The Systemic Approach to Contamination Control

Vickers Guide to
Systemic Contamination Control
Contents
2
Vickers Systemic Contamination Control
3
The Systemic Approach to Contamination Control
3
Quantifying Fluid Cleanliness
5
Sources of Contamination
8
Damage Caused by Contamination
16
Setting a Target Cleanliness Level
18
Achieving Target Cleanliness
22
Locating Contamination Control Devices
27
Flushing New or Rebuilt Systems
29
Confirming and Monitoring Achievement of
Target Cleanliness
31
ProActive Maintenance
Vickers Systemic Contamination Control
Fluid Power is one of the most reliable
and repeatable forms of power and
motion control. All that is required is
comprehensive state-of-the-art system
design and modern systemic contamination control. When problems are
encountered, 80% of the time they are
related to inadequate contamination
control practices. Understanding this
handbook will greatly assist the design
or maintenance engineer in achieving
the balanced system cleanliness that is
the cornerstone of fluid power reliability.
Vickers has a more than 75-year
history of dedication to helping engineers
develop, operate and maintain reliable,
high quality power and motion control
systems. This guide is only part of the
package Vickers offers to enable the
designer and user to achieve the
most effective hydraulic power and
motion control.
*systemic (sĭ-stĕm'
˘ ˘ ˘i k) adj.
1. Of or pertaining to a system or
systems.
(American Heritage Dictionary, Houghton
Mifflin Company.)
2
Introduction
For a hydraulic or oil lubricated
machine, the development of a target
cleanliness level and the plan to achieve
it is as much a part of system design
as the selection of the pump, valves,
actuators or bearings. Unfortunately,
when some system designers select a
filter, they look no further than a filter
manufacturer’s catalog, with little regard
for the particular system’s total requirements. Proper selection and placement
of contamination control devices in a
system to attain the targeted cleanliness
eliminates (the root cause of) up to 80%
of hydraulic system failures. Additionally,
the system cleanliness approach assures
the user of the hydraulic system a costeffective approach to contamination
control that allows the price of the filters
and elements to be quickly recovered by
the savings of improved performance,
increased component life, increased oil
life, increased uptime and fewer repairs.
To stress the interacting relationship
between component design, system
design, filter performance and filter
placement, Vickers has named our
approach to filters and filtration Vickers
Systemic* Contamination Control. This
book is dedicated to defining the theory
and practice of quality, cost-effective
systemic contamination control.
The Systemic Approach To Contamination Control
Working toward the most effective
protection consistent with economy, we
must first define our goal. In systemic
contamination control the goal is always
the same: to clean the fluid to the point
that contamination is not a factor in the
failure (catastrophic, intermittent, or
degradation) of any component in the
system during the desired useful life of
that system. The first step towards this
goal is the setting of a target cleanliness
level that takes into account the specific
needs of the system.
Once the target has been set, the next
step is to select and position filters in
the system so that the target can be
achieved in a cost effective manner.
This requires an understanding of filter
performance, circuit dynamics and
filter placement. While all three factors
are important, the last two issues —
circuit dynamics and filter placement —
often receive much less attention than
they require.
Today there are several sources for high
efficiency filters that can initially keep
the hydraulic or lubrication fluids clean.
In most systems that have contamination problems, the cause is either poorly
conceived filter placement, because of
a lack of understanding of the dynamics
of fluid flow, or the inability of the filter
elements to maintain their performance
levels throughout their service life in
the system. The engineering guidelines
needed to deal with both filter placement
and system dynamics are presented in
this document.
After the machine is in operation, the
last and ongoing step is to confirm that
the target cleanliness level is being
maintained. This is most often accom-
plished by sending a fluid sample to a
particle counting laboratory that gives
cleanliness code data to established
standards. If the target is being met,
the system only needs to have filters
maintained and the fluid retested
periodically. If the cleanliness target is
not being achieved, corrective actions
need to be taken. Sometimes a change
in maintenance practices is needed, but
at other times a shift to a finer grade of
filter elements or additional filter housings
may be needed. Intelligent consideration
of contamination control during the
design phase is the best way to avoid
both short- and long-term problems and
gain the assurance that each hydraulically
powered or oil lubricated machine will
give long, reliable service.
Vickers Systemic Approach to
Contamination Control
• Set a target Cleanliness Level
• Select filters and filter placements
to achieve target
• Sample fluid and confirm
achievement
Quantifying Fluid
Cleanliness
The first step in setting a target
cleanliness level is to understand that
“cleanliness” is not a general term but
rather a specific quantitative value.
The current international standard for
cleanliness of a hydraulic or lubricating
fluid is defined by ISO 4406. Using an
approved laboratory particle counting
procedure, the number and size (in
micrometers) of solid particles in a
milliliter of fluid is determined.
Automatic Particle Counting
Light
source
Photodetector
screen
Typical data from a hydraulic fluid
sample counted by an automatic particle
counter is:
Particles Size ‘X’
in Micrometers
Number of particles
greater than ‘X’ size
in one ml of test fluid
2µm
5µm
10µm
15µm
25µm
50µm
5120
89
43
22
3
.4
(Note: Particle counts are normally run on 10 to 100 milliliters of
fluid and then factored to report results for 1 milliliter. This is the
reason results of fractional particles can be reported.)
Computer "reads"
and classifies the
particles by the
changes in light
received by the
photo-detector
2
5
10
15
25
50
xxx
xxx
xxx
xxx
xxx
xxx
Printer
Waste fluid
3
Cleanliness Code Chart
Range
Code
300,000
200,000
150,000
25
160,000
24
100,000
80,000
23
50,000
40,000
30,000
20,000
15,000
40,000
22
29,000
21
10,000
10,000
20
5,000
5,000
4,000
3,000
2,000
19
2,500
18
1,500
1,300
1,000
17
320
500
400
300
200
160
150
16
15
14
100
80
13
50
40
30
20
40
12
20
15
11
10
10
10
5
4
3
2
1.5
5
9
2.5
8
1.3
1.0
7
.6
.5
.4
.3
.2
6
.3
5
Number of particles greater than size per milliliter
640
.05
.15
.1
4
.08
3
.04
2
.02
1
.01
2
1
5
15
10
20
Particle size in micrometers
20/14/12
Cleanliness Code
Example
4
Particle
size "X" in
micrometer
Number of
particles
greater than
"X" size in one
ml of test fluid
Range
code
2
5120
20
5
89
14
10
43
X
15
22
12
25
3
X
50
.4
X
25
30
35 40 45 50
Once the results are obtained, the
points are plotted on a Cleanliness
Chart. This chart has range codes (far
left edge) that give a number, 0 through
25, that corresponds to a specific number of particles. Taking the range code
for the number of 5µm and larger particles and the range code for the number
of 15µm and larger particles and combining them together with a slash (/)
gives us the ISO Cleanliness Code for
that fluid. For the particle count in the
example, the 89 particles of 5µm and
larger size are in the 14 range and the
22 particles of 15µm and larger is in the
12 range. This means the example fluid
is described as a ISO 14/12 cleanliness
fluid.
Unfortunately, the current ISO standard
does have a weakness in that it can
mask a significant build-up of very fine
silt sized particles by the non-reporting
of the counts smaller than 5µm. To
remedy this, Vickers has adopted, and
ISO is considering, expanding the code
to three ranges correlating to 2µm, 5µm
and 15µm. For the example presented,
the Cleanliness Code becomes 20/14/12.
