installed into a

fluid system. Additiona l housing feature s

may include m ounting holes, bypass

valves an d elem ent condition indicators.

The primary concerns in th e housing

selection process include moun ting

meth ods, porting options, indicator

options, and pressure rating. All, except

the pre ssure rating, depen d on the ph ys-

ical system de sign an d the preferences

of the designer . Pressure rating of the

housin g is far less a rbitr ary. This should

be det ermined before th e housing style

is selected.

Pressure Ratings

Location of the f i lter in the circuit is the

primary determinan t of pressure rat ing.

Filter housings are generically

designed for three locations in a cir-

cuit: suction, pressure, or return lines.

One char acte ristic of the se locations is

their m aximum operating pressures .

Suction and return line filters are

genera lly designed for lower p ressures

up to 500 psi (34 bar) . Pressure filter

locations may require ratings from 1500

psi to 6000 psi (103 bar to 414 bar) .

It is essential to analyze the circuit for

frequent pr essure spikes as well as

steady state conditions. Some housings

have rest rictive or lower fatigue

pressure ratings. In circuits with fre-

quent high pressure spikes, another

type housing may be required to

prevent fatigue related failures.

Fi l t er Housing Select ion

24

Fi l t rat ion Fac tAlways use an element

condition indicator w ith

any filter, especially those

that do not have a bypass

valve.

Fi l t rat ion Fac tAn element loading with

contaminant will continue

to increase in pressure

differential until either:

• The element is replaced.

• The bypass valve opens.

• The element fails.

Visual/electrical elementcondition indicator

Bypass valve Assembly

Pressure housing

Filter element

Inlet port

Drain port



The Bypass Valve

The bypass valve is used to pr event t he

collapse or burst of the f il ter eleme nt

when it becomes highly loaded withcontaminan t. I t also prevents pump

cavitation in the case of suction line

filtration. As contaminant builds up in

the element , the differential pressure

across the elemen t increases . At a

pressure well below the failure point

of the filter e leme nt , th e bypass valve

opens, allowing flow to go around t he

element .

Some b ypass valve d esigns ha ve a

“bypass t o-tan k” option. This allows t he

unfiltered bypass flow to return to tank

through a third port, preventing unfil-

tered bypass flow from entering the

system . Oth er filters ma y be sup plied

with a “no bypass” or “blocked”

bypass option. This pre ven ts

any un filtere d flow from going

downstream. In f il ters with no

bypass valves, higher collapse

strength elemen ts may be

requ ired, especia lly in high

pressur e filter s. Applications

for using a “no bypass” option

include se rvo valve an d othe r

sensitive component

prote ction. When specifying a

non-bypass filter de sign, ma ke

sure that t he elemen t has a dif-

ferential pressure rating close

to maximum operat ing pressure of the

system. When specifying a bypass type

filter, it can generally be assumed that

the manufacturer has designed the

element to withstand the bypass valve

differen tial pressure when the bypass

valve opens.

After a housing style and pressure

rating are selected, the bypass valve

setting needs to be chosen. The bypas

valve setting must be selected before

sizing a filter housing. Everything e ls

being equal, the highest bypass

cracking pressure available from the

man ufacturer should be selected. Thi

will provide th e longest ele men t life f

a given filter size. Occasionally, a low

setting may be selected to he lp

minim ize ene rgy loss in a system , or t

reduce back-pressure on another com

ponent. In suction filters, either a 2 o

3 psi (0.14 bar or 0.2 bar) bypass valvis used to minimize the ch ance of

potential pum p cavitation.


25

950 psi(66 bar) 0 psi

(0 bar)

1000 psi(69 bar)1000 psi

(69 bar)

Filter

(ElementsBlocked)

Bypassvalve50 psisetting

(3.4 bar)

Bypass Filter Bloc k edBypass Filter

F l o w

0

2

Beta Performance Lost by Cyclic Flow and Bypass Leakage.

