Oil Cleanliness: The Key To Equipment Reliability

EP Editorial Staff | January 1, 2008

Part I of this three-part series covered basic filtration principles and how to measure fluid cleanliness using the ISO 4406 chart. Part II focused on filter placement and setting cleanliness codes to maximize equipment reliability. In this concluding installment, the author discusses setting up a cleanliness program to maximize equipment reliability.


As noted in the two prior installments of this series, we most often think of the importance of fluid cleanliness in the context of hydraulic systems and their very sensitive components. Referring to Fig. 1, it’s clear to see there are many ways that solid contaminants can enter a typical hydraulic system:

  • Built-in contaminants, which occur in all new systems, are caused by debris from the construction of the equipment. The removal of these contaminants is through flushing until an ISO Cleanliness Code two levels below the established code for the equipment is achieved. (See Part II of this series, pgs. 8-12, LUBRICATION MANAGEMENT & TECHNOLOGY, November/December 2007, to learn how cleanliness codes are established.)
  • Generated contaminants occur primarily from the wearing of components in the hydraulic pump, but also can occur from cylinder and valve wear. These contaminants are removed through proper filtration.
  • Ingression of contaminants occurs when contaminants enter from the outside. This begins with the addition of new oil, which, if unfiltered, is not clean enough for the system. Most new oils introduced in bulk from steel drums normally exceed the cleanliness requirements of the system.
  • The cleanliness range of new oils is highly variable, but normally they have an ISO Cleanliness Code exceeding 22/20/18. The only exception is the introduction of oil filtered in a plastic drum to a certain cleanliness code, such as 15/13/11, and added in a way to minimize ingression from the outside. Therefore, if hydraulic oils are not purchased to a guaranteed cleanliness, they must be filtered during addition. A good practice is to filter all oils with the use of a filter cart.
  • The primary ingression of particles is from the outside through vents and cylinder rod packing. The key to fluid cleanliness is to be proactive by keeping ingression to a minimum by adding clean oil with the use of best practices to keep outside particles from entering, utilizing good desiccant breathers on vents that can filter down to 2 microns and maintaining proper sealing and packing in cylinder rods.

Remaining particles need to be removed with an effective filtration system. Remember, it has been estimated that the cost to remove particles by filtration is five to 10 times greater than proactively keeping the contaminants from entering.


Steps in a fluid cleanliness program 
A best-of-class fluid cleanliness program involves the following steps:

1. Analyze the system… 
Gather data on the specific equipment, such as operating conditions, criticality, OEM recommendations, type of fluid and usage, downtime and repair costs and historical and current data on fluid cleanliness and wear particles. Utilize both onsite testing, such as the patch test, and outside oil analysis for particle counts and wear debris along with fluid condition.

2. Establish performance and operational targets…
Utilize OEM recommendations and industry standards to establish ISO Cleanliness Targets for each piece of equipment in the program. Compare target ISO cleanliness codes with current ISO fluid cleanliness.

3. Implement plan for target achievement…
Consult with filter manufacturer for the most cost effective program utilizing optimum filtration equipment and placement to achieve established objectives.

Proactively implement the program to minimize particle ingression in the system. Estimate return on investment by comparing current program costs with proposed future costs, by evaluating current and future fluid costs, production downtime costs and repair costs (including parts and labor).

Establish a monitoring program in both frequency and types of tests. Implement oil analysis monitoring of fluid cleanliness, wear debris and fluid condition. Utilize, where appropriate, onsite testing, such as online and portable particle counters and filter patch testing. Work closely with the selected oil analysis laboratory and filter supplier to achieve the optimum monitoring program.

4. Monitor and adjust the program… 
Once the program is implemented, utilize the monitoring techniques to evaluate the results. Analyze data and compare to program objectives. Make adjustments, if necessary, to achieve objectives. Continue monitoring to keep the program on track and recalculate return on investment to demonstrate program success to management.

Real-world successes 
Until now, the discussion in this installment of our cleanliness series has focused on hydraulic systems. There are, however, benefits for all lubricating systems where fluid cleanliness principles are followed. For example, circulating systems can utilize full-flow filtration on the fluid circulating line. Moreover, offline filtration can be utilized on reservoirs.

There is a misconception that clean oil is not important in gearboxes. While the cleanliness level is more stringent for hydraulic systems, clean oil in gearboxes is very important in the life extension of equipment.

The following case histories, on both static and mobile hydraulic systems and two gearboxes, show the importance of clean oil in equipment reliability.

Case history #1: hydraulic shear

A 1300-ton hydraulic shear used in a metal scrap yard in a harsh environment was experiencing severe pump problems. This dramatically affected production and led to the running of two shifts to meet production demands.

The system consisted of two 2400-gallon hydraulic oil reservoirs feeding 12 vane pumps at 3000 psig with solenoid control valves. Low quality remanufactured pumps were used and frequent pump failures occurred. Poor maintenance practices were a fact of life here, including: inadequate filtration utilizing a return line spin on 25µ nominal filter; recycling of leaked fluid without proper conditioning; the permitting of excessive leaks; use of low-quality hydraulic fluid; and no effective preventive maintenance.

Program implementation… 
The following changes were made systematically:

  • Existing oil was replaced with a higherquality ISO 68 hydraulic fluid.
  • Recycling of used oil was discontinued.
  • An oil analysis program was implemented to monitor fluid and equipment condition.
  • A fluid cleanliness target was changed from ISO 27/23/21 to ISO 17/15/12.
  • OEM-approved pump replacements were used.
  • Reservoirs were drained and cleaned.
  • Reservoirs were sealed to prevent particle ingression.
  • Practices to minimize leaks were implemented.
  • Proper filtration was implemented by replacing the return line filter with an offline ß3 = 200 absolute filter.

Results and conclusions…

  • ISO cleanliness level went from 27/23/21 to 14/12/10 in 24 hours after system was started with all the major changes.
  • Maintenance and operating costs dropped from $80,000/month to $20,000/month over an eightmonth period.
  • Production increased over the same eight-month period from 800 tons/day to 3200 tons/day. This resulted in elimination of one of the shifts, yet still allowed for the meeting of production demands.
  • Pumps were examined after a twoyear period and exhibited negligible wear.
  • This project demonstrated that significant results can be achieved quickly with the right program.
  • The project also demonstrated that an effective program involves more than just installing a filtration system. A total systems approach is important.

Case history 2: coal pulverizer gearbox

Coal fired power plants typically operate