Throughout this Vickers document we
will show cleanliness codes with 3
ranges, the last two being bold type to
signify that they are the current ISO
standard.
Sources of Contamination
There are four primary sources for solid
contamination to enter a hydraulic fluid.
They are: contaminated new oil, built-in
contamination, ingressed contamination
and internally-generated contamination.
Each of these sources needs to be
understood as each is a major consideration in filter placement.
Sources of Contamination
• Contaminated New Oil
• Built-in Contamination
• Ingressed Contamination
• Internally Generated
Contamination
Contaminated New Oil
Although hydraulic and lubrication fluids
are refined and blended under relatively
clean conditions, the fluid travels through
many hoses and pipes before it is stored
in drums or in a bulk tank at the user’s
facility. At this point, the fluid is no longer
clean as the fluid lines it has traveled
through have contributed metal and
rubber particles, and the drums have
added flakes of metal or scale. Storage
tanks are a real problem because water
condenses in them causing rust particles.
Contamination from the atmosphere
can also find its way into the tank unless
satisfactory air breathers are fitted.
Dirty New Oil
If the fluid is stored under reasonable
conditions, the principal contaminants
on delivery to the machine will be metal,
silica and fibers. With fluids from reputable
suppliers, sampling has shown typical
Cleanliness Levels of 17/16/14 or dirtier.
Using a portable transfer cart fitted with
a high efficiency filter, contamination
should be removed from new fluids
before the contamination enters and
damages the components in the system.
Contamination particles found in new fluid include rust, scale, fibers and sand
(photomicrograph at 100x).
5
Built-in Contamination
Sources of Ingressed
Contamination
• Reservoir Vent Ports
• Power Unit Access Plates
• Maintenance Events
• Cylinder Rod Seals
New machinery always contains a
certain amount of built-in contamination.
Care in system assembly and in new
component flushing reduces this but
never eliminates it. Typical built-in
contaminants are burrs, chips, flash,
dirt, dust, fiber, sand, moisture, pipe
sealant, weld splatter, paint and
flushing solution.
The amount of contamination removed
during the system flush depends not
only on the effectiveness of the filters
used, but also the temperature, viscosity,
velocity and “turbulence” of the flushing
fluid. Unless high velocities and
turbulence are attained, much of the
contamination will not be dislodged
until the system is in operation, with
catastrophic component failure a possible
result. Irrespective of the standard of
flushing executed by the machine builder,
an off-load period of “running-in” should
be regarded as essential for any new or
rebuilt hydraulic or lubrication system.
Ingressed Contamination
Contamination from the immediate
surroundings can be ingressed into the
fluid power or lubrication system. On
large installations, such as those within
steelworks or automotive plants, it is
relatively easy to know the environmental
conditions, though they vary considerably.
For example, a coke oven system
operates in conditions very different
from a similar system in a cold mill. For
mobile equipment, there is a very wide
variation in environmental conditions by
application, location and even by weather
conditions (i.e. high winds).
The key is to severely limit the access
environmental contamination has to
enter the hydraulic or lubrication system.
There are four major ways dirt can
enter a system: reservoir vent ports
6
(breathers), power unit or system
access plates, components left open
during maintenance and cylinder seals.
Sources of Ingressed Contamination
RESERVOIR VENT PORTS allow air
exchange into and out of the reservoir
to compensate for changes in fluid level
caused primarily by cycling cylinders
and thermal expansion and contraction
of the fluid. All vents that exchange air
need to be fitted with barrier-type air
breather filters. Other acceptable options
are to use bladders or flexible rubber
barriers to prevent the exchanged air
from coming in contact with the surface
of the system fluid or valving which
prevents air changes while allowing relief
protection against over-pressurizing
the reservoir.
POWER UNIT ACCESS PLATES —
In some plants it cannot be assumed
that access plates will always be
replaced, though this problem is not as
common as it once was. Good systemic
contamination control requires that
reservoirs are designed to remain
sealed during operation and any access
plates that need to be removed during
maintenance be easy to reinstall. The
most important factor in this aspect
of contamination control is the proper
education of all maintenance and
service personnel.
INGRESSION DURING MAINTENANCE —
Whenever a system is opened for
maintenance, there is an opportunity for
environmental contamination to enter
the system. All possible care should be
taken to ensure that open ports are kept
covered or plugged, and component
disassembly and rework is done in an
area that is protected from excessive
airborne dirt and contamination.
Generated Contamination
Lint free rags and oil absorbent materials
in “socks” (rather than loose glandular
form) should be used for component
wipedown and area clean up.
Generated Contamination
The most dangerous contamination to a
system is the contamination generated
by the system itself. These particles are
“work hardened” to a greater hardness
than the surface from which they came,
and are very aggressive in causing
further wear in the system. In a system
running on properly cleaned fluid very
few particles are generated, although all
components (especially pumps) create a
small amount of particles during routine
operation. In a system where these
particles are not quickly captured the
elevated contamination levels will cause
the number of additional generated
particles to increase at a highly accelerated rate! The best way to prevent
contamination generation within a system
is to start with a clean (fully flushed)
system and keep the system fluid clean.
CYLINDER SEAL INGRESSION — Rod
wiper seals rarely are designed to be
100% effective in removing the thin oil
film and the fine contamination from the
cylinder rod. Environmental dirt that
sticks to an extended rod is drawn back
into the cylinder and washed off into the
system fluid. Every effort should be
made during machine design to avoid
dirt or other contaminants from landing
directly on extended cylinder rods.
When this is unavoidable, the filters
should be positioned and sized to
capture this abundance of dirt.
Sources of Contamination
Generated
by cylinder
B
P
T
Adhesive Wear — Loss of oil film
allows metal to metal contact
between moving surfaces.
Fatigue Wear — Particles bridging
a clearance cause a surface
stress riser or microcrack
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.
Cavitation Wear — Restricted
inlet flow to pump causes fluid
voids that implode causing
shocks that break away critical
surface material.
Aeration Wear — Air bubbles in
the fluid implode breaking away
surface material.
Ingressed from cylinder rod
A
Abrasive Wear — Hard particles
bridging two moving surfaces,
scraping one or both.
Corrosive Wear — Water or
chemical contamination in the
fluid causes rust or a chemical
reaction that degrades a surface.
Generated by valve
Pressure
line filter
Transfer cart filter
Ingressed from
air breather
Return
line
filter
Generated
by pump
M
Built-in debris
Ingressed
through
reservoir
openings
M
Ingressed
from
new oil
Note: Suction strainers with bypass are shown as an option in many examples in this book.
See page 24 for a discussion on their application.
7
Damage Caused by Contamination
Contaminant particles come in all
shapes and sizes and are made up of a
wide variety of materials. The majority
are abrasive, so when they interact with
surfaces they plough and cut fragments
from critical surfaces in the components.
This abrasive wear and surface fatigue
accounts for almost 90% of degradation
failures.
Types of Failures
• Catastrophic Failure
• Intermittent Failure
• Degradation Failure
Types of Failures
Failures arising from contamination fall
into three categories:
1. CATASTROPHIC FAILURE occurs
when a large particle enters a pump or
valve. For instance, if a particle causes
a vane to jam in a rotor slot, the result
may well be complete seizure of the
pump or motor. In a spool type valve, a
large particle trapped at the wrong place
can stop a spool from closing completely.
