Handbook Of Filtration

The Handbook of
Hydraulic Filtration

The Handbook of Hydraulic
Filtration is intended to
familiarize the user with all
aspects of hydraulic and
lubrication filtration from
the basics to advanced
technology.

It is dedicated as a reference
source with the intent of
clearly and completely
presenting the subject matter
to the user, regardless of the
individual level of expertise.The selection and proper use
of filtration devices is an
important tool in the battle to
increase production while
reducing manufacturing costs.
This Handbook will help the
user make informed decisions
about hydraulic filtration.

Table of Contents
SECTION

PAGE

Contamination Basics

2

Contamination Types and Sources

4

Fluid Cleanliness Standards

12

Filter MediaTypes and Ratings

16

Filter Media Selection

20

Filter Element Life

22

Filter Housing Selection

24

Types and Locations of Filters

28

Fluid Analysis

32

Appendix

34

1

Contamination Basics

Filtration Fact

Contamination Causes
Most Hydraulic Failures

Properly sized, installed, and

The experience of designers and users
of hydraulic and lube oilsystems has
verified the following fact: over 75% of
all system failures are a direct result
of contamination!

maintained hydraulic
filtration plays a key role
in machine preventative
maintenance planning.

Filtration Fact

The cost due to contamination is
staggering, resulting from:
▼ Loss of production (downtime)
▼ Component

replacement costs

If any one of these functionsis
impaired, the hydraulic system will not
perform as designed. The resulting
downtime can easily cost a large manufacturing plant thousands of dollars
per hour. Hydraulic fluid maintenance
helps prevent or reduce unplanned
downtime. This is accomplished
through a continuous improvement
program that minimizes and removes
contaminants.

Contaminant Damage

The function of a hydraulic▼ Frequent

filter is to clean oil, but the

▼ Costly

ultimate purpose is to

▼ Increased

overall maintenance costs

▼ Formation

reduce operating costs.

▼ Increased

scrap rate

▼ Chemical

compound formation

▼ Depletion

of additives

▼ Biological

growth

Filtration Fact
The disposal cost of a
drum of waste oil can be
4X - 5X the cost of a
drum of newoil.

fluid replacement

disposal

Functions of Hydraulic
Fluid
Contamination interferes with the four
functions of hydraulic fluids:
1. To act as an energy transmission
medium.
2. To lubricate internal moving parts of
components.
3. To act as a heat transfer medium.
4. To seal clearances between moving
parts.

2

Actual photomicrograph of particulate contamination
(Magnified100x Scale: 1 division = 20 microns)

▼ Orifice

blockage

▼ Component

wear

of rust or other oxidation

Hydraulic fluid is expected to create a
lubricating film to keep precision parts
separated. Ideally, the film is thick
enough to completely fill the clearance
between moving parts. This condition
results in low wear rates. When the
wear rate is kept low enough, a component islikely to reach its intended life
expectancy, which may be millions of
pressurization cycles.

Contamination Basics
The actual thickness of a lubricating
film depends on fluid viscosity, applied
load, and the relative speed of the two
surfaces. In many components, mechanical loads are to such an extreme
that they squeeze the lubricant into a
very thin film, less than 1 micrometerthick. If loads become high enough, the
film will be punctured by the surface
roughness of the two moving parts.
The result contributes to harmful
friction.

Typical Hydraulic
Component Clearances
Component
Microns
Anti-friction bearings
0.5
Vane pump (vane tip to outer ring)
0.5-1
Gear pump (gear to side plate)
0.5-5
Servo valves (spool to sleeve)
1-4
Hydrostatic bearings
1-25...