E f f e c t i v e F i l t r a t i o n R a t i o B 1 0

4

6

S t e a d y

F l o w

– N o L

e a k a

g e

U n s t e a d y F

l o w – N o L e a

k a g e

8

10

0 2 4 6 8 10 12

12

U n s t e a d y F l o w

– 1 0 % L e a k a g e

Uns tead y Flo w–20 % Leaka

ge

Uns tead y Flow–40% Leakage

B10 From Multipass Test

BetaLost byCyclicFlow



Element ConditionIndicators

The element condition indicator

signals when the element should be

cleaned or replaced. The indicator usu-

ally has calibration marks which also

indicat es if the filter bypass valve h as

opened. The indicator may be mech an-

ically linked t o th e b ypass valve, or it

may be an entirely indepen dent differ-

ential pr essure sen sing device.

Indicat ors ma y give visual, electrical or

both types of signals. Generally, indica-

tors are set to tr ip anywhere from

5%-25% before th e b ypa ss valve ope ns.

Housing And Element Sizing

The filter housing size should b e large

enough to ach ieve at least a 2:1 ratio

between the bypass valve set t ing and

the pressure differential of the filter

with a clean elemen t installed. I t is

preferable that this ratio be 3:1 or

even higher for longer element life.

For example, the graph on th e next

page illustrates the type of catalog

flow/pressure differe ntial c urves which

are used t o size th e filter housing. As

can be seen , the specifier needs to

know th e ope rat ing viscosity of the

fluid, and the maximum flow rate

(instead of an average) to make sure

that the fi lter does not spend a high

portion of time in bypass due t o flow

surges. This is particular ly importa nt

in return line filters, where flow multi-

plication from cylinders may increase

the re turn f low compare d to the pum p

flow rate .


26

Fi l t rat ion Fac tAlw ays consider low tem-

perature conditions when

sizing filters. Viscosity

increases in the fluid may

cause a considerable

increase in pressure differ-

ential through the filter

assembly.

Fi l t rat ion Fac tPressure differential in a

filter assembly depends

on:

1. Housing and element

size

2. Media grade

3. Fluid viscosity

4. Flow rate

Filter Element Sizing

3:1 OptimumRatio

CleanElement

P

D i f f e r e n t i a l P r e s s u r e

L I F E

FilterBypass

CrackingPressure



If the f il ter described in t he graph was

fitte d with a 50 psi (3.4 bar) bypass

valve the initial (clean) pressure dif-

ferential should be no greater than 25

psi (1.7 bar) and preferably 16 2 ⁄ 3 psi

(1.1 bar) or less. This is calculated from

th e 3:1 and 2:1 rat io of bypass setting

and initial pressure d ifferential .

Most standard filter assemblies utilize

a bypass valve to limit th e ma ximum

pressure drop a cross the f i lter

element . As the f i lter elem ent be comes

blocked with contaminan t, the pre s-

sure different ial increases until the

bypass valve cr acking pre ssure is

reached. At this point, the flow

through t he fi lter assembly begins

bypassing the fi lter element and pa sses

th rough th e bypass valve. This action

limits the maximum pre ssure differen-

tial across the f i lter element . The

important issue is that some of the

system cont aminant particles also

bypass the f il ter eleme nt. When this

happens, the effectiveness of the filter

element is compromised and th e

attainable system fluid cleanliness

degrades. Standard f il ter assemblies

norm ally have a bypass valve cr acking

pressure bet ween 25 and 100 PSI (1.7

and 6.9 bar) .

The relationship between the s ta rting

clean pre ssure differential across the

filter element and the bypass valve

pressure sett ing must be considered.

A cellulose element has a narrow

region of exponential pressure rise.

For this reason, the r elationship

between th e s tarting clean pre ssure

differe ntial an d th e bypass valve

pressure setting is very important. Th

relationship in effect de term ines the

useful life of th e filter eleme nt.