Another example of catastrophic failure
occurs when the pilot orifice of a valve
is blocked by a large particle. Fine
particles can also cause catastrophic
failure; a valve, for example, can fail to
operate due to silting.
Interaction of Moving Parts
Motion
Particles of similar size to the clearance between
moving parts cause the most abrasive wear.
Larger particles cannot enter clearance, smaller
particles pass through without contact.
Clearance-size particles interact with both faces
simultaneously. Extra contamination is generated
by the disintegration of the moving surface. Larger
particles are “ground up” by the interaction in the
clearances.
8
2. INTERMITTENT FAILURE can be
caused by contamination on the seat of
a poppet valve which prevents it from
reseating properly. If the seat is too hard
to allow the particle to be embedded
into it, the particle may be washed away
when the valve is opened again. Later,
another particle may again prevent
complete reclosure and be washed
away. Thus, a very annoying type of
intermittent failure occurs.
3. DEGRADATION FAILURE can be
the result of abrasive wear, corrosion,
cavitation, aeration, erosion or surface
fatigue. Each one causes increased
internal leakage in the system components which reduces its efficiency or
accuracy, but these changes are initially
difficult to detect. The eventual result,
particularly with pumps, is likely to be
catastrophic failure. The particles most
likely to cause wear are clearance-size
particles which just bridge the critical
clearances between moving surfaces
in the component. Oil also suffers
degradation due to the presence of
excessive contamination.
Sizes of Critical Clearances
Manufacturing clearances within
hydraulic components can be divided
into two principal zones, i.e. up to
5 micrometers for high pressure
components and up to 20 micrometers
for lower pressure components. The
actual operating clearances for a
component are set by the type of
component and operating conditions it
sees. These clearances help to define
the cleanliness of the fluid required by
that component.
Mechanism of Fatigue
Stress risers
Crack forms
Force
Particle
1. First, stresses at component
surface develop and lead to elastic
deformation and plastic flow of material.
2. Then, small surface micro cracks
develop at or just beneath the solid
surface during component use.
Particles released
Cracks and faults coalesce
Repeated stress
3. The faults then join to form larger
voids undermining component surface.
4. Surface material then breaks away.
Pumps
Erosive Wear
Pressure port
Fluid flow
Metering edge
Metering edge
Spool
The metering edge of the spool and
valve land has been eroded away by the
particles in the high velocity fluid flowing
through the valve.
All hydraulic pumps have component
parts which move relative to one another,
separated by a small oil filled clearance.
Generally these components are loaded
toward each other by forces related to
area and system pressure.
Since the life of most pumps is
determined by a very small quantity
of material being removed from a few
surfaces, it follows that rapid degradation
and eventual seizure will occur if the fluid
within the clearance is heavily contaminated. The design of low pressure units
permits relatively large clearances and
typically only larger (10µm and larger)
contamination has a significant damaging
effect. Also at the lower pressure, there
is less force available to drive particles
into critical clearances. Increasing or
pulsating the pump pressure is of major
significance in determining the effect of
contamination on a pump.
9
Another factor affecting clearances
is the oil film thickness, which is also
related to fluid viscosity (film strength).
An optimum viscosity value is used
during design. The oil should provide
good film thickness to support loads
hydrodynamically, and also be thin
enough to allow adequate filling of the
pump without cavitation. It is generally
found in practice that critical clearances
are larger where higher viscosities are
used, and for this reason the maximum
viscosity which is compatible with the
inlet conditions should be chosen.
Similarly, good fluid temperature control
is beneficial in this respect.
Critical Clearances in a Vane Pump
Outlet
(high pressure)
Inlet
(low pressure)
Wear area:
tip of vane to ring
Wear area:
rotor to side plate
Wear area:
vane to vane slot
Inlet
(low pressure)
Outlet
(high pressure)
Critical Clearances in a Gear Pump
Wear area: tooth to case
Inlet
(low pressure)
Outlet
(high pressure)
Wear area: tooth to tooth
Clearance between teeth and
housing variable according to
position in rotation allowing
backflow of fluid with pressure.
Minimum clearance
10
Maximum clearance
The areas in pumps particularly subject
to critical clearance wear problems are:
Vane pump – Vane tip to cam ring,
rotor to side plate, vane to vane slot.
Gear pump – Tooth to housing, gear
to side plate, tooth to tooth.
Axial piston pump – Shoe to swash
plate, cylinder block to valve plate,
piston to cylinder block.
In many of these cases, the clearances
are effectively self-adjusting under
operating conditions, i.e. with increasing
pressure clearances becoming smaller.
Under adverse conditions, and particularly where there is shock loading, there
is an increased vulnerability to smaller
sized contamination particles. Even
where clearances are nominally fixed,
components under high loads may take
up eccentric positions which again make
them vulnerable to smaller particles.
From engineering data and field experience, Vickers has set recommended
contamination levels which, if achieved,
will result in an increased life for most
systems and components. These are
presented in the next section, which deals
with setting target cleanliness levels.
The useful life of a pump ends when it
no longer delivers the required output
at a given shaft speed. All too often,
degradation goes undetected until finally
catastrophic failure occurs, with vast
quantities of contamination being released
into the system. Following such a failure,
the life of the replacement pump will
be greatly reduced if the system is not
properly cleaned or protected.
To the end user, total cost is the most
important issue; the failure of a low-cost
pump may well result in expensive
downtime and maintenance. If, by the
inclusion of the proper contamination
control devices, such a failure can be
avoided, the initial investment in such
devices is fully recovered.
Motors
What has been written about pumps
applies generally to motors because of
their similar design. It must be remembered that a majority of the contaminant
passing through the pump will also
reach the motor where it will cause a
similar performance degradation. If, for
example, due to wear, the volumetric
efficiency of the pump falls to 85% of
its original value and the volumetric
efficiency of the motor falls to 90% of
original, then the overall volumetric
efficiency of the pump and motor will
drop to 0.85 x 0.9 = 76.5% of the
original value.
Hydrostatic Transmission
Hydrostatic transmissions most often
consist of a servo controlled pump and
a fixed volume motor. Wear to a critical
surface in any component will degrade
the overall performance of the transmission. Failure of a component can spread
debris throughout the system causing
extensive and expensive secondary
damage. High efficiency filtration is a
key factor in achieving long, reliable
service from a closed loop hydrostatic
transmission.
Directional Valves
In most directional valves, the radial
clearance specified between bore and
spool is between 4 to 13 micrometers.
As is well known, the production of
perfectly round and straight bores is
exceptionally difficult, so it is unlikely
that any spool will lie exactly central in
the clearance band. In a CETOP 3
valve, a spool is likely to have less than
2.5 micrometers clearance.
;;;;;
;;
;;;;
;;;;;
;;
;;;;
;;;;;
;;;;;;;
;;;;;
;;;;;
;;;;;
;;;;;
Critical Clearances in an Axial Piston Pump
Wear area:
piston to shoe
Wear area:
piston to cylinder block
Piston
Wear area:
shoe to
swashplate
Wear area:
cylinder block
to valve plate
Cylinder
Cylinder
block
Block
Swashplate
Valve plate
11
In an electrically operated valve, the
forces acting on the solenoid are: flow
forces, spring forces, friction forces and
inertia forces.
Flow, spring and inertia forces are
inherent factors, but friction forces are
to a great extent dependent on system
cleanliness. If the system is heavily
contaminated with particles similar in size
to the radial and diametrical clearances,
higher forces will be needed to move
the spool.
