Access Flu Seals Pt a Alberta Module Millwright

8/19/2019 Access Flu Seals Pt a Alberta Module Millwright

1/48

1

60301

g

Millwright

Accessories, Fluids

and

Seals

r

Part A

Hydraulics

and Pneumatics

Third Period


2/48

Table

of

Contents

Problerns

Materials

Used

in

Sea1s............

..........5

Metal-to-Metal

Seals.......

................12

Sources of

Contamination............

........................20

How Contamination Levels

are Measured

...........25

How to Read

ISO

Cleanliness

Codes..........

.........27

Target

Cleanliness

Ler.'els

..............28

Construction

of

a

Filter

....................31

Locations

of

Fluid Filters..........

..........................34

Pressure

Lirre

Filters

Retum

Line

Fiiters

..........................36

How Filters are Rated .......................37

How to

Select

a Filter

...........

...........39


3/48

:,.,i{i,',

Accessories, Fluids

and

Seals

-

Part A

Rationale

Why is

it

important

for

you

to learn this

skill?

Hydraulic systems

are

designed to

leak

internally.

and

not to leak

externally. H;,draulic

fluid

is

costl1' and is designed to

be

used

over and over. Leaks

in

hydraulic systems are

an

unnecessary, but

chronic

problem.

Although most

leaks are

minor,

they often

present

a

safeq*

hazard

and

can

lead to catastrophic failure of the

system. For

these

two reasons

it

is

essential

for

you

to know horv to install

and

maintain seals that do not

leak.

Dirt

destroys

h1,'drauiic systems

more

than an-v" other

cause. Hotv well

you

control

contaminatiorr

in

ahydraulic system

deterrnines the

reliabilitl'of

the svsteln. In l-act,

at

least one

major

hydraulics manufacturer doubles

the

u,arranty on their components

if

you

meet

the ISO cleanliness levels generally

accepted

by industry.

To meet

these standards

you

rnust

knor.l' how clear.rliness is

measured and hou'

to select the correct

filters.

A major

pump

failure

generates

considerable

debris.

lt

is

very

impoftant to have

a

filter

located

just

after

the

pump

discharge

to

capture

an.v debris

before it damages components

in

the

rest of the system.

You

must

be sure to flush the system

after

a

catastrophic

faiiure

to ensure that an1'debris

that rnay have

been

forced

past

the filter

is

removed.

Accumulators. reservoirs and fluids are components of

a

hy'draulic system that

you must

understand in order to maintain them. Problems

with

any

of these directly affects the

operation of the system.

Outcome

When

1'ou

have completed

this module

vou

tt'ill

be

oble to:

Describe

accessories, fluids

and

methods of

sealing

these

fluids in hydraulic systeurs.

Objectives

1. Describe

the

characteristics,

applications and

installation

procedures

for

various

seals

used

in

hydraulic

components.

2. Describe

the

methods

used

1o

specif,,particulate fluid

contamination.

3.

Describe the

tvpes, purpose,

application

and rnethods

of specifl,'ing

filters

used

in

hy'draulic

s),stems.

lntrod

uction

In

this

rnodule

vou

leam the

lvpes

of seals to

use in

hy'draulics

and horv

to install

them

so

that they

do

not

leak. You also learn about

the

t-r'pes of reservoirs and accessories that are

ar,'ailable to help

you

get

the most out of

your

h,""draulic system. Bur the

most

impofiant

rnaintenance information

presented

is hou' to keep

the

fluid

in

l

our h,vdraulic

s)'sten.l

clean. This

will

enable

),ou

to

double the u

arran[' titne on son]e colnponents.

Y

Copvrrsht Alberu

AdYanced

Education

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t;

':

Objective

One

llthen

l,ou

ltave

completed

this

objectitte

I'ou

wiil

be

uble

to:

Describe

the

characteristics.

applications

and

installation

procedures

for

various

seals

used

in hydraulic

components.

Problems

with

Leaks

Besides

being

messv.

leaks

at seals

and

connections

are

hazards

to

y'our

safety

and reduce

the reliability

of

the system.

Safety

Problems

when

1,ou

approach

an

area

that

has hydraulic

leaks

you

should

be au,'are

of the

following

four hazards:

slipping. pinhole

leaks,

fluid

contact

ivith

your

skin.

and fire

and

explosions.

Slipping

Hazard

One

function of

a

hydraulic

fluid

is

to

lubricate.

You

can

easily

slip

on leaked

fluid

and

fal1

onto machinery

in

congested

areas.

ln

some

cases

,vou

may

get

off

with

minor

injuries.

but in other

cases

you

can be

seriously injured

or

killed.

Pinhole

Leaks

High-pressure

fluid

that

jets

through

a

pinhole

leak

is usually

not visibie (Figure

1).

Hou'ever,

tliis fine

stream

offluid

at

pressures

around 2000 psi

can

pierce

your

skin

and

enter

your

bloodstream.

This

can lead

to

_qangrene.

aurputation

or death.

NOTE

Never

attempt

to locate

a

pinhole

leak

rvith

your

hand

(Figure

1).

Pinhole

leaks

are often

invi

sible-

.;'

.....''

't

"

-F='

/$fr

,{{,h

,^"i

);-1,

Fisure

1

-

Pinhole

leaks.

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Adlanced

Education


5/48

'l1i:

'

:. :

Fluid

Contact

with

your

Skin

Hydraulic fluids

can be carcinogenic.

There

are

docurnented

cases

of

hydraulic

fluids

that

have caused

skin

cancer.

This

is true for common

hvdrocarbon-based

fluids.

but even

more so for

synthetic fluids.

Fire

and Explosion

Hazards

The commonly

used

hvdrocarbon-based

fluids

are flammable

and can be

ignited

with

a

flame or by

contact

with

objects

at

telnperature

above

250"C. You

should also

be

arvare

that hydrocarbons

can

explode when

they contact pure

oxygen

(e.g.,

from a cutting

torch).

Problems with Reliability

in

a

System

Burst lines

and

seals

and even

pinhole

leaks

can

quickly

cause

the system to

shut down.

but so-called rninor leaks also reduce the reliabiliq'

of

a

system. Contaminants

such

as air

and

dirt

are sucked

into

the system through

leaky

connections and

seals

when the

pressure

drops

at

the

iniets

to

pumps

and actuators.

Tl-Lis

is referred

to

as

ingested

contamination

(Fieure

2).

Work

Hardened

Particles

Ingested

Contaminants

ated

Dirt

Leaky Fitting

Figure

2' Ingested

contaminants.

Abrasive

parlicles

that

get

into

the system

u'i1l

remove

rnetal

frorn the r.r'orking

parts

of

valves. pumps

and actuators.

The metal that is removed

rvork-hardens

and

be

very

ef-fective in removing

more

metal. In

this way.

wear

and

damage

to the

parts

accelerates

until

a

component fails.

NOTE

Dirty

gritry'oil

acts

verl,rvell

as a

grinding

compound.

Copl righL .Albena Adr

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Fducarlon

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Air in the

system is

carried by

the

fluid

into

high-pressure

regions,

where

the

bubbles

collapse

violently

and

remove

metal from

cornponents.

The destruction

of the

component

ploceeds

in

the

sarne

way

as

it

does

with

abrasive

contaminants.

Air

also

causes rapid

wear in

working

parts

because

it

drasticallir

reduces

the

ability

of

the

fluid

to

lubricate.

Abrasive

u,'ear

and

generation

of

heat

will

resuh.

As

you

can

see,

the

minor leaks

cause serious

(costly)

damage

to any hydraulic

system.

Effective

sealing

is

the answer

to

this

problem.