In contra st , the useful element l ife of

the single layer and multilayer fiber-

glass elemen ts is es tablished by the

nea rly horizontal, linear re gion of rel

tively low pressur e drop inc rea se, not

the region of exponent ial pressure r is

Accordingly, the filter assembly bypas

valve cracking pressure, whether 25 o

75 PSI (1.7 or 5.2 bar) , has re latively

little impact on the useful life of the

filter element. Thus, the initial

pressur e differe nt ial and bypass valve

sett ing is less a sizing factor when

fiberglass media is being considered.


27

Typical Flow/Pressure Curves For A Specific Media

0 25 50 75 100 125 150 200 225 250 275 300 325 350 375

0

0.25

0.5

0.75

1.

1.25

1.5

1.75

0

5

10

100 SUS200 SUS15

20

25

100 20 30 40 50 60 70 80 90 100Flow(GPM) (LPM)

( P S I ) D i f f e r e n t i a l P r e s s u r e

( B a

r )

3:1 RATIO

50/3 = 16 2 ⁄ 3 psid (1. 1 bar)

2:1 RATIO

50/2 = 25 psid (1.7 bar)

At 200 sus fluid, the maximum flow

range would be between 42 gpm

and 54 gpm (159 lpm and 204 lpm)



Return Filters

When the pump is a sensitive compo-

nent in a system, a return f il ter may

be the best choice. In most systems,the return filter is the last compo-

nent through which fluid passes

before ente ring the r eservoir.

Therefore, it captures wear debris

from system working component s

and particles entering through worn

cylinder rod sea ls before such

contaminant can e nter th e reservoir

and b e circulate d. Since t his filter is

located immediately upstream from

the reservoir, its pressure ra ting and

cost can be relatively low.

In some cases, cylinders with large

diamet er rods m ay result in “flow

multiplication”. The incr eased r etur n

line flow rate m ay cause th e filter

bypass valve t o open , allowing

unfiltere d flow to pass downstrea m.

This may be an unde sirable conditio

and care should be taken in sizing

the filter.

Both pressure and re turn f i lters can

comm only be found in a d uplex ver-

s ion. I ts most n otable chara cteris tic

is continuous filtration. That is, it is

made with t wo or more f il ter cha m-

bers and includes the nece ssary

valving to allow for continuous,

uninterr upted f il tration. When afil ter elem ent needs servicing, the

duplex valve is shifted, diverting

flow to the opposite filter ch am ber.

The dir ty element ca n the n be

cha nged, while filtered flow

continues to pass thr ough th e f i lter

assembly. The duplex valve typically

is an open cross-over type, which

pre vent s an y flow blockage.

Types & Locat ions of Fi l ter s

29

Cylinder has 2:1

ratio piston areato rod diameter.

Return line filter is sized

for 66 gpm (250 lpm).

Pressure is generally

less than 25 psi (1.7 bar).

33 gpm

(125 lpm)

Return LineFilters

Duplex Filter Asse mb ly



Off-LineFiltration

Also referred to a s recir-

culatin g, kidney loop, orauxiliary filtration, t his

filtrat ion system is tot ally

independ ent of a

machine’s main hydraulic

system . Off-line filtr at ion

consists of a pu mp, filter,

electr ical motor, and the

appropriate hardware

connections. These com-

ponents are installed off-l ine a s a small sub-

system separate from

th e working lines, or include d in a fluid

cooling loop. Fluid is pum ped out of the

reser voir, through t he filter, and back t o

the reservoir in a cont inuous fashion.

With th is “polishin g” effect , off-line fil-

tration is able to maint ain a f luid at a

constant contamination level. As with a

ret urn line filter, this type of system isbest suited to maintain overall c leanli-

ness, but d oes not pr ovide specific com-

pone nt prote ction. An off-line filtrat ion

loop has th e added advantage tha t i t is

relatively easy to ret rofit on an existing

system t hat h as inadequat e f il tration.

Also, th e filter c an b e serviced without

shutting down t he m ain system. Most

system s would ben efit greatly fromhaving a combinat ion of suction, pres-

sure, ret urn , and off-line filter s.

The table to the r ight m ay be

helpful in mak ing a filtrat ion

location dec ision .