An even worse situation results from
silting, where contaminant is forced into
Valve Spool Critical Clearance
One large particle can bridge gap
Working pressure
Break in oil film due to
dirt concentration
;
;
;
Silt build-up
Valve Spool Clearances (with flows and forces)
To Actuator
*
From Pump
This situation occurs when valves
subjected to continuous pressure are
operated infrequently. Such valves
should preferably have local filtration
of a high efficiency in the pressure line,
but due account should be taken of
possible pressure surges generated
during component operation. The use of
filters as a special protection for single
units or groups of units can result in the
need for a large filter element of high
capacity, if the general cleanliness level
in the system is poor.
Some idea of the forces needed to break
this spool binding, compared with the
force available from the solenoid, can be
gained from the example of a CETOP 3
valve operating at 3000 psi (210 bar).
If a valve of this type remains in the
spring offset or energized position for a
lengthy period of time, silting takes place
between spool and bore and can cause
total immobility. The force needed to
overcome this state has been found
through experiments to be approximately
30 pounds, but both spring and solenoid
are designed to exert only 10 pounds.
The effect of the excessive silting can be
total system failure.
;
;
;
From Actuator
*
*
*
the clearances under pressure, eventually
leading to breakdown of the oil film and
spool binding.
*Silt collects in tight clearance leak paths causing increased resistance to shifting
12
To Tank
Solenoid Force
Pressure Controls
Flow Control Valve Throttle Sections
Abrasive particles in high velocity streams
of oil erode internal surfaces. This
situation is common to pressure controls,
particularly relief valves which are
subjected to maximum system pressure
drop. Pilot control stages generally see
low volumes at high velocities, and
heavy contamination affects both their
stability and repeatability.
Note: Throttle profile gives orifice segments of equal area
Flow Controls
The contamination tolerance of flow
control valves will depend very much on
the orifice configuration. Two different
orifices which are of entirely different
shape can have equal areas. The groove
type will tolerate a high contamination
level, except when used at low setting,
whereas a flat cut orifice is much more
prone to silting at all settings.
(a)
Bearing Wear
Typical clearance between
the rolling elements of a bearing
and the outer and inner race
can be less than 2µm.
Particles in the lubrication fluid
are rolled into this critical clearance
causing a surface micro crack,
initiating the spalling process.
With all types of pressure compensated
flow controls, the performance of the
pressure reducing element can be
considerably affected by contamination,
irrespective of valve setting. Damage to
the metering orifice can also occur,
which will become particularly apparent
at lower settings.
Generally speaking, all spool-type control
valves are affected by contamination in
the system, especially at high pressures.
The effects are likely to be magnified if
precise axial positioning of the spool is
necessary as, for example, in pressure
reducing valves where limited forces are
available to operate the spool. On the
other hand, poppet valves, though
affected by large particles of contamination, tend to be far more tolerant of silt
due to the self-cleaning action of the
seat. However, erosion of critical seat
surfaces must be avoided.
(b)
Inner race
(Shaft rotation)
Rolling elements
Outer race
(Stationary)
Bearings
In both rolling and siding contact
bearings, a thin oil film separates the
ball from the race or the journal surfaces
from the shaft. As long as there is no
direct contact between the moving parts,
the expected fatigue life of the bearing
approaches infinity. The most common
way for direct contact to happen is to
have a particle bridge the oil film and
contact a moving and stationary surface
at the same time. The resulting damage
is often a scratch or surface crack that
initiates the spalling process. In most
bearings, particles as small as 3µm can
have a negative impact on the life of the
bearing or system.
13
Piston/shoe Subassembly
FPO
Piston head contamination damage — Shoes can also become loose on the piston head as a
result of severe scoring and pitting from contamination.
Ruined Pistons
FPO
FPO
Telltale effects of contamination and seizing on the piston diameter can be seen in these
photos. Pistons in this condition cannot be reworked.
14
Examples of Wear on Actual Vickers
Components
Vickers guide to Pump Failure Analysis
contains many examples of failures
caused by contamination. Typical
contamination damage to a piston/shoe,
piston and cylinder block is shown here.
contaminants, wear will occur, thereby
generating further particles which may be
ground into many more smaller particles.
Fine particles, individually or in small
quantities, may not cause damage. But if
present in slightly higher concentrations,
they can lead to failure through silting.
Summary
As explained above, an individual large
particle arriving at the wrong place at
the wrong time can cause catastrophic
failure. A small quantity of silt-sized
particles can also cause problems by
eroding a surface or by building up in a
critical area.
Surfaces within components are
designed to be separated by an oil film,
the thickness of which may be continually
changing. When this gap is bridged by
Piston Pump Failures — Cylinder Block
FPO
The individual cylinder bores within a cylinder block are prone to excessive wear and tear.
This can be due to dry run, lack of lubricity in the fluid or contaminants. Cylinder blocks with
worn or scored bores should never be reused.
The top surface of a cylinder block that contacts the valve plate can also become scored or
pitted due to improper operating conditions such as aeration, cavitation, contamination and
high system temperature.
15
Setting a Target Cleanliness Level
Setting a Target Cleanliness Level
• Determine the cleanliness recommended for the most sensitive
component in system
• Adjust code for fluid type
• Adjust code for external factors
that increase the stress on the
system components
As stated previously, all hydraulic and
lubrication systems should have a target
cleanliness level for that specific system
clearly stated in their engineering documentation. This target should be set after
considering the components in the system (including the fluid), the typical operation and start-up temperatures, the duty
cycle, the systems’ required useful life
and safety issues. As the actual cleanliness level of the fluid varies by sampling
point within the system (i.e. reservoir,
pressure line, return line, etc.), the target
cleanliness level is assumed to be set for
the return line upstream of the return line
filter, unless stated otherwise.
Suggested Cleanliness Level for Good Component Life (circa 1976)
Note: This graph assumes viscosity to be within recommended range.
Pressure in PSI (bar)
4500
(306)
3000
(204)
Average hydraulic
components including
most pumps
Very sensitive
components
Very tolerant
components
1500
(102)
15/13/9
16/14/10
17/15/11
18/16/12
19/17/13
20/18/14
Contamination level
Note: Graph modified to show 3 code cleanliness levels
corresponding to the earlier ISO cleanliness codes.
16
21/19/15
22/20/16
23/21/17
In 1976, Vickers first issued a chart
giving suggested minimum cleanliness
levels for acceptable component life.
This graph has been the basis for much
that has been written and learned since
its publication.
The following chart and procedure
have been prepared to help design and
maintenance engineers set a target
cleanliness level. The cleanliness level
recommendations are based on engineering evaluations (including materials,
critical clearances and machining tolerances) and practical field experiences
with Vickers and other brands of
hydraulic or load bearing components.
Note: Vickers components are
designed and manufactured to high
standards that maximize their dirt
tolerance. Special materials, surface
preparations, and flow paths are
utilized to ensure reliable operation.
However, Vickers and all other brands
of components operate best on
properly cleaned fluids. Vickers has
prepared these recommendations
to help users of hydraulic and oil
lubricated machines maximize the
in-service life of their individual
components and the total system.
These recommendations are
more valuable than traditional
recommendations that focus on the
maximum allowable dirt rather than
the cleanliness needed for long,
trouble free operation.