The

aircraft

industry

has

dernonstrated

that

you

can

virtually

elir-ninate

all

leaks

since they have

s1,'stems

that do

not leak. Your

commitment to

effbctive sealing

u'ill

result

in large pay,backs

in tenns

of

uptirne, reduced

maintenance costs

and the

elirnination

of

untimel_v

svstern failures.

Cost

of Lost

Fluid

In most

cases

the

cost

of

fluid lost from

srnall

leaks

goes

unnoticed

since this cost

accumulates

gradually.

However, there

are savings to

be

gained

by eliminating leaks

over

the

course

of

a

year.

The magnitude of this

saving

can

be

seen

from

an

estimate that over

a

hundred

million

gallons

of

fluid

are

lost

in

the

hydraulics

industry

through

leaks

each

vear.

Also-

a

Mobil

Oil

Corporation survel'

found that the

average

plant

used

four

times

the

amount of

h-vdraulic

oil

than its

n-rachines

can hold

On larger leaks, the

cost

is tnore

noticeable. For example. the

seal on

a

large

cvlinder at a

steel

mill r.vas

allowed

to

leak

a

thousand litres

per

eight-hour

shift for a month. The

cost

of the fluid and

cleanup were noticeabie.

Another

source

of

large

leaks that

is not

uncolnmon

is

burst hoses. Many

s1'stems

have

hoses

that

cary

flows

of over

a

hundred

sallons

per

ntinute. When

one of these hoses

bursts. most of

the contents

of the

resert,oir

are

lost

before

the

system is

shut down.

Finding Leaks

Wlren you

look

at a machine that

y,ou

know

has

leaked

(because

you

can

see oil

spread

over numerous pipes.

on

the

sides

of the rnachine,

on

the

u'iring

and on

tire

floor), you

may

be hard

pressed

to

point

to

the

exact

source of the

leak.

Ti-re

following

steps can help

)ou

locate the leak.

r

Clean the

area

as

best

you

can

and rvatch

keenly,'

for

the leak.

r

Focus

on

fittings

first and then

hoses and

seals.

.

Suspect the

fitting

that

is rnost

difficult to

get

at since it

will

have

been tlre

hardest

to tighten properly..

Types

of

Seals

There

are

a

number

of different

t1,pes

of

seals.

Positite

seals are

designed

for zero

leakage. wh1le non-posirn,e

seals

allou'contlolled

leakage.

Two

major ciasses

of

seals

used

in rotary

pumps

are

stalic

and

d.vnantic

seais. Sralic

seals

seal between stationaryr

parts

and

d),namic

seals seal betrveen

moving

parts.

Also.

seals

will

be

made

of

specific

materiais that are compatibie

u'ith

the telnperatures, pressures

and

products

that they''

lrust

seal

asainst.

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Positive

Seals

Any

seal

that

does not

allow

any

leakage

is

classed

as

a positive

seal.

In hydraulics,

you

'"'f

"oil:*}:t};:::ff

"::,

r metal-to-rnetal

joints

on

housings,

e

sealant between

rnetal

surfaces;

:

f:{.;,.ft

":s

on

PiPes'

tubes and hoses'

Non-Positiye

Sea/s

Non-positive seals allou'controlled leakage

for

lubrication.

In

hydraulics,

you

will

find

them

used

between

surfaces

in which

one

surface is rnoving. The foilorving are examples

"t'

i-

ln:#xilff

:il

:,*','il:

"'

motor

agai n

st

the varve

pr

ate'

o

pistons

against

the cylinder walls.

.

gear

teeth

against

the

casing

and

against

each

other at

the

rnesh

point,

:

i:i[::

ll;#:l"t"ffi,i]:;:i:"^o

the drive

shaft

on

pumps

and

motors and

Static

Seals

Static seals

provide

a seal between two surfaces that do

not

move rvith

respect

to each

other. The

seals

listed

as

positive

are exarnples of

tliis

class

of

seal.

Dynamic Seals

Dynamic

seals must seal against

a moving

surface.

ln order to

reduce the heat

and

rvear

from

contact

u'ith

a movinq surface. these seals allow

controlled

leakage

for

iubrication.

The

seals

listed for

tlre non-oositive seals

are dvnarnic seals.

Materials Used in Seals

Seal materials must stand up to the operating conditions to which

they are exposed. These

conditions include

the follorvins:

.

temperature.

.

pressure.

o

chemical action

of

the product

and

.

surface speed and finish

ofthe

moving

surface that it contacts.

Installation of Seals

Many

seals

fail

because

of

improper

installation.

If

you

scratch

a

seal

surface or

nick,

distort

or

wrinkle a

seal.

1'ou

will create a

potential

leak

path.

To elirninate

these

problems

1,'ou

must take the

time

and care

to follow

the

proper

installation

procedures.

Copl'ri

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Stafic

Seals

Most

static seals that

you rvill

install

require

sufficient

clamping pressure

to resist

the

pressure

of

the

fluid that

1,su

are

sealing.

'fhis

clarnping

pressure

is

provided

either by

bolts or by thread engagement

on

fifiings.

M etal

-to-Mefal

Seal

Sudaces

Metal-to-metal

seals are

used in high-pressure

applications in

which

the pressure

is

steady.

The bolts must

be

sufficiently

tight

to

resist any

separation ofthe

seal

surfaces

due

to

fluid

pressure

inside

the

component.

Metal-to-meta1

seal

surfaces

are very rigid and

do

not

seal if they are

scratched,

distorted

or

if

thev have any deposits

such as difi

or

corrosion

on

thern. When

you

assernble

these

surfaces

you

must take

the

following

steps.

l.

lnspect the surfaces for any imperfections and

stone out any burrs or scratches.

2. Thoroughly

u'ash

the housing to

ensure that

there is

no residual

grit

frorn

the

stoning that

could enter

the

working

parts.

3. Assemble

and

snug

up the

bolts

evenly.

4.

Torque

the

bolts to

a

third of

the recommended torque

in

the

recornrnended

sequence.

ln

most

cases,

this

will be in

a star

pattern

on a

circular assembly

and

in a spiral

frorn

the centre

of a

rectangular assembly'

(Pigure

3).

Spiral Pattern

).

Figure

3

-

Tightening

sequence.

Tighten to

two thirds

of

the

specified

torque

and

then to the

full

torque that is

specified in

the

service manual.

NOTE

Alwal's consult

the service manual

when

y,'ou

assemble

a

hydraulic

component and

follow the bolting

procedure

specified.

You

ma1,

find

that the

torque

on

the

sarle sized bolts

used on

differerrt

cotnponents

can

vary

by

150

foot-pounds. In other

cases a thread

adhesive

may be

specified.

Gaskets

Gaskets are

nrade

of

softer

material

than the surfaces that they seal. Their softness allows

them to

conform to

irregularities.

Gaskets are used in

the

follou'ing

situations.

.

Rising and falling internal

pressure

causes the

surfaces to

move

apart

slightl,v

and

corne

together

as

the

pressure

falis.

The

gasket

can

expand

and compress to

maintain

a seal between

the surfaces.

An

erampie

u,ould be

the

gasket

of

the

head end

cover olt

a

piston pulxp

or nrotor

(Figure

4).

Star

Pattern

i

6030i

gn-4.0.doc

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9/48

Compresses

Low Pressure

Gask

High

Pressure

Bolt Pressure

Lifts

Head

Slightly

Allows

\rd

>

t\g t

to

Expand

Figure

4

-

Gasket

sealing under

a changing

load.

They

are used

to seal

between

surfaces made

of lightweight

or

weak

materials

such

as

aluminum

alloys.