30

Fi l t rat ion Fac tRule of thumb:

size the pump flow of an

off-line package at a

minimum of 10% of the

main reservoir volume .

Fi l t rat ion Fac tThe cleanliness level of a

system is directly proportional to the flow rate

over the system filters.

Pump

Off-LineFilter

Optional Cooler

Air breather ExistingHydraulicor LubeSystem

Off -Line Filter

Flow Rate Effect on Off-Line FiltrationPerformance

.01

.1

23/21/18

20/18/1519/17/14

18/16/1316/14/12

15/13/10

For beta rated filters witha minimum rating of beta (10) =75

(Number of partic les >10 micron ingressing per minute)

Source based on Fitch, E.C., Fluid Contamination Control, FES, Inc.,Stillwater, Oklahoma, 1988.

N u m b e r o f p a r t i c l e s u p s t r e a m p e r m i l l i l i t r e g r e a t e r t h a n r e f e r e n c e s i z e

I S O C o r r e l a t i o n

1

10 1 G P M

( 3 . 8 l p

m )

1 0 G P M

( 3 8

l p m )

1 0 0 G P M

( 3 8 0 l p

m )

102

103

103 104 105 106 107 108 109 1010 1011 1012

104

105

106

Ingression rate




31

Comparison of Filter Types and Locations

FILTERLOCATION ADVANTAGES DISADVANTAGES

Suction • Last chance • Must use relatively(Externally protection for the pump. coarse media,and/or largeMounted) housing size, to keep

pressure drop low due topump inlet conditions.

• Cost is relatively high.• Much easier to • Does not protect

service than a downstreamsump strainer. components from pump

wear debris.• May not be suitable for

many variable volumepumps.

• Minimum system protection.

Pressure • Specific component • Housing is relativelyprotection expensive because it

• Contributes to overall must handle full systemsystem cleanliness level. pressure.

• Can use high • Does not catch wearefficiency, fine filtration, debris from downstreamfilter elements. working components.

• Catches wear debris from pump

Return • Catches wear • No protection fromdebris from components, pump generatedand dirt entering contamination.through worn cylinder • Return line flow surges

rod seals before it enters may reduce filterthe reservoir. performance.

• Lower pressure • No direct componentratings result in lower protection.costs. • Relative initial cost

• May be in-line or is low.in-tank for easierinstallation.

Off-Line • Continuous “polishing” of • Relative initial cost is high.the main system hydraulic • Requires additional space.fluid, even if the system is • No direct componentshut down. protection.

• Servicing possible withoutmain system shut down.

• Filters not affected by flowsurges allowing for optimumelement life and performance.

• The discharge line can bedirected to the main systempump to provide superchargingwith clean, conditioned fluid.

• Specific cleanliness levelscan be more accuratelyobtained and maintained.

• Fluid cooling may be easilyincorporated.



Fluid Analysis Methods

Patch Test

Portable Pa rticle Counter

Laboratory Analysis

Fluid analysis is an essential part of

any mainten ance program. Fluid analy-

sis ensures that the f luid conforms to

manufacturer specifications, verifies

the composition of the fluid, and deter-

mines its overall contamination level.

Patch Test

A patch test is nothing more than

a visual ana lysis of a fluid sam ple. Itusually involves taking a fluid sample

and p assing it through a f ine media

“patch”. The patch is then analyzed

under a m icroscope for both color and

content, and compared t o known ISO

standards. By using this comparison,

th e user can get a “go, no-go” estima te

of a system’s cleanliness level.

Anoth er lesser-used de viation of the

patch t est would be the actual count-

ing of the particles seen under the

microscope. These numbers would

then be extrapolated into an ISO

clean liness level.

The ma rgin of err or for both of the se

methods is relatively high due to the

huma n factor.Portable Particle C ounter

Fluid Analy s is

32

Fi l t rat ion Fac tThe only way to k now the

condition of a fluid is

through fluid analysis.

Visual examination is not

an accurate method.