Vickers Recommended Cleanliness Code Chart
How to Set a Target Cleanliness Level
PUMPS
STEP ONE
< 2000 PSI
Pressure
Fixed Gear
Fixed Vane
Fixed Piston
Variable Vane
Variable Piston
< 140 Bar
20/18/15
20/18/15
19/17/15
19/17/15
18/16/14
< 3000 PSI
210 Bar
19/17/15
19/17/14
18/16/14
18/16/14
17/15/13
< 3000 PSI
> 210 Bar
18/16/13
18/16/13
17/15/13
17/15/13
16/14/12
3000 PSI
210 Bar
20/18/15
19/17/14
19/17/14
20/18/15
20/18/15
18/16/13
20/18/15
18/16/14
18/16/13
18/16/13
18/16/13
18/16/13
18/16/13
16/14/11*
> 3000 PSI
> 210 Bar
19/17/14
19/17/14
19/17/14
20/18/15
19/17/14
17/15/12
19/17/14
17/15/13
17/15/12
17/15/12*
17/15/12*
17/15/12*
17/15/12
15/13/10*
3000 PSI
210 Bar
20/18/15
19/17/14
18/16/13
20/18/15
19/17/15
17/15/13
> 3000 PSI
> 210 Bar
20/18/15
18/16/13
17/15/12
19/17/14
18/16/13
16/14/12
3000 PSI
210 Bar
16/14/12*
> 3000 PSI
> 210 Bar
16/14/11*
VALVES
Pressure
Directional (solenoid)
Pressure (modulating)
Flow Controls (standard)
Check Valves
Cartridge Valves
Screw-in Valves
Prefill Valves
Load-sensing Directional Valves
Hydraulic Remote Controls
Proportional Directional (throttle) Valves
Proportional Pressure Controls
Proportional Cartridge Valves
Proportional Screw-in Valves
Servo Valves
ACTUATORS
< 2000 PSI
Pressure
Cylinders
Vane Motors
Axial Piston Motors
Gear Motors
Radial Piston Motors
Swashplate Design Motors
< 140 Bar
20/18/15
20/18/15
19/17/14
21/19/17
20/18/14
18/16/14
HYDROSTATIC TRANSMISSIONS
< 2000 PSI
Pressure
Hydrostatic Transmissions
(in-loop fluid)
< 140 Bar
17/15/13
BEARINGS
Ball Bearing Systems
Roller Bearing Systems
Journal Bearings (high speed)
Journal Bearings (low speed)
General Industrial Gearboxes
15/13/11*
16/14/12*
17/15/13 >400 RPM
18/16/14 <400 RPM
17/15/13
Using Vickers Recommended Cleanliness
Code Chart, determine the cleanest fluid
(lowest code) required by any component
in the system. All components that draw
fluid from a common reservoir should be
considered to be part of the same system
even if their operations are independent or
sequential (i.e. a central power unit running
several different machines). The pressure
rating for the system is the maximum
system pressure achieved by the machine
during a complete cycle of operation.
STEP TWO
For any system where the fluid is not 100%
petroleum oil, set the target one Range
Code cleaner for each particle size.
Example: If the cleanest code required
was 17/15/13 and water glycol is the
system fluid, the target becomes 16/14/12.
STEP THREE
If any two or more of the following
conditions are experienced by the machine
or system, set the target cleanliness one
level lower for each particle size.
• Frequent cold starts at less than
–18°C (0°F)
• Intermittent operation with fluid
temperatures over 70°C (160°F)
• High vibration or high shock operation
• Critical dependence on the system as
part of a process operation
Looking at the example above, if this
system was expected to cold start and a
failure could stop all production, the target
cleanliness would become 15/13/11.
Using this three-step procedure the
system target cleanliness code for the
system is now set.
*Requires precise sampling practices to verify cleanliness levels.
17
Achieving Target Cleanliness
Achieving System Cleanliness
• Select a filter with Bx = > 100
performance
• Select a filter with high strength
under system stress
• Locate the filters so that they see
sufficient system flow to capture
the contamination
• Select a filter which will provide
long in-service life
There are four major factors in positioning
contamination control devices in a
hydraulic or lubrication system to achieve
a target cleanliness level. They are:
• Initial filter element efficiency
• Filter element efficiency under
system stress
• Location and sizing of contamination
control devices in the system
• Filter element service life of the system
Nominal Filtration Rating
Absolute Filtration Rating
Filtration Ratio (Beta)
Nominal Rating — An arbitrary micrometer value indicated by the filter
manufacturer. Due to lack of reproductivity, this rating is deprecated.
Absolute Rating —The diameter of the largest hard spherical particle that will
pass through a filter under specified test conditions. It is an indication of the
largest opening in the filter element.
Filtration Ratio (ßn) — The ratio of the number of particles greater than a
given size upstream of the test filter divided by the number of particles of the
same size downstream of the test filter.
The Multipass Filter Performance Test
Recirculating test stand fluid
slurry
Downstream
particle counter
Test Filter
Upstream
particle counter
18
The international standard for rating the
efficiency of a hydraulic or lubrication
filter is the Multipass Filter Performance
Beta Test (ISO 4572). The results of this
test are reported as a ratio of number
of particles greater than a designated
size upstream of the test filter compared
with the number of same size particles
downstream of the test filter. These results
are then expressed as a Beta ratio.
Multipass testing has greatly aided
engineers in the development of better
and more efficient filter elements, and
it has helped the design engineer who
needed to specify a filter element’s
performance. But, there’s little correlation between multipass efficiencies
and system cleanliness needs. In the
final performance analysis, the goal is
properly cleaned fluid and not just very
high Beta ratios and dirt capacity. The
most important information needed by a
designer or user of a hydraulic system is
Filter Ratings
Fresh contaminant
Filter Element Initial Efficiency
Beta Ratios and
Corresponding Efficiencies
Beta
Ratios
1
2
5
10
20
75
100
200
1000
5000
Efficiency
0%
50.00%
80.00%
90.00%
95.00%
98.70%
99.00%
99.50%
99.90%
99.98%
Beta ratios and dirt capacity are only a
guide to system cleanliness needs.
the system cleanliness they can expect
when that filter and media are properly
installed in the system.
Each grade of Vickers high efficiency
filter media construction is thoroughly
multipass tested and then rated with the
system cleanliness level expected to be
achieved with the use of that product.
The assumptions behind these cleanliness ratings are: 1) the filter sees full
system flow, 2) the filter is the primary
filter in the system, and 3) air breathers
along with recognized maintenance
practices will limit dirt ingression from
the atmosphere.
Vickers Media Construction
Coated Steel Mesh
Non woven synthetic
diffuser layer
Proprietary Vickers glass
micro fiber media with
special resin binder
Non woven synthetic
diffuser (drainage) layer
Coated Steel Mesh
Limits on Correlation Between “Beta” and System Cleanliness and
“Dirt Capacity” and Service Life
Laboratory Procedure
Real World
Pressure Rise
One gradual rise
Thousands of changes
Fatigue Cycles
One
Millions
Element Aging
Minutes
Months
Element Life
One hour
800+ hours
Contaminant
AC fine test dust
Debris, water, gas
Challenge Rate
Constant
Always changing
Fluid Used
MIL 5606
Wide variety
Temperature
100°F (38°C)
-20°F to 200°F (-7° to 93°C)
Flow
Steady
Thousands of changes
19
Filter Efficiency Under Stress
System Cleanliness Ratings
Code
Number of times flow from pump passes
through the system filters (See Note 1)
Typical ISO 4406 cleanliness
level achieved (See Note 2)
03
2.0
1.5
1.0
.5
14/12/10
15/13/11
16/14/12
17/15/13
05
2.0
1.5
1.0
.5
16/14/12
17/15/13
18/16/14
19/17/15
10
2.0
1.5
1.0
.5
18/16/14
19/17/14
20/18/15
21/19/16
Note 1
Note 2
Systems Flow
Passes thru Filters Typical Filter Placements
2.0
Full flow pressure and return
1.5
Full flow pressure or return
and recirculation loop
1.0
Full flow pressure or return line
0.5
Recirculation loop sized to 15%
of system volume per minute
Cleanliness level achieved is affected by
percentage of system flow that passed thru
the filters, filter housing integrity, element
performance and contamination ingression
and generation rates. For more detailed
assistance, please contact your local
Vickers Distributor.