Examples include

alloy

housings,

stamped

metal

or

plastic

covers

and

sheet metal

covers.

They

ale used

to

seal

a specific

area of the

surf-ace.

Examples

include

tl.re

seals

between

stack valves

(Figure

5a)

or

between

the

flex

plates

and

support

plates on

a cartridge style

vane

pump (also

shown in Figure

5b).

a)

O-Ring

Gaskets

Lonc

Tie Bolts

b) Balanced

Vane Pump

Gaskets

Rotor with

vdilE>

rearn Rinn

v

.^..*'

:.

.-..

.

4

Figure

5

-

Gaskets

to

seal a specific

area.

Flat

Gaskets

Flat

gaskets

are very versatile

seals. They

are available

in

a

wide

variet.v

of rnaterials

and

designs

to

seal against

a

large

range

ofpressures.

temperatures

and

fluids.

Plate

I

+

Gasket

Drive

End

;

Support

Plate

| ;

Flex

tl

lt

Cop)rigbt

Alberta

Advanced Education


10/48

'.t

8':''.]

aaa,

Although

flat gaskets

are

simple

to

install. you

must observe

the

foilowing

points

to

ensure

a

good

seal.

o

Clean

the surfaces.

'

Ifyou

have

anv

doubt about

the

flatness

ofthe

surfaces.

check

them

u'ith

a

straight

edge.

If it

is

not practical

to make

a

distorted

surface

flat, then

you

must

replace

the defecrive pan.

o

If

you

have

a

gasket

made

of a

hard

material (for

high-pressure

service), you

u,ill

have

to

stone

out any

scratches,

nicks

or

burrs.

'

Set the gasket

in

place.

Most high-pressure

joints

in

hydraulic pumps,

motors

and

valves are

doweled

for alignment

of the

bearing

that they

house.

These

dowels

also

serve

to aiign the

gasket.

.

Bolt

up the,ioint

to

the torque

specified

in the

service manual

and

as described

for metal-to-metal

ioints.

O-Ring

Gaskefs

O-ring

gaskets

are referred to

as

static O-rings

because they

do

not

seal between

moving

parts.

Static O-rinss have

become

popular

in

hydraulics as a

stationary seal instead

of

using

a

gasket

across

the entire

face

ofmating

surfaces.

They consist

ofa

ring

ofsoft

material

seated in

a

groove.

They are

very effective

seals because they

are soft enough to

conform to inaccuracies

in machining.

but can

seal against high

pressures

since

they are

supported

by the

sides of the

groove

in which

they

are seated

(Figure

6). As

a

result,

they

do

not require

as high a

bolt

load

as

a

flat

gasket.

t:

Groove-

O-Ring

(Cross

Section)

Figure

6

-

Static

O-ring

seal.

When

they

are

used

as

stationary

seals. about

10% of

their

diameter must

project

above

the

groove

in u'hich

they

are seated

(Figure

7). This allou,s

for compression

of

the

O-ring

in

order to seal.

Before

Compression

After

Compression

Figure

7

-

O-ring

compression.

O-rings

are

available

in

a

u'ide range

of

materials

to

seal

against various

pressures and

types

of fluid. It is very important

that

1.ou

use O-rings made

of the material

that is

specified

for

the

component and

the application.

Examples

of

some

of the materials

that

you

will find

in

h1'draulic

components

are

as follou,s.

r

Fluorocarbon (Viton)

is

used

for high-pressure

seais between

support

plates

and

flex plates

in

vane pumps

or motors.

\riton

is

resistant

to chemical

reaction

u,ith

rnost

h1'draulic

fl uids.

1Or/o

of Diameter

Copl'ight Alberta

Advanced Education


11/48

Artificial

rubber

(Neoprene)

is

used

for

low-pressure seals between housings

and

cartridges on cartridge-sq'le vane

pumps.

Neoprene

is

a

less expensive, rubber-

like

material

that

is

resistant to

chemical

reaction

with

mineral oil.

PTFE

(Teflon)

is

used

for

backup rings

to

provide

support

for

neoprene

O-rings

in high-pressure applications

(Figure

8).

prgs.gulg€

\Vider Groove

Pressure

Standard

Groove

Figure

8

- Neoprene

O-ring

with

Teflon

backup

ring.

ln Figure

8. tire

hard

'leflon

backup

ring supports

the softer

O-ring

to

prevent

it

frorn

being

ertruded.

Notice

that

the O-ring

groove

is

u'ider to accommodate

both

rings. If

you

notice a

groove that is

wider than

the

O-ring ahvays

install

a backup

rin-e. When

you

replace

O-rings

it

is

very

easy

to

damage

the

groove

and the

new

O-ring

unless

you

observe

the following

points.

1.

Use an

O-ring

pick to

remove

an O-ring

(Figure

9).

Do not

use

a tool

that can

scratch

the

O-ring

seat and

create a

leak

path. Avoid

prying

O-rings out

with

tools like

scribers. screwdrivers or knives.

Never

use a screwdriverl

Damaged

seat

creates

leak

path.

Use

an

Figure 9

-

Use

an

O-ring

pick.

Copvri

ght

Albena Advanced

Educatron

i60-i01gp4.0 doc

i:ifi :.:

-:


12/48

10

.'

2.

Clean

and lubricate

the O-ring

groove

and

the

surfaces

that the

O-ring must

pass

over

to install it.

Tape any

sharp edges

or use

a

sleeve

to avoid cutting

the

O-ring on

these

edges.

Tape

over sharp

edges.

\

Lubricate

O-ring

Figure

10 -

Avoid

cutting

an

O-ring.

Lubricate the

O-ring

with the fluid

to be used

in

the system:

then

carefully

slide

it

into

the

groove.

:

.

I.

NOTE

Do not

twist

the

O-ring

and do not stretch

it

any more than

is

necessary to

get

it to

the

groove.

Sealants

ln hydraulics.

sealants

are used on tapered threads

and betu,een high-pressure

iip

seals

and

the

casing

when the seal is

being replaced.

Sealin

g

Tapered Threads

As

you

can see in Figure 11. there is a clearance

between the

crest and

the root of

the

thread that creates

a

spiral

leak

path.

You

can apply

liquid

PTFE

(Teflon)

to

the male

threads to

seal

this leak

path.

Spiral

clearance

allows leak

Figure 11

-

Spiral

leak

path

in

a

tapered

pipe

thread.

(Courtesy

Eaton Corporation, Hydraulics Operations)

NOTE

When

,vou

apply

sealant

to

a

pipe

thread

,vou

must avoid the first two

threads from

the

end

(see

Figure

12)

to

prevent

sealant

getting

into

the

system. When

sealant

gets

into the

svstem it clogs

pilot

passages.

causes

valve

spools to

stick,

or

prevents poppets

from

seating

properly.

''..

Yr/z

)'.v"1

^\

\\'\

External

I

6030i

$r4.0.doc

Copr

right

.Alhena

.Adr

aneed f

ducarron


13/48

ll

t

In

hydraulics.

you

should apply liquid

sealant to tapered

pipe

threads

instead

ofPTFE

(Teflon)

tape. Bits

of Teflon

tape can

shred and

get

into the bore of

the

pipe

when

1,ou

engage

and tighten the threads.

No sealant on

threads

fitting.

Figure

12

-

How

to

apply

sealant to

pipe

threads.

Sealing High-Pressure Lip

Sea/s

to

the

Casing

When

you

replace

a

high-pressure

lip

seal

you

will find that it

has

a

press fit

into

the

housing. Hou,ever, after

the seal

has

been replaced

a f-erv

times

the

housing

fit

may

not

be

tight

enough to

retain

tire seal securely.