Fi l t rat ion Fac tAny fluid analysis should

always include a particle count and corresponding

ISO code.

Typical test kit



A most p romising developme nt in fluid

analysis is the portable laser particle

counter . Laser par ticle counters arecomparable to full laboratory units in

counting particles down to the 2 +

micron range. Strengths of this recent

technology include accuracy, repeata-

bility, portability, and timeliness. A test

typically takes less than a m inute.

Laser particle counters will generally

give only part icle counts a nd clea nli-

ness classifications. Wate r cont ent ,

viscosity, and spect rome tric ana lysistests would require a full laboratory

analysis.

Laboratory A nalysis

The laborat ory ana lysis is a complet e

look at a fluid sam ple. Most q ualified

Neutralization num ber

Water content

Particle counts

Spectrometric a nalysis (wear

metals and additive analysis

reported in p arts per million,

or ppm)

Trending graphs

Photo m icrograph

Recommendations

In ta king a fluid sample from asystem, care must be t aken to

make sure th at th e f luid sample

is representative of the system.

To accom plish th is, the fluid

container must be cleaned

before ta king the sample and

Association (NFPA) stan dard for

extracting fluid samples from a

reser voir of an ope rat ing hydra ulic

fluid powe r syste m.( NFPA T2.9.1-1972

There is also the American National

Stan dar d m eth od ( ANSI B93.13-1972)

for extracting fluid samples from the

lines of an opera ting hydraulic fluid

power system for pa rticulate conta mi

nation analysis. Either extraction

method is recommended.

In any event, a representative fluid

samp le is th e goal. Sampling valves

should be opened a nd f lushed for at

least fifteen seconds. The clean samp

bottle should be kept closed until the

fluid and valve is ready for sampling.

The system should be a t operat ing tem

peratu re for at least 30 minutes befor

the samp le is taken.

A complet e pr ocedur e follows in

the appendix.

SAMPLING

Fluid Analysis

Portable particle counter

FLUID ANALYSIS REPORT

SAMPLE DATA

COMPANYNAME: XYZCorpor ation

SYSTEM TYPE: Hydraulic System

EQUIPMENT TYPE: LOADER

MACHINE ID: x1111

FILTER ID:

SAMPLE DATE: 06-01-94

HOURS ( o n o il/u n it): 100 / 100

SYSTEM VOLUME: 20 L

FLUID TYPE:

CITGO AW46

ANALYSIS PERFORMED: AI-BSTV4 (W)

AUTOMATIC PARTICLE COUNT SUMMARY

W A R N I N G

CleanlinessCode

Size Counts per ml.

> 2 µ m 353242.0> 5 µm 34434.0

> 10 µm 2342.0 26/22/14> 15 µm 154.0

> 25 µm 17.0> 50 µm 1.0

FREE

WATER

PRESENT

YES

NOX

PARTEST Fluid Analysis Service

Parker Hannifin Corporation

16810 Fulton County Road #2

Metamora, OH 43540

Tele:(4 1 9 )6 4 4 -4 3 1 1

Fa x :(4 1 9 )6 4 4 -6 2 0 5

SAMPLE CODE: 1034 DATE: 06-01-94XYZCorpor ation

12345 Middleton Rd.

Anywhere USA41114

Attn:

30

29

28

27

26

25

24

2322

21

20

19

18

17

16

15

14

13

12

11

10

9

8

7

6

5

4

3

107

5.04.03.0

2.01.5

106

5.04.03.0

2.01.5

105

5.04.03.0

2.01.5

104

5.04.03.0

2.01.5

103

5.04.03.0

2.01.5

102

5.04.03.0

2.01.5

101

5.04.03.0

2.01.5

100

5.04.03.0

2.0

1.5

10-1

5.0

Nu

mber

of

particles

per

ml

>

size

ISO CHART RANGE

CODE

REMARKS

PHOTO ANALYSIS

Mag.: 100x Vol.: 20 ml Scale: 1 div = 20 µm

manual parker

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