For target cleanliness level selection assistance and proper filter placement guidelines,
consult your local Vickers Distributor.
Changes in Flow
In poorly supported elements, changes in flow and pressure drop cause the
sides of element corrugations to flex and the root to stretch, giving rise to fatigue
stresses. Dirt capacity is also lost as areas of the medium have no flow.
No flow
Deflection under
high flow
Flow directions
Filter medium
High stress under
high flow conditions
causes pleat to deform.
20
Flow fatigue failure is
commonly at root of pleat.
A major problem in correlating multipass
test claims to real world fluid cleanliness
levels is that real systems operation
greatly stresses the element. In active
systems, flow rate changes (often several
a minute), pressure pulses (hundreds a
minute), decompression shock waves,
cold starts, and other variables all work
to degrade a filter’s performance. In
multipass testing the element is subject
to one gradual rise in differential pressure
as the element loads!
Flow fatigue test protocol (ISO 3724)
leaves many important questions unanswered. Again the element is tested
in laboratory conditions that cannot
duplicate the interaction of the many
forces working to stress and degrade
the element. This laboratory test may
fail to answer the question of how an
aged element will perform during the
latter part of its service life.
The best way to deal with this issue is
to look at the construction and feel the
element pleats. Are the pleats well
supported? Do they flex under hand
pressure? Any element that fails these
simple tests will fail to maintain efficiency
and integrity, and will not maintain the
targeted cleanliness level.
Additionally, look at the pack construction. Steel wire mesh is very important
in element construction. Wire keeps the
pleats from flexing, and gives the filter
medium the support it needs to keep from
failing due to fatigue. The downstream
wire mesh also serves as a last chance
protection in case of unexpectedly severe
stress that causes element media rupture.
Elements without downstream wire
mesh are not recommended for use in
hydraulic or lubrication systems with
even mild stress. This rule is important
as the relatively higher cost of wire
mesh has lured some filter manufacturers to take the wire mesh out and use
cheaper substitutes without dealing with
the real world issues of stress and last
chance protection.
Filter Matrix Breaking
Without proper support, the fibers forming the bonded media layer
can deform, allowing contamination to pass through the filter.
Supported fiber matrix after repeated stress
Inadequately supported matrix after
repeated stress
Filter Placements
This chart helps the engineers select the grade of media and the filter placement(s) that will achieve the required target
cleanliness. It assumes the system will experience “average” ingression and that maintenance of the system will be consistent
with current technology. If in operation the system is running dirtier than expected, corrective actions should be initiated. Suggested
corrective actions are:
Target Cleanliness
1. Consider using a finer grade of media.
2. Add a filter to the system.
14/12/10
03
03
03
15/13/11
03
03
05
16/14/12
03
05
05
05
03
17/15/13
03
05
05
05 or 10
03
03
18/16/14
05
10
05 or 10
10
05
03
19/17/15
05 or 10
10
10
10
05 or 10
05
Full flow pressure line
and return line
Pressure or return
and recirculating loop at
20% of system volume
per minute
Pressure line plus
return line plus
recirculating loop
Recirculating loop
at 20% of system
volume per minute
Recirculating loop
at 10% of system
volume per minute
Recommended filter
placements for high
ingression systems
with fixed volume
pumps
Recommended filter
placements for
systems with variable
volume pumps
Recommended filter
placements for high
ingression systems
with variable
volume pumps
Full flow pressure line
or return line
Note: All systems need a sealed reservoir with 3 micron air filtration.
21
Locating Contamination Control Devices
Hydraulic Systems — Open Loop
Locating Contamination Control
Devices in Open Loop Applications
Main System Contamination Control
• Pressure Line
• Return Line
• Recirculating Loop
Component Isolation
• Sensitive Components
• Safety Issues
Filter placements in hydraulic systems
can be categorized by the three major
functions they can perform. These
are: ingression prevention, system
cleanliness maintenance, and component isolation.
Ingression prevention
All air entering the reservoir needs to
be filtered. Removing dirt from air is
many times easier than removing it from
oil. The first step is to make sure the
reservoir is sealed and to ensure that
the exchange air enters the reservoir
only across sufficiently-sized air filters
Pressure Line Filter
(to system)
Check valve
Relief
valve
Pressure
line filter
Pump
Tank
Pressure and Return Line Filtration
A
B
A
B
A
B
A
B
P
T
P
T
P
T
P
T
M
22
Duty cycle.
System continuously
on-load with frequent
actuator operation.
Filter bypass setting:
p = (50 psi) 3,5 bar
Pump
outlet:
30 L/min
All fluids entering the system should
pass through a high efficiency filter
(grade “03”) before they are added to a
system. This is often accomplished by
fitting a Transfer Cart with a filter directly
downstream of the pump and then using
a quick connect coupling (half mounted
to the reservoir, half on the discharge
hose) requiring the fluid to be pressure
pumped into the reservoir. An alternate
plan is to have a procedure that requires
the fill fluid to pass through the return
line filter to enter the system. A third
alternative is to use the recirculating
pump as a fill pump with the filter in the
kidney loop to clean the new oil.
Maintaining System Cleanliness
Pressure Line Filters
• Fixed Volume over 2250 psi
(155 bar)
• Variable Volumes over 1500 psi
(103 bar)
• System with Servo or Proportional
valves
Filter bypass setting:
p = (50 psi) 3,5 bar
that are able to extract particles of a size
of 3 µm or more from the air. The port(s)
needs to be fitted with a Vent Filter
designed to remove particles 3 µm and
larger from the air (grade “10”).
There are three main places in a circuit
where contamination control filters
should be located: Pressure line(s),
Return line(s), or Recirculating loop.
A pressure line filter should be fitted
directly downstream of any fixed volume
pump operating over 2250 psi
(155 bar) and any variable volume pump
operating over 1500 psi (103 bar). The
rotating group of a pump has a mixture
of sliding and rolling contact surfaces
which are stressed by high pressure or
changing pressure operation. As such,
an operating pump is always producing
some wear debris. For systems with
servo or proportional valves, a high
pressure filter should always be used
regardless of pump type or pressure.
The pressure line filter should be considered the total system contamination
control device only if it sees maximum
pump flow during more than 60% of the
machine duty cycle. If no additional
return filter is used, this layout allows
the dirt returned from the system to
pass the pump, therefore causing
increased wear in the pump before it is
filtered out.
The return line is an excellent location
for the main system contamination control filter, as long as it sees at least 20%
of system volume each minute. In cases
where return line flow is less than the
20% minimum (periods of operation with
the pump in compensation), a supple-
mentary recirculating pump and filter
should be designed into the system.