In

order

to

avoid

the

chance

that

the

seal

might

rotate in the

housing during operation

you

rnust

apply

a

hardening

gasket

type

sealant

to

the

housing

before

you

install

the

seal

(Figure

1

3).

Hardening type

sealant on

seal housing

Figure 13

-

Sealing

the

lip

seal

to the

housing.

these two

\'"

I

\

\

wa,

ffi'

'{t"

Dynamic

Seals

Dynamic

seals

must

seal

to a rnoving

surface

with

as little

friction as

possible.

To reduce

friction

and

r.l'ear

as

much

as

possible

the

seals

must exert

a

rninimum

arnount of

pressure

on the surface to be

sealed.

In

hvdraulics. rnost dynarnic

seals

require lubrication.

To

faciiitate lubrication.

d1'namic

seals

allou,controlled

leakage. The surface must

be free of

irregularities

that create

leak

paths.

Coprrght .Alhena

\Jr

anced

Educatron

160301gp4.0

doc


14/48

t:

|.:

';

Metal-to-Metal

Seals

A4etal-to-metal

seals

are

used

to control leakage

between

parts

inside the components. In

pumps

and motors. the

total amount of controlled

leakage through

all

the

rnetal

to metal

seals

is

typically 5Yo to

15%

of the

flow

that

enters

the

component.

Hardened

Sfeel Valve

Plates and

Pressure Plates

These

seals consist of a flat

plate

rvith

ports

cut

in it

that must

seal against the rotor

in

a

vane

pump

or motor.

Figure

l4

shows

that

the seal

surfaces

are spring-loaded as u'ell as

h1'draulically

balanced.

Spring

Pressure

Plate

Pressurized

Fluid

Figure

l4

-

Pressure

plate

seal.

To

ensure that there

is no

leak

path

between

the

ports

you

rnust

lap

these

surfaces

and

polish

them

with

crocus

cloth on

a

flat

surface. This

is normally part

of an overhaul

procedure

that may

be

done in anoti.rer location

than

in

)'our

plant.

You should

inspect

these

surfaces for uneven ll'ear

and

for

score marks or

scratches that fonn

a

leak

path

betra'een

ports.

As

you

can

see.

the seal

surfaces

are

separated

by'a

thin film

ofpressurized fluid

to

provide

lubrication at all times. The spring

pressure

prevents

the

suri'aces

frorn

separating

bey6n6 the

gap necessary for

the

t'ilm of lubricant.

Brass

FIex Plates

and

Wear Plates

Brass

flex

plates

seal against the

rotor

in

a

vane

purxp or motor

ra'hile

brass

rvear

plates

seal against the

gears

in

an extemal

gear pump.

Tliey' seal in the same

\\'ay

as

the valve

plate

and

rotating

group

seals

in a

piston pump

or motor

(Figure

15).

lnspect

the

surfaces

of these

parts

for leak

paths

as

you would

for

the

r,alve

plate

in

a

piston pump

or motor.

Pressurized

Film

of

Fluid

1 6030 1

gp4.0.doc

Copy,ri

ght

Albena

Advanced

Education


15/48

"-,

ii:.

{i

Face

of

Brass Wear

';.#

fr'

--

f

Brass Flex Plate

Face

of Rotor

Figure

15

-

Flex

plates

and

wear

plates.

Shaft

Seals

Shaft seals can

be either high-pressure

lip

seals

or mechanical

seals.

H

i

gh-Press

u

re Li

p

Seals

High-pressure

/rp

seals

are used

to seal against

the

case

pressure

in hydrauiic

pumps

or

motors. The

pressure

in the

case

is rnuch

lower than

the system pressure

and should

not

exceed 150

psi;

otherwise,

the shaft

seal

will

blow out.

Low Pressure

tt

Metal

Retainer

rter

Spring

+tt

High

Pressure

Figure

16

-

High-pressure

lip

seal.

(Courtesy

Eaton

Corporation,

Hvdraulic

Operations)

The

high-pressure

lip

seal

design

contacts

the

shaft

by

means

of

a

very thin

lip

(Figure

16). The garler

spring hotds

the lip

in

contact

u'ith

the

shaft

u.hen

the

purnp

or

motor is

shut down

and the

case

is depressurized.

When

the

pump

or motor

is operating,

the

case

pressures

up and the

case

pressure

acts to

press

the

lip against

the shaft. In

this

way the

seal

is pressure-activated.

But in

order

for

the

lip

to

seal and

not burn out

u'ith

the

friction,

it rnust ride

on

a thin film of

oil.

Therefore.

you

must

al*'ays

prelubricate

the

lip

and the

seal

when

you

replace

a seal.

Copvright

Alberta.Adr,anced

Education


16/48

':':'::'::':'=:

IA

,

IA

..:a.

"

Installation

of

a

High-Pressure

Lip

Seal

A

lip

seal

is very

easiiy

damaged

u'hen

it

is installed

and

if

damaged,

will f-ail

very

quickly,

if

not

irnmediately.

Therefore.

you

must

take

tlre follou.ing

steps

to

ensure

that

the

seal does

not leak.

1 .

c lean

the

bore

in

the

casing

for

the

sear

to relnove

all

burrs

and deposits.

2.

Remove

any

remaining

grit

from

cleaning

and

coat

the

bore

with

hardenine

gasket

t1

pe

sealanr.

3.

Place

the

seal

square with

the casing

bore

and

with

the

open

side

of

the

seal

facing

into

the bore

towards

the

pressure

(Figure

l7).

'j

Use

a

press

Qloorro

Seal

1.

).

Figure

l7

-

Correct

wa1' to install

a

lip

seal.

Select

a

sleeve u,ith

an

outside

diarneter

0.010

inches

srnaller

than

the

bore

diameter

and

use

it

to press

the

seal

into

the

bore.

use a

press

whenever

possible

to install

a seal

(Figure

I7).

Never

hammer

directll

on a seal

without

using

a

sleer

e.

Remove

all deposits

and

burrs

from

the

shaft u,ith

fine

emer1., cloth

and

porish

rl,'ith

crocus

cloth.

NOTS

When

rou

ernerl'the

shaft.

keep

the

strip of errery'at

right

angles

to

the

axis of the

shaft to

ai'oid

creatin-g

spiral

or

longitudinal

scrarches

that provide

ieak paths

through

the

seal

(Figure

I

8).

Open

side

towards

pressure

Copvright

Alberta

Advanced

Ed

ucat'on


17/48

l5

Make

the

marks

circumferential.

Emery

at right angles

to the

shaft.

Figure

l8 -

How

to emery a shaft.

6. Wipe

any'

remaining

grit

from

the

shaft and install

a

thimble. The

purpose

of the

thimble is to

prevent

the lip frorn beirrg darnaged by the edge of the shoulder

(Figure

l9).

Do not

attempt to install

the seal

without protecting

it from

the

edge on the shoulder. It

has

been

proven

that, even after

taking

every other

orecaution.

the seal leaks after

installation

when a

sleeve is

not

used.

Figure

19

-

Use a thimble

to

install

a

lip

seal.

(Courtesy


7.

Lubricate the

seal, the

shaft

and the

thimble

with

the

s,vsteln fluid and

carefully

slide

the

thirnble

and shaft throush the

seal.

Do not use

spiral

marks.

CopYri,ehl Alberta Advanced

Education

l603tl

I

gp4.0.doc


18/48

:tt{

f:6

1 603(t

I

gp-{

t1 l6s

Copvright Alberta

Adlanced

Education

Mechanical

Seals

Figure

20

shows

a

mechanical

seai. This

type

of

seal is

more

elaborate

than

the

lip

seal

and

more expensive.

lt

is

used on

pumps

or motors

that

are designed

to

allow

case

pressures

over 150

psi.

