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Hydraulic Filtration and Contamination

All hydraulic systems have a common need for protection from harmful contaminants. Good contamination control means cost effective filtration. Filtering out the particles large enough to be harmful to your system prevents damage and allows the longest possible equipment life. Minimizing maintenance costs through good contamination control practices requires proper filter application based on the specific contamination problems.
Contaminants, the natural enemy of hydraulic systems, cause more than 70% of all failures. If not controlled, particles too small to be seen can reduce hydraulic system efficiency. System efficiencies may be reduced as much as 20% before it is recognized that something is wrong.

Contamination affects hydraulic systems in many ways.

  • Corrosion of hydraulic systems from acids that form due to fluid breakdown and mixing of incompatible fluids in the system.
  • Increased internal leakage lowers the efficiency of pumps, motors, and cylinders, decreases the ability of valves to control flow and pressure accurately. Internal leakage also wastes horsepower and generates excess heat.
  • Sticking of parts due to sludge or silting. Silting is a collection of fine particles in critical areas, which will impair proper system operation.
  • Seizure of parts or components caused by large amounts of contaminants becoming lodged in the clearances.

Several possible sources of system contamination.
1. contamination built-in at the point of manufacture
2. hydraulic fluid contamination (filling)
3. system wear contamination
4. contamination introduced through servicing

Built-in contamination, or primary contamination, is caused during the manufacture, assembly and testing of the hydraulic components.Metal fittings, small burrs, pieces of Teflon tape (other sealing compounds), sand and other contaminants are routinely found in newly manufactured systems. These contaminants can be the most damaging particles to your system. Filtering them out immediately with a fine filter will prevent early catastrophic system failure, or system leakage problems.
Ingressed or external contamination comes from the environment. Dirt can enter the hydraulic system through worn rod seals, breather caps and worn cylinder rods.

The internal operation of the system generates contaminates that need to be removed. Internal rod ends, valve spools, pump vanes, gear wipe and hoses all generate minute particles that will contaminate a hydraulic system.

As systems are checked and disassembled for inspection or repair, the system is vulnerable to dust and air borne contaminates. Dust and air borne contaminates will adhere to filler caps, breathers, funnels, transfer pumps, and replacement parts. Care must be taken during all repairs to keep the system free of contaminates.
In order to work on hydraulic systems properly and safely, you should:

  • clean exterior surfaces of dust, dirt, oil, etc. before removing covers
  • make sure new parts are clean
  • keep parts protected prior to assembly
    protect system openings – use covers, tape, plastic wrap, etc.
  • clean transfer containers, funnels, nozzles, etc.
  • don’t remove filler screens
  • use clean-out filters to clean system after assembly.

This article is an excerpt from a technical service bulletin from the Filter Manufacturers Council.

A Simplified Study in Filtration

Filtration has come a long way since the beginning of time. It goes all the way back to ancient times. The Egyptians used to strain their grape juice through fabric. Even the use of filters to purify water and make it fit for consumption is not new.

Historical records dating back before the birth of Christ have many references to making water drinkable. The Bible has many references to water treatment and supply. Egyptians heated, then filtered their water through sand. Ancient Indo-European records refer to placing water in copper kettles, heating it, exposing it to sunlight, and running the water through charcoal. In ancient Rome around 300 B.C., water provided by the aqueducts was used not only for drinking but for bathing. Primitive filtration systems were used in the form of settling tanks to remove large debris from the water to help purify it.

Just so you have a basic understanding of the relative size of particles, the human eye can see no smaller than 40 micron ( .0015 of an inch), human hair averages 50-70 micron (.002 of an inch) in diameter, a grain of table salt is about 100 micron, white blood cells are 25 micron, red blood cells are 8 micron, and most bacteria (cocci) is about 2 micron. Now that’s small!

How does all this information relate to the filtration of fluids in our hydraulic systems? Generally speaking, people do not place much emphasis on filtration. However, it is one of the most important aspects of a system. Pump efficiency is destroyed or at the least is degraded because the simple, inexpensive, filter system was not maintained or maybe never existed in the first place.

– this condensed article was taken from Flow Ezy Filters Product and Service Newsletter Fall 2001