Often systems that need recirculating
filters also need off-line cooling loops;
both these needs can be met by a single pump/motor with the filter upstream
of the cooler.
the piston area and rod side piston area
mean that during part of the machine
duty cycle flow rates can be 2 times
pump flow or more. In systems with
very high or severely pulsating flows,
recirculating loop filters are often the
best choice.
Flow amplification can cause problems
for return line filters. Cylinders with a
2:1 or greater differential area between
Return Line Filtration
Off Line Filtration System
Linear actuator
A
B
A
B
A
B
A
B
P
T
P
T
P
T
P
T
Filter setting:
p = 2,5 bar
(35 psi);
Bypass:
p = 3,5 bar
(50 psi);
M
Basic arrangement of
return line filtration.
A
B
P
T
Directional valve
Relief valve
Off-line pump:
56 L/min
(15 gpm)
Return line
filter
M
Reservoir capacity: 220L (60 gal.)
Duty cycle. Pump on load continously meeting the flow demands with pressure
compensated control.
M
Tank
23
Component Isolation
Component Isolation
Protects:
• High Cost Components
• Safety Functions
• Against High Cost Downtime
Protects Sensitive Components:
• Servo Valves (all brands)
• Proportional Valves (all brands)
Filters to isolate components should be
considered for systems or machines to
protect downstream components in the
event of a pump or other major component failure. Additionally, certain classes
of components need dedicated protection based on their design clearance or
fine metering edges.
Whenever a primary failure can cause
a secondary failure with unacceptable
consequences, an isolation filter or
strainer should be placed upstream of
that component. Since pumps have
finite life and as they fail the debris
travels downstream to the valves, care
should be taken to place a strainer in-line
ahead of any valve that has a safety
consideration or critical function to
the system.
Servo and proportional valves have fine
tolerance spools that modulate in reaction to small changes in pilot flow or
proportional solenoid forces. Even
small quantities of fine silt can cause
degraded operation. Individual valves or
banks of valves should be isolated with
a non-bypass filter that protects these
components from silt and chips that
could enter a system during maintenance
of other components. For large servo or
proportional valves with external pilot
flow, a smaller, less expensive non-bypass
filter 1 can be placed in the pilot line
while the main valve is protected by the
system filter 2 . Filter 3 is an optional
location. A common mistake that should
be avoided is selecting a component
24
isolation filter that is finer than the
system filter. This forces the isolation
filter to perform the general system
clean-up function, and results in very
short element life.
A location not recommended for filter
placement is in the case drain flow
from open or closed loop pumps. The
shaft seal on all pumps must maintain
a zero leak seal under very low differential pressure conditions. These seals
experience accelerated wear whenever
additional back pressure is added to the
pump case. If a filter is being considered
in a case drain application it should be
reviewed with consideration of the
effect it will have to the shaft seal life.
Pressure Line Filtration
(to system)
Relief valve
Pump
Tank
Pressure line filtration
with a fixed pump and
a non-bypass filter.
Tank
Hydraulic Systems–Closed Loop
Closed Loop Hydrostatic Transmission
The fluid cleanliness level that is significant to a closed loop hydraulic system’s
long-term dependability is the “in-loop”
fluid cleanliness. Normally a high efficiency filter in the charge pump line will
maintain the required cleanliness. But,
for hydrostatic transmissions running at
or near their maximum pressure, in-loop
filters with reverse flow valving are recommended. These filters will also protect
the motor in case of a pump failure.
Remember to consider the percentage
of time the transmission runs in each
direction when locating the filter. For bidirectional operation with approximately
50% of the duty cycle in each direction,
two filter housings should be used.
Motor
valve
package
2
M
1
M
1. Off line filtration as main
operating filtration
2. High efficiency filter on charge
flow (preferred location)
Non Bypass Filter Ahead of a Servo Valve
X
A
B
P
T
Y
X
A
B
P
T
Y
T
1
From other
functions
3
Non-bypass
filter in the
pillot line of
a servo valve
Non-bypass filter
in the pressure line
of a servo valve
P
Relief
valve
To other
functions
Pump
M
2
Return line filter for
system containment control
Note: Return line filter grade
should be as fine or finer than
the non-bypass filters
25
Lubrication Systems
Central Lubrication System
There are two locations for filters in a
lubrication system: pressure line and
recirculating loop. For pressure line
operation, the filter should be “duplexed”
allowing for on line element change while
the system is in operation. Recirculating
loop filters are excellent (application
location) as long as the loop flow is at
least 50% of the main pump flow.
to bearings
Filter Condition Indicators
Relief valve
Filter
Pump
M
M
Cooler
Central lubrication system with Duplex filters
and a recirculation cooling and filtration loop.
Filter Condition Indicator
• All filters should be fitted with a
condition indicator
After the filters are placed within the
system, the next consideration is how the
user is going to know when to change
the element. The answer recommended
in DIN 24550 standard is to have all
filters fitted with a differential pressure
indicator that gives an easy-to-read
indication that the element needs to be
changed. Vickers indicators are designed
to indicate at a pressure drop 20%
below the bypass setting which equates
to 95% of the element’s service life. This
indication before bypass feature was
incorporated to allow safe operation of
the machine until the next shift change or
convenient maintenance opportunity.
Element Differential Pressure Build-up with Dirt Loading
Bypass valve cracking pressure
Setting
Initial element
Pressure drop
{
Differential pressure across element
Indicator
Time in service (increasing dirt loading)
26
5% of element service life
Flushing New or Rebuilt Systems
The most critical time in the life of a
hydraulic or lubrication system is the
initial run-in period. During this time
much of the manufacturing debris in
the components and any debris added
during the assembly process are washed
through the system. It is critical that this
contamination be captured quickly and
removed from the system while it is in
off-load operation.
New System Flushing
There are three steps to a flushing
process. First, the machine must feed
system fluid through all lines and components. Second, this process must
dislodge the dirt from all components
and lines, and third, the contaminations
must be captured with a high-efficiency
filter. Dislodging and transporting dirt
is best accomplished by using a low viscosity fluid traveling at high line velocity.
Special flushing fluid can be used or
the actual system hydraulic fluid can be
used at an elevated temperature. To
get flow through all the lines, all the
valves should be operated several
times. In some cases, lines need to be
connected around a component to allow
high flow fluid to travel through the line.
Capture of the debris to flush to a cleanliness level of 16/14/11 reasonably
quickly is best accomplished with a
Vickers filter using “05” media. This
product has the combination of high
efficiency and high capacity needed to
achieve a successful flush.
Element Service Life
As in any aspect of machine design or
maintenance, cost of installation and
operation is a very important concern.
For filters, the length of time an element
lasts in service, and the initial cost of
that element, combine to determine the
economics of using that product.
The most important aspect of gaining
long element service life is to minimize
the ingression! Reservoirs need to be
< 3µm) that remove
fitted with vent filters (=
the dirt before it enters the system.
Access port and doors need to be kept
sealed so that dirt cannot be drawn into
the system. Cylinder rods that extend
into contamination laden environments
should be shielded to minimize the dirt
being drawn into the system.
The second important aspect to long
element service life is to keep the cleanliness level of the fluid at or below target.
Periods of machine operation with dirty
fluid cause accelerated internal wear that
loads a filter element. (It’s important the
debris is caught as it saves the system,
but it does cost the element part of its
service life.) Always change an element
on indication and always use genuine
Vickers elements because of their
consistent performance and superior
strength under stress.