Wave

washer

provides

spring

tension

to force

stationary

face

Housing

against

rotating

face

Shaft

This

part

of seal

remains

stationary

in

housing.

This

part

of

seal

O-rings

provide

static

seal.

Sealing

Surface

rotates with shaft

Figure

20 -

Mechanical

seal for high pressures.

(Courtesy

Eaton

Corporation,

Hydraulics

Operations)

Rod

Sea/s

Figure 21

shows

that the rod

bushing contains

O-rings

on the outside to

prot'ide

a

stationary

seal

to the rod

end head. lnside

the

bushing

)'ou

can

see t$,o

sets of

dy'narnic

seals

that

seal against

the rod. The

seals

that

are

located

torvards

the inside

ofthe c1'linder

are

the high-pressure

seais. They must

seal

against the

load

pressure

on

the

fluid

inside

the cvlinder.

The

pressure

seals

require

support.

so they contain

backup rings.

Backup

rings

are made

of a strong

stiff material

such

as

PTFE,

(Teflon)

to support

the seal ring.

The backup

ring

has

a

small clearance to

the rod. The

seal ring may'be

of

various

designs.

Stationary

O-Ring

Seal

to

Cylinder

Back-Up

Ring for

Seal

High Pressure

Seal(U-Ring)

Figure 21 -

Rod

bushing.

per

Seal

Pressure

Holes to

Activate

U-Ring

Seal


19/48

:-i;''ii::::.;;;

''

, X|

:

ln

Figure

22

aIJ-ring

design

is

used.

Figure

22

also shows five

other

types

of

seals

that

can

be used.

O-Ring

V-Ring

Packing

Back-up Rings for Support

T-Ring

Figure

22 -

T1'pes

of rod

seals.

(Courtesy

Eaton

Corporation,

Hydraulics Operations)

The

seals

located towards the outside

are

r.viper

seals.

These are lip-type seals

and their

job

is to

seal out dirt that is carried on

the

surface

ofthe

rod. The wiper seals

are

very

important. If they fail

and

allow

abrasive

dirt

to be forced under tire

pressure

seals by the

rod.

the

pressure

seals

will

be

damaged. This

u'ill

cause

two serious

and

costly

problems.

First,

the

damaged

seals will

allow

more

dirt

and air into the system during each

intake

cycle

of

the rod

end

of the

cylinder.

Both

air

and

dirt

u'ill

migrate

through

the

entire

system

and

damage all the components. Second,

when the rod

end

is under

conrpressive

load,

fluid

will

discharge

through the

damaged

seals.

When

you

install these seals

you

must take

the

same

precautions that are described

for

the lip

seals.

Dynamic

O-Rings

Dynarnic O-rings

are

used

to seal surfaces

that

move in

a

straight line at iow speed. A

colnnron example

in

h1'draulics is

the

O-ring on

the

spindle to adjust the

pilot

setting

on

a

pressure

control valve

(Figure

23).

a,'::,a

*.ifri'

4

f-..

l-\*

X-Ring

,at

v-1,

ompression

Packing

/t/''

M,

U-Ring

..

%d',

Figure

23

-

Dynamic

O-ring seals.

Copl'right

Alberta Advanced Education

I 6tli0l

gp4.0.doc


20/48

18

1 6L),i0I

gp4.0.doc

Cop\,right

Albena

Advanced Education

The dynamic

O-ring

has

a smoother finish than a

static O-ring to

reduce

wear and

to

minimize lrictional

resistance to movement.

When

you

fit dynamic O-rings

you

will find

that they'operate

with

less

compression

than

static

O-rings

(Figure

24).

Assembled Joint

Distance

'C'

inches Distance'C'

-

0.005 inches

Figure

24

In

cases

where

the

ring

must seal

higher

speeds

(such

as

a

cylinder

suppofi

(Figure 25).

-

Dynamic

O-ring

compression.

against a surface that moves

more frequently

and

at

rod), the

dynamic O-ring

requires

a

backup

ring

for

Pressure

Wider

Groove

Pressure

Standard

Groove

Figure

25 - D1'namic

O-ring and backup ring.

This

backup

ring serves three

purposes.

o

It

allou's

more clearance betrveen

the moving

surfaces to

reduce the

compression

and

friction at

the

O-ring.

r

lt

supports the O-ring

against extrusion

into

the

clearance

betu,een

the surfaces.

r

It acts

as

a *'iper

to

exclude abrasives

from

damaging

the O-ring.

Piston Rings

Piston

seals

are

intemal

seals

that

prevent

or

minirnize

fluid by'passing from one side of

tbe

piston

to the other. Althoughthere are rnany'differentty'pes of

piston

seals. thel'can

be divided into tu'o

general

classes: metallic

and

non-metallic.

R

I

10o/o

of

Diameter


21/48

The

metaliic

piston

seals

have

a

simple rectangular

or square cross-section.

They

are

usually

cast iron,

but can be steel or chrome-plated

steel for harder

wear.

Metaliic

seals

n*

".'n',fi

l""li

x?,?

T#:;'-':"''

.

ttr"y are

compatibte

i,ittr

high temperatures,

o

they withstands

high

pressures and

.

they allow

some leakage.

Because

metallic

seals

allou,some leakage.

they

creep

under

load. lf creep

cannot

be

tolerated

these

seals should not be used. Non-metallic piston

seals

offer many' different

designs. You can

see two of these designs in Figure 26.

Cylinder

Barrel

Cup seals ate

pressure

actuated

Backing

plate

dnd

retainers

clamp cups

tghtly

in

place

A)

Cup Seal

Backup

Ring

T-Ring Seal

B)T-Ring

Seal

Figure 26

-

Non-metallic

piston

seals.

(Courtesl'

Eaton Corporation, Hydraulics

Operations)

Figure

26,4 shou's that

the

cups are

supported

by steel backing

plates;

in Figure

268. the

T-ring

seals are supported

by backup rings.

Copl'right

Alberta

Advanced Educatron

l6030igp4 0.doc

.,IO

....:-

:

:

.::::::

;


22/48

Objective Two

When

ltou

ltave

completed this

objective

you

will

be

able

to:

Describe

the

methods

used

to

specifu

particulate

fluid

contamination.

Since

about 80%

of hydraulic

cornponent failures are

due

to

contamination.

you

can

increase the reliability

of a system significantly

by reducing contarnination

in

the

fluid.

To

do

this

you

must know how

the contamination

gets

into the system. and

how to

lneasure the

amor,rnt

and size of tlre contaminants

in order to knorv u,hat lneasures

to take

to reduce the contarlination

to

an

acceptable

level.

Sources of Contamination

Figure

27

shou's

the four sources

of contarnination.

fittirigs

C)

Ingressed D) Generated

Figure

27

-

Four

sources of

contamination.

There

are

simple.

relatively inexpensive

\\,a_vs

to reduce

contamination

from

each of

these

sources.

-

''.-.--

A) New

Oil

Dirt at rod and

uilt in during assembly

Wear Debris

s

lb0i0l

gp-+.0.doc

Cop),rlght Alberta Advanced Education


23/48

New

Oil

As

you

can

see

frorn

Figure 28 new

new

oil tvoicallv

contains

one and

a

oil

contains considerabie

contamination.

A drum of

haif

billion

particles

of dirt.

Drum Of Clean

Oil

Cylinder

Rod

A major

source

of ingested dirt.

llt

l'

Figure

28 -

Contamination

in new oil.

