TECHNICAL
NOTES ON CONTAMINATION CONTROL:
HYDRAULIC SYSTEM PROBLEM PREVENTION
Fekadu Mengistu
Workshop Manger, Ries Engineering
Published in the Journal of the ESME, Vol. III, No. 1, September
2000
Reprinted with ESME
permission by the African
Technology Forum
ABSTRACT
A hydraulic system of an equipment or machinery is a carefully balanced interdependent network. Hydraulic components are designed to work together to deliver required performance. Every day, however, many factors work to erode their efficiency and performance. Today’s industry trend in design and manufacturing is more and more towards sophisticated systems, tighter clearances and higher pressures. These new systems are, therefore, easily susceptible to contamination. This article discusses and describes the main factor which robs hydraulic systems performance - contamination.
What are
Contaminants?
Particulate Contaminants
Chemical Contaminants
Identifying
Contaminants
Spectrographic
Analysis
Particle Count
ISO Codes
The Effects of Contamination
Contaminants
and Their Effect in Component Wear
Effect Of Dirt (Silicon)
Effect of Water (Sodium)
Contamination Prevention
During
Manufacture
During Equipment Operation
During Oil Storage,
Fill, and Change
During
General Maintenance
Summary
Contaminants in hydraulic system are things foreign in the system - things that do not belong there. There are two types of contaminants: Particulate and Chemical.
Particulate contaminants are the most common, measurable and controllable. Particulates can originate inside or outside hydraulic systems. Metal particles resulting from component wear are generated inside the system. Dirt, sand, rag fibers, etc. are contaminants that invade the system from the outside. Contaminants accelerate wear and multiply as they move through hydraulic systems. Abrasion, fatigue and silting are three ways that particulate contaminants can rob efficiency and performance from hydraulic Systems.
Abrasion:
Abrasive particles scrape metal from hydraulic
components. Wear metal is created, multiplies, and travels to other parts of the
system for more damage.
Fatigue:
Repeated high-pressure stress loads cause metal to chip or break from components
and contaminate.
Silting:
Small particles build up on metal surfaces and clog
the flow of fluids. The result is jamming and sticking between valve components
and reduced system efficiency.
Chemical contaminants can also originate inside or outside hydraulic systems. They include heat, water and air. These contaminants breakdown the oil's chemical composition, produce other contaminants in the form of oxidation and acids.
There are two methods of identifying particles or contaminants in hydraulic oil, Spectrographic analysis and particle count
Spectrographic analysis identifies and quantifies the elemental constituents present in the oil in parts per million, i.e. metals and alloys which are about 10 to 15 microns in size.
Particle count can quantify any type of particle, metal & nonmetal, from one micron to 200 microns in size. Particle count is reported in the number and volume of fluid. It is reported as the number of particles greater than a certain size.
The International Standard Organization (ISO) has established codes to quantify particulate matter by size.
The governing ISO standard, ISO 4406, establishes a two-factor code (Y/Z) to express fluid cleanliness. The first factor (Y) represents the number of particles larger than 5 micron and the second one (7) stands for the number of particles larger than 15 micron. The 5 and 15-micron ranges are selected as they can indicate presence of rapid wear and potential early failure.
Contaminants, when present in a system, reduce system efficiency, accelerate component wear, bring slower performance, lower productivity, higher operating cost, and lead to major break down.
The effects of contamination, however, are often difficult to detect because efficiency losses occur slowly over time. These invisible efficiency losses, however, have a huge impact on operating costs.
Contaminants and Their Effect in Component Wear
The tables below give the result of oil analysis carried out on samples taken from hydraulic systems of different machines. There is also an analysis result of new oil for comparison purpose.
The analysis is done using the atomic the oil absorption spectrophotometer, which is the equipment used for spectrographic analysis. The result indicates the level of wear particles in parts per million (PPM).
Table 3.1: Oil analysis result of new and used oil samples.
| Si | Na | Fe | Cu | Al | Cr | |
| Source | PPM | |||||
| New Oil | 0 | 1 | 0.9 | 0.7 | 1 | 0.7 |
| Excavator | 9 | 5 | 5 | 3 | 0 | 2 |
| Dozer | 21 | 11 | 10 | 8 | 10 | 2 |
| Loader | 10 | 29 | 31 | 28 | 1 | 2 |
| Dozer | 3 | 4 | 5 | 4 | 1 | 1 |
Elements Analyzed:
The elements analyzed are those, which are the main constituents of the hydraulic component parts and also contaminants.
Silicon (Si) in Oil indicates the presence of dirt. Sodium (Na) is an indication of the presence of water in the system.