New System Flushing
• Dislodge the dirt and transport
it to the filter
• Flow fluid through all lines and
components
• Capture the dirt with a high
efficiency filter
Element Service Life
• Minimize ingression
• Maintain a constant cleanliness
• Use an element with high dirt
capacity
• Use elements with greater
media area
Flushing target cleanliness levels should
be two ISO codes below the target
cleanliness level for system operation.
When the new oil is introduced into the
properly flushed system, less time and
filter element life will be consumed
reaching system equilibrium.
27
Vickers elements are designed to give
long life and reliable service in hydraulic
or lubrication applications. This is
achieved with our multi-layer construction. Each layer provides additional
strength or capacity leading to overall
superior performance. Some elements
focus heavily on media structure only,
which can give increased “dirt capacity”
under laboratory conditions, but no
increase in service life is experienced
in real systems.
An often overlooked aspect of dirt
capacity and service life is the effect
of element area. When comparing an
element of “x” area with an element of
“2x” area, one would expect twice the
life for the larger element. But, in real
systems, the life extension is most often
between 2.5 and 3.5 times as long. This
is because the reduced flow density
through a unit area of media allows for
more effective contaminant capture.
Larger elements are the most cost effective approach to contamination control
from the perspective of operating costs.
Element Service Life versus
Element Area
11
10
9
Ratio of service life increase
The third issue in long element service
life is the “dirt capacity” of the element.
This value is calculated as part of the
multipass efficiency test. Because of the
many differences between the test conditions (Fine Test Dust [ACFTD] contamination, single pressure rise, etc.) and
real system operation, different dirt
capacity values do not correlate well to
changes in element service life. Dirt
capacity can only be used to compare
elements under very specific laboratory
situations, and as a result published dirt
capacity values should be used as general information rather than specific
comparable data.
8
7
6
5
4
3
2
1
1
2
3
4
5
6
Ratio of filter area increase
28
7
8
Confirming and Monitoring Achievement of Target Cleanliness
Once the target cleanliness level has
been set, and the filters have been
selected and located in the system, the
last and ongoing step is to confirm and
monitor that the target cleanliness is
being achieved. The best way to confirm
the target is being reached is to take a
representative sample from the return
line, ahead of the filter and send it to a
qualified laboratory that reports particle
counting per ISO 4406 (modified to
include 2µm counts).
Quality laboratories, like the Vickers
Fluid Analysis Service, report the cleanliness level with three ranges codes
corresponding to 2µm, 5µm, 15µm.
From this information, it is possible to
determine that the hydraulic or lubrication system has the clean fluid it needs
for long dependable operation.
New developments in the environmental
sciences have resulted in passage of
laws concerning the disposal of used
hydraulic or lubrication fluids. Cost
conscious users of petroleum products
have discovered that it is far more cost
effective to extend useful oil life by as
much as 4-6 times through better
contamination control and Systemic
Contamination Control practices, thereby
avoiding the high costs of frequent
replacement and disposal of aged fluids.
For more detailed information on how
you can realize these savings contact a
Vickers distributor trained in systemic
contamination control.
Taking A Representative Sample
Taking a representative sample is a very
exact science. Generally, the right place
to sample a system is in the return line
directly ahead of the return line filter.
It is good system design to install a permanent sampling valve in that location.
Alternate locations for sampling are to
take a reservoir sample using a vacuum
pump and clean tubing, or sampling from
the pressure line directly downstream of
the pump. An important factor with reservoir sampling is to be sure the end of the
sampling tube is about half way down
into the fluid, otherwise “stratification”
within the reservoir can cause the sample
to be non-representative. Reservoir
sampling is the least recommended
alternative because of the potentially
inconsistent sampling and the need to
open the system, inviting contamination,
to obtain the sample.
Fluid Sampling Kit
Monitoring System Cleanliness
• Sample from the return line ahead
of the return line filter
• Sample from an active system
• Obtain particle counts for 2 m,
5 m and 15 m
New Oil versus Filters
• The high financial and environmental cost of oil disposal makes
filtering the better option
FPO
Vickers Fluid Analysis service provides: Ultra clean sample bottle • Sampling instructions
• Submittal form • Protective bag • Mailing box
29
In all sampling situations it is critical
that the system be in operation or just
shut down when the sample is taken.
This assures that the fluid is turbulent
and that the contamination in the
system is circulating and available to
be captured in the sample bottle.
Recommended System Sampling Frequency Chart
Systems with target cleanliness 17/15/12 or lower
System Pressure
< 2000 psi
2000 - 3000 psi
> 3000 psi
(140 bar)
(140 - 210 bar)
(210 bar)
8 hours of operation
per day
4 months
3 months
3 months
Over 8 hours of operation
per day
3 months
2 months
2 months
< 2000 psi
(140 bar)
2000 - 3000 psi
(140 - 210 bar)
> 3000 psi
(210 bar)
8 hours of operation
per day
6 months
4 months
4 months
Over 8 hours of operation
per day
4 months
3 months
2 months
Systems with target cleanliness 18/16/13 or higher
System Pressure
Note: Initial commissioning or major rebuild
Large system (2000 liters (530 USgal) or more) and systems with servo valves
• Sample fluid before start-up
• Sample fluid during first day running
• Sample fluid after one week
• Sample after one month operation
Other systems
• Sample during first day running
• Sample after one month operation
Systems in distress or immediately after a maintenance event
(i.e. increased heat, erratic operation, unusual sound, etc.)
• Immediate
30
Once the cleanliness level has been
achieved and confirmed, normal maintenance practices dictate that a system
be resampled at regular intervals to
reconfirm that the proper cleanliness
level is being maintained.
If the cleanliness level code value rises,
meaning the system is running dirtier
than it should, the first thing to check is
if new ingression is entering the system.
Check to be sure that all access doors
are closed and that the vent filters are
fitted and operational. Next, check to see
if the filters are on bypass; if so, replace
them with the appropriate genuine
Vickers filter elements. Lastly, it may be
necessary to add a filter to the system.
The most common solution is to add
a recirculating loop, (pump, motor and
filter) to the reservoir.
After any maintenance activities which
may introduce contamination, such as
hose replacement or pump repair, a
new sample should be taken to confirm
that the target cleanliness level is still
being maintained.
ProActive Maintenance
An important new technology currently
being developed for hydraulics and
lubrication systems is ProActive
Maintenance. The concept, a significant
part of systemic contamination control,
is to place sensors in the fluid flow and
allow their outputs to be combined and
computer analyzed to make diagnostic
statements about the operational health of
the machine. This emerging technology
holds great promise for increasing the
reliability of fluid power and oil lubricated
machines. Vickers is the leader in the
development of both Systemic
Contamination Control and ProActive
Maintenance technology.
EATON WARRANTY EXTENSION
Eaton is committed to the practice of
systemic contamination control
and superior performance of our filter products.
Eaton will extend by three years, the standard
warranty on all Eaton products used in a system
that is protected by Eaton filters (and elements)
applied consistently with the principles
presented in this document.
Eaton Support
Eaton is committed to assisting users
of hydraulic and lubrication systems to
achieve the long reliable service life
designed into these systems. Our factory
and distributor personnel are well trained
in systemic contamination control and
can help both design and maintenance
engineers. If you have any questions, or
need additional assistance, please feel
free to call Eaton or our local distributor.
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© 2002 Eaton Corporation
All rights reserved
Printed in USA
Document No. 561
October 2002