(Courtesy

Eaton

Corporation,

Hydraulics

Operations)

The

particles

shown in Figure 29

are

rust,

scale.

fibres and

sand.

The

size

of

these

particles

has only been magnified

100

times. Therefore, all of these

particles

can easily

clog

or darnage

components in

a

hydraulic

systern.

v vEot

Surfaces

Figure 29

-

Particles in new oil.

(Courtesy


Abrasive Wear

Copr right .Albena

Adr anced Lducarion

1

60301

gp,l

0

doc


24/48

:::i

i:;ii.r'l

You

cannot

prevent

the contaminants

from getting into

the new

oil,

but

you

can

prevent

these

contaminants

from being

transferred to

the

system. In Figure

30 a

filter

cart is used

to filter

and

transfer the oil to

the

reservoir.

Suction

H

New

Oil

Iter

Hose

eservoir

Filter

Figure 30

-

Filter cart.

The

filter

carl is

simple to make

u'ith readily

available components. You can install

as

t-rne

a fi1ter

as

you

require to meet the cieanliness level that

you

need for

your

s),stem.

,

NOTE ''

in

order to

prevent

a fine

filter frorr

becoming

clogged too

quickly.

install

a

coarse

fi1ter

betu'een the

uurno

and the

fine

filter.

tt

::/:I;l:t,

I 6t)3Ctl

gp4.0.doc

Conln

ght

Alberta A

dvanced

Educatjon


25/48

Besides

removing

contaminants from

new

oil, filter

carls have

other advantages.

.

They make

it easy to transfer

oii with

a

minimum amount

of spillage.

.

They

can be

used

to empty

a

reservoir

for

servicing with

a minirnum

of spillage.

.

They

enable

you

to

pre-filter

the

oil before

start-up. This

is simpll.accomplished

by operating

the filter cart

with both

the

inlet

and

discharge

hoses

in the

reservoir

(Figure

3 1).

Figure

31

-

Pre-filtering

oil

using a

filter cart.

(Courtesl'

Eaton

Corporation, Hl,draulics Operations)

B ui lt-l

n

Contam in

ati

o

n

Built-in

contantinalior'l is contamination that

gets

into

a

component u'hen

it

is

being

assembled.

This

can happen

even in

factory conditions

u,hen

new components

are

being

assembled. The contaminants can include

burrs, chips.

rnoisture. paint,

dust. fibres.

pipe

sealants.

weld splatter

and

flushing

sol_utions. This is

one

major

source of

particles

is

in

pipe

fittings.

When

you

assemble one

'/6

inch

threaded

pipe

fitting

you

introduce

60

000

pal'ticles

into

the svsteln

that are over 5

microns in

size.

This is

one

source that can

be

eliminated

b1'using

ORB

(O-ring

boss)

fittings

to

get

away frorn

abrasive

thread

engagement.

To remove

existing

built-in

contamination,

flush the component u'ith

filtered

oil

before

vou

install

it. Alternativel,v. run the

system and

change

the

return

line fi1ter

after a

tew

hours

ofooeration.

)

Copvright Alhena

Adranceo

Fducatron

J 6030 i

gp4

0

doc


26/48

I

n

g

ressed

Co

nta

m

i n

ati o

n

[rtgressed

contaminanls are

contaminants

that

get

into

a

system from

outside.

Figure 32

shows where contaminants

can enter

the systelr.

Fittings

Leaky

Pump

Seal

Figure

32 -

Entry

points

for

ingressed

contamination.

l-he

following is

a list of measures that

you

can

take

to

reduce ingressed contamination.

o

Filter new

oil as

it is

put

into the s1,sterr.

r

Use a

good

quality

breather cap

with

a

moisture

trap on the reservoir.

r

Change

rod

seals

at the

first

sign

ofleakage

or

preferably

before the

end

oftheir

service

life.

r

Change

purnp

and motor

shaft seals

before

the end of their

service life.

.

KeeP cylinder

rods and

fittings

clean.

Dirt

gets

pulled

into

the

system

at

these

points.

.

Keep

all

fittings tight

and leak-free.

.

Keep the

hl"draulic

system

clean

on the outside

as

u,ell

as

the

surrounding area.

o

Thoroughiy clean

pipejoints

or components and

the

surrounding area

before

you

disassemble these

parts.

Coplright

Alhc'na

.{drrnced Educatron

Dirty

Cylinder Rod

Dirty Fittings

Pouring

Oil

24

i

60301

gp.l

0 doc


27/48

:"i

i.

G

en

erated

Co

n ta

m

i

n

ati

o n

Generctted

contaminatior

is contamination

that is

created

by the

moving

parts

in

a

system.

Table

1 lists

the rval's

in

which

components generate

contaminants.

Type

of

Action

that

Creates

Cont€minants

Cause

Abrasion

Particles

grinding

between

movinq

parts.

Erosion

High-velocity particles

striking

surfaces

Adhesion

Metal-to-metal

contact.

Fatigue

Repeated

stressinq

of a surface.

Cavitation

High

pump

inlet

vacuum.

Corrosion

Foreign

substances

in fluid

(water

or chemical).

Aeration

Gas bubbles

in

fluid, inkoduced from

outside

Table I

-

Contaminant

generating

mechanisms.

How

Contamination

Levels

are Measured

In

order to operate

your

car rvithin

the

speed limits

1'ou

need

a

speedometer

to

measure

the

speed. You must

be able

to

measure

the contarnination

level in

your

hydraulic

system

in

order

to

operate

it

ri'ithin

acceptable

limits

of contarnination.

Contamination

is measured

by'particie

size and

the

number

of

parlicles

of a

particular

size

or

sizes.

How

the

Size of the Particle

is

Specified

The

size

of contarninant

panicles

is rneasured

inmicron.s.Its

sl,rnbol is

p.

A

micron

(also

called

a micrometre)

is

t-rne rnillionth

of a metre in

size.

Since

this unit is used

in

filter

specifications

as

u'eil

as

in target

cleanliness

levels.

1'ou

should have

some

concept

of the

actual

size of a micron.

Figure

33

gives

you

an idea

of

the

size of

particles

that

you

wili

be

concemed

about in contamination

controi.

Grain of Salt 100 Microns

Limit of Visibility

40

Microns

Figure

33

-

Relative

size

of

particles

Smaller

than

Smaller than

a Size of

a white

blood

red blood

cell

bacteria

cell

15

microns

5

microns

2 microns

measured

in microns.

C opr r1g[1 A lben3

.qd\

anccd

tducarron

i

60301 gp-l

0.doc

25


28/48

i,

26'

As

a

millwright you

will

be

famiiiar

with inch

dimensions

expressed in thousandths

of

an

inch. For

example, when you

handle

a

0.001 inch shirn

it

feels

like a

piece

of thin foil.

A

micron

would

be

about 25 times

thinner.

The

particle

sizes that

are

particuiarly

harrnful

to hydraulic

components are

frorn 5

microns

to

15

microns in

size.

Therefore.

the

ISO

cleanliness

codes

specify tlre number

of

particles

of 15 microns and

5

microns.

At

least

one

major

hydraulics

manufacturer

has

added 2-micron

particles

to their

specifications.

This

code has

been

certihed

by the

National

lnstitute

of

Standards and

Technology (NIST)

and

wiil

be adopted

under ISO

4406

(FDIS)

standards. Although

2-micron

particles

cause very

little

wear,

they

are

a

concern because

the

particles

cause

parts

to

stick

when

they

accumulate

in

the

clearance

between

moving

parts.

This is of

particular

concern

in servo valves that have

very close

spool clearances.