The levels of iron (Fe), copper (Cu), aluminum (Al), and chromium (Cr) in the system indicate the extent of wear in the hydraulic component parts like pumps, motors and cylinders.
Copper indicates wear of pump bushings, end plates, slippers and port plates, based on the type of pumps installed in the system.
Iron and aluminum indicate pump and cylinder wear.
Chromium indicates wear on cylinder rod coating and pump rings.
We will analyze Table 3.1 above taking two results that have high level of silicon compared to sodium to see the effect of dirt on the wear of components
Table 3.2
| Si | Na | Fe | Cu | Al | Cr | |
| Source | PPM | |||||
| Excavator | 9 | 5 | 5 | 3 | 0 | 2 |
| Dozer | 21 | 11 | 10 | 8 | 10 | 2 |
Both results of the above samples indicate the presence of dirt, which is shown by the level of silicon.
They also indicate the presence of water that is shown by the level of sodium.
The other elements show the level of wear metals in the system.
As can be seen from Table 3.2, the level of silicon is high in both samples compared to the level of sodium. Silicon, however, is higher in the sample taken from the dozer compared to that of the excavator.
It can also be observed from the table and the graph that the higher the level of contaminants, the higher the level of wear on the component parts as shown by the higher level of iron, copper and aluminum.
The levels of contaminants are observed to be low for the excavator. Consequently, the wear level on the components is low.
Effect of Water (Sodium)
The table below, Table 3.3, shows the analysis result of two samples taken from a wheel loader and a dozer hydraulic system.
Table 3.3
| Na | Si | Fe | Cu | Al | Cr | |
| Source | PPM | |||||
| Loader | 10 | 29 | 31 | 28 | 1 | 2 |
| Dozer | 3 | 4 | 5 | 4 | 1 | 1 |
Here, the higher level of contaminant is water, which is indicated by the level of sodium. It is observed that even though the level of dirt or silicon is low, the level of wear of the loader’s hydraulic components is high due to the presence of water.
The result for the dozer indicates low level of Na and Si and as a result the level of wear is also low. The above results, therefore, indicate how contaminants increase internal wear hence producing internal contamination, which would finally lead to component breakdown.
It can also be deduced that dirt is not the only contaminant that causes component wear, contaminants like water can also be the cause of internal wear and component break downs.
Hydraulic systems are exposed to contamination:
Contamination control is quality control. It can be prevented at different levels.
Contaminants can enter hydraulic systems during manufacturing. Manufacturers should et their own hydraulic system cleanliness targets for equipment and components leaving their plants.
A variety of contaminants can be introduced during operation. The important methods of avoiding these contaminants from entering the system are through:
Avoiding leakages
If oil can go out, then there is high possibility that dirt can go in. Therefore, performing daily inspections and fixing leaks immediately is very important.
Keeping hydraulic tanks filled to the appropriate level
Insufficient fluid levels are a leading cause of pump cavitations, leading to pump failure and contamination of the entire system.
Low oil level can also result in high oil temperature, causing oil degradation.
Monitoring hydraulic system temperature
Excessive heat in the hydraulic systems thins the oil, increases fluid oxidation, bakes seals, and blisters hoses. The above problems will then lead to wear and internal contamination of the system. It is, therefore, important to monitor system temperatures and, if equipped, watch temperature gauges and sensor lights.
Maintaining valves
Hydraulic systems should operate with-in the designed system pressures. Low relief valve settings could lead to system overheating and thus wear and contamination. Relief valve settings should, therefore, be within manufacturers' specification.
During Oil Storage, Fill, and Change
Selecting the right oil
High quality hydraulic oils contain additives like oxidation and foam inhibitors that help prevent contamination. The higher the zinc level (an anti-wear agent), the slower the wear rate.
Therefore, selecting the proper and recommended oil is important.
Filtering oil when filling
Oil is refined and blended under relatively clean conditions, but even new oil can contain thousands of microscopic particles. Oil picks up contaminants if it is stored in dirty containers, filled in through dirty funnels or transferred through dirty lines. Filtering oil with external filtering equipment, whenever we fill oil, is the best way to avoid contaminants entering with the oil into the system.
Changing oil regularly and properly
Changing oil using the manufacturer’s recommendation should be followed. Monitoring and evaluating the oil condition and the contaminants level inside the oil will also guide in establishing proper oil change or cleaning interval.
Usage of the correct type of filter and changing filters regularly is also important.
Contaminants can enter a hydraulic system any time it is open, whether it is when replacing filters, or repairing a major component.
To prevent contamination, one should:
Hydraulic system maintenance starts from knowing what is in your equipment hydraulic systems.
Today’s machineries do not tolerate dirt and other contaminants as their predecessors did.
Contamination control is the prevention for most of hydraulic system problems observed today.
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