NOTE

Notice

that the 15. 5 and

2

micron

particle

sizes

that

do

most of the

damage

in

a

hydraulic

system are

well belou,the

limit

of

visibility

(Figure

33).

Therefore, the

fluid

may

look

clean, but the

contamination

can be unacceptably

high.

How

the Number

of Particles

is

Specified

The

number

of

particles

is specdied

by ISO

standards

by

arange code

(Table

2).

If

you

look

at range

2A

you

will

see

(on

the left

of

the

chart)

that it

specifies

a

range

of

5000 to

10

000

particles

in a one-millilitre

sarnple.

These parlicles

are

counted

electronically under

conditions

that

have been standardized

by

ISO.

Portable

particle

counters are available

and major h1'draulic shops

offer

onsite

testin-q of

fluid

to

determine

the

contamination level. The

particle

counter is

set

to count

2,

5

and

15

micron

particles

and

provides

a

printout

that gives the

range

code

for

each

of

these

sizes.

i{.0301gp4 0 doc

Copyright

Alberta Advanced

Education


29/48

t

L

=

=

;-

o-

{)

,N

a

c

d

-c.

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$

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a

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(U

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z

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:5

2A

Parlicle

siz€

in

mic.orE ers

,lN

4:i 50

20t14112

Cleanliness Code

Table 2 -

ISO

cleanliness

code

chart.

(Courtesl'

Eaton Corporationo Hydraulics

Operations)

How to

Read

ISO

Cleanliness Codes

An example of the

printout

from

a

parlicle

counter

could be 18116 13. When

you

read this

code. the number on

the 1eft

(18)

is

the

range code

ofthe

nuurber

ofparlicles

greater

than

2 microns in a 1-millilitre sample.

The

middle

number

(16)

is the range code

for

particles

greater

than

5

microns

and

the

number

on

the right

(

1

3

)

is for

particles greater

than 1

5

rnicrons.

Copl'right Alberta Advanced

Educadon

l6030lgp4

O.doc

2t


30/48

is'

Target

Cleanliness

Levels

Target

cleanliness

levels

are set

by the hydraulics

industry

to

tell

you

at

what level

the

fluid in

a

hydraulic

system is

too dirry.

They

are expressed

as an ISO

cleanliness

code

(explained

in

the

previous

topic).

Table

2 is

a chart

of these

target

cleanliness

levels.

Table

3

-

Recommended

cleanliness

levels.

(Courtesy

Eaton

Corporation,

Hydraulics

Operations)

I 6(rJOt

gp4

0.doc

Copvr

ght

Alberta

Advanced

Educarion

Pressure


31/48

t The cleanliness

levels

that

are recommended

in

the

chart are for

a

system

that

uses

petroleum

oil for

fluid, runs

continuousiy

and is not

critical

to the

process

operation.

How

to

Sef

a Target

Different

sJ-stems

have

different

requirements

for

cleanliness,

depending

on the

type

of

service

and the

t1'pe

of

components.

You can

set

yourtarget

cleanliness

level

to increase

the life

and reliabiliqv

of

your

hydrauiic

system

by referring

to

the following

steps.

1. From

the Recontmended

Cleqnliness

Code Chart

select

the cleanliness

code

for

the component

in

your

hydraulic

system

that requires

the

highest level

of

cleanliness. The

highest

cleanliness

level is indicated

by the code

with the

lowest

number.

For

example, if

vour

system

operates at

pressures

below 2000 psi.

you

u,ould look

in

the

chart in the


32/48

:.

i.

".

3n:

: :::::::::::::::::::::;J: :t".

:,iil

How

to

Confirm

the

Achievement

of a Target

Now

that portable

particle

counters

are readily

available

either

to

purchase

as

part

of

your

shop

equipment

or through

on-site service

from

a hydraulics

service

shop,

you

can

quickly

have

the

system fluid

sampled

and tested

(Figure

34).

ISO

Range Numbers

Figure 34 -

Portable particle

counter.

Bailer

Probe to

Vickers Target-Pro

Sample: NAITN 102

Date: 04106/01

Time: 02:36:16

Sample

Volume:

30ML

Flow Rate:

S0MLlMin

MIN Max

AVG

2u

2108 2184

2147

5u

451

5A7

472

10u

107

115 109

15u 41

42

41

25u9119

50u010

I 60i01

gp4.0.doc

Copr rig6l Albena

.Adranced

EdLr;auon


33/48

.}

Objective

Three

PI/hen

you

have

completed

this objective you

will

be able

to:

Describe

the

g'pes.

purpose.

application

and methods

of specif

ing filters

used

in

hydraulic

s)'stems.

Construction

of a

Filter

You u'il1

hear the Iern)s

strainer

and/ilter

used and may

run into

some controversy

as

to

the difference

beni'een

the trvo. To

distinguish a

strainer from

a filter,

use

the guideline

that a strainer

is

usually

a

u-ire

mesh with

pore

sizes larger

than

50

microns.

Strainers

are

designed to reriove

coarse contaminants

while filters

are intended

to remove

fine

contaminants.

In

hydraulics,

filters

consist

of

a

metal

case

containing

a filter

element to trap

dir1.

They

also contain

a

bypass valve to

protect

the

elernent

from

collapse when the

pressure

drop

across

the

filter

gets

too

high

(Figure

35).

lndicator rotates showing:

Green

for clean element

Yellow for

partial

bypass

Red for complete bypassing

Air Ble_ed

Passage

Outlet

Check valve close

when

element is ciean.

lnl^+

lt ltEL

Figure

35

-

A

hvdraulic

filter.

(Courtesy'

Eaton

Corporation, H.vdraulics

Operations)

A b1'pass indicator

tells

1'ou

u,hen

the filter

is

operating

on

b1,'pass

(Figure

35).

r-a

a-------l

r


34/48

Filter

Element

In

a

strainer a simple

rvire

screen is

wire

screen

offers the

least

amount

Another

feature

of a

strainer is

that

used to

capture

coarse

contaminants

(Figure

36).

The

ofresistance

to flou'and

has

accurately

sized pores.

it

can be

q'ashed

and reused.

Figure

36

-

Strainer

used on a

pump inlet.

(Courtesy

Eaton

Corporationo

Hydraulics

Operations)

The most

popular

design for

the

filter

element

in hydraulic filters

is

a

pleated

fibreglass

cloth supported by

a

metallic mesh

(Figure

37).

Metallic Suppoft

Mesh

Diffuser Layer

Filter

Media

Diffuser Layer

Metallic Support

Mesh

Figure

37 -

Filter

element.

(Courtesy

Eaton

Corporation,

Hydraulics

Operations)

ln

connection

with

fi1ter

media

you

may hear

the

rerm

deprh

fi,pe

media. Depth

g,pe

media

(Figure

38) consist

of a matrix

of fibres that

capture

dirt as fluid

passes

through.

Fntrannce{

,Particle

\.

\Fibre

Matrix

Figure

38 -

Depth

tlpe filter

media.

(Courtesy

Eaton

Corporation, Hydraulics

Operations)

iX:..

5Z::

I 60J0

I

gp-4

0

doc

Copr right Albena

Adranced Fducarron


35/48

li::

Although

depth

qvpe

filter

media does not

have

a

constant

pore

size, it

is

very

effective in

capturing

dirt.

This

media captures dirt

particles

by forcing the flow

througl-r

a

tortuous

path

and har

ing

manv

areas

in u'hich

dirt

becomes trapped. Depth type hydraulic

filters

are

not u'ashable.

and

rnust

be

discarded after use. Fibreglass

is

superior to paper

because

the

glass

fibres can

be

produced

rrrnch more

frnely

than

paper

fibres,

the1,

can

be laid

rnuch more

uniforulv

and

thel'resist

the chemical action

of

tlre

fluid.

The support

mesh shou

n

in Figure 37 is very important to

the operation of the

filter.

It

must be strong enoush to

prevent

the

pleats

frorn

buckling

and

collapsing

at

the line

pressures.

The

n-resh

also offers some extra filtration.

Bypass

Valve

The

bypass ralte

is a spring-loaded check

valve

that

opens

as the filter

becomes

clogged.

The

valve

is

opened

by

the increased

pressure

drop

(usually

about

45

psi)

as

the

resistance

to

flow of the clogged

tllter increases

(Figure

39). This

allows f'luid to flow

fi'eely

through the centre

of the

filter,

protecting

tlie element

from collapsing or

rupturing.

Indicator

rotates showing:

Green for clean element

Yellow

for

partial

bypass

Red

for complete

bypassing

Bypass

Check

Symbol

Bypass check

valve

closed

when element

is

clean.

Filter Element

Filter

Air Blged

Passage

Outlet

Air

Bleled

Passage

Indicator rotates

showing:

Green

for clean element

Yellow

for

partial

bypass

Red

for

complete bypassing

mr

V

Bypass

Check

Synrbol

Bypass

check valve opens

to bypass

if

element becomes

ctoseo.

Figure 39

-

Operation of the

by'pass

in

a

filter.

(Courtesl'

Eaton

Corporation, Hvdraulics

Operations)

v

Copvright Aiberta

Advanced

Education

160301gp4.0

doc

'::-'


36/48

,,

54'.

:.t'

:a

NOTE

A

pressure

drop of over

45 psi

is hard

on the

filter

elernent and wastes

power.

For

erample,

a

pressure

drop

of 85

psi

at 20

GPM

will

consume

t

horsepower.

Bypass Indicators

Hydraulic filter

manufacturers

strongll' recomrnend

that

you

include

a

bypass indicator.

sometimes called

a

filter condition monitor.

The fype shown in Figure

,10

has

different

coloured

stripes

to

indicate

u'hetherthe

bypass valve is opening

ornot.

Greer.r

indicates

that the full flow is

passing

through the filter element. Yellow

indicates that the by'pass

valve

is beginning to open and the

filter

is

starting to clog, Red indicates that the

filter is

clogged, causing

the valve to be fully open.

Bypass indicator rotates

showing:

Green

for clean

element

Yellow for

partial

bypass

Red

for complete bypassing

Passage

f--{

}------1

L/.\ |

-\iZ-

Bypass

Symbol

Check

valve close

when element

is

clean.

Figure

40 - Bypass

indicator.

(Courtesy

Eaton Corporation,

Hydraulics Operations)

You

should alu'ays change the fi1ter when the

indicator

tums

yellow

to

minirnize the

amount of unfiltered oil circulating through the system.

Another u'ay

to monitor the condition

of the filter is to use

a

gauge

at

the inlet and outlet

ofthe filter

so that

you

can

see the difference

in

pressure

across the

filter.

This pressure

differential is

sometimes called

psid

or

AP.

Psid and

a

differential

pressure

indicator on a

filter should be checked

at operating temperature

The bypass

is also important to ensure

full

flow during cold start-ups

u'hen the

oil does

not flow easily.

Locations

of Fluid Filters

Filters

should

be installed at the

pump

inlet. sometimes in the

pressure line and a1u'ays in

the

return

line

(Figure

41).

In additionto

these locations a

filter

is sornetimes

installed

off-1ine.

Filier

Element

I

60i01

gp4.0.doc

Copl'right

Alberta Advanced Education


37/48

'rt

Return

Line

Filter

Figure 41 - Fluid

filter locations.

(Courtesy

Eaton Corporation,

Hydraulics

Operations)

Pump

Inlets

,

The

pump

inlet requires

a

strainer to rernove

any coarse

contarninants

that might

cause

catastrophic

failure.

A iO0-mesh

filter is

nonlally

used

to

trap

particles

larger

than

150

microns.

Requirements

The main requirement of the

inlet

strainer

is

that

it

passes

the

full

inlet

flou,within

the

pressure

drop

permitted

for that

pump.

If the

pressure

drop is

too high

the iniet flow is

reduced

and

cavitation occurs.

On

in-line

axial

piston pumps.

the

shoes separate

from

the

pistons,

resulting

in catastrophic

failure

if the inlet

flow is insufficient

and

a

vacuum

is

created

in the

oump.

The

strainer

must also

be equipped

with

a

bypass.

This

is to ensure

full flou'when

the

strainer

becomes

clogged

or durins

cold

starts

when

the

oil

is

thick

and u,ill

not

flow

easily.

Pressure

Line

Filters

Pressure

line.filters

are

used

in

the

pressure

line imnrediately

after

the

pump (Figure

38).

These filters

are intended to

protect

the

system components from

contamination

generated

by

the

pump.

You

must always

use a

pressure

line

filter

at

each

servo valve.

Requirements

Pressure

line

filters

must

be capabie

of trapping

fine contaminants.

Thel'

must

also

be

able to u'ithstand

the

operating

pressure

of

the

s1'stem

as well

as

the load pulsations.

These

filters

are

often

specified

u'ith no

b1''pass valve

since

it

is irnportant

not to

b1,'pass

any, contamination

into

erpensive

valves.

v

Copvright

Alberta Advanced

Educatjon

1 6ft l0l on-I

O

rlnn


38/48

Return

Line

Filters

A return

line

filter

is intended

to

control

the contamination

in

the entire

system.

lt

does

this

if

at least20oh

of the

total

system

volume

passes

through

the

filter

per

minute.

Most

industrial

hydraulic

systems

require

a retum

line

filter

to

trap

very small particles

and

protect

high

performance components.

Requirements

and

Types

The return

line

filter

must be

able to handle

the maximurn

return

line

flow with

a

minimum

pressure

drop. This

flow

can be

greater

than the pump

flow

when

a

cylinder

retracts

and discharges

its cap

end flow

back to

tank. For

this

reason

it is important

to

size

this

filter

large

enough

to handle

the

flow

so

that

it

does not

rupture and

allow larse

amounts

of

contaminants

back into

the svstem.

The

return line

filter

is required

to be afull

flow

filler. The

ternfull

flow

means

that the

full

flow

generated

by the system

passes

through the filter

element.

However,

a

return

line filter

u,ill

be

equipped with

a

bypass valve

that is

pre-set

to divert flow

past

the fiiter

element when

the

pressure

drop

gets

above the

setting of the vah,e. This

protects

the

element

from

excessive

Dressure

that

could

collaose

it.

Off-Line Filters

Figure 42

shows two styles

of off-linefihers.In

Figure

42b

permanent

off-line

system

is

being used. In Figure 42a.

apoftable

unit is being

used. The advantage

of the

porlable

unit

is that

it

can be used to

fill or empfv

a

reservoir

at anv

location.

na Prrmn

Portable

Off-Line

Filter

System

Permanent

Off-Line

Filter

System

(a)

(b)

Figure

,12

-

Off-line

filter

systems.

(Cou

rtesy Eaton

Corporation, H.r'drau lics

Operations)

The

off-line filter

pump

is kept

running

continuousiy

to circuiate the fluid frorr

the

reservoir through

the filter. The

size of the

pump

and

the fineness

of the

filter

can

be

selected to achieve

the

target

cleanliness that

-vou

require.

ofr-Li

Circulating

lnlet Stiainer

:::i:::] n

:,t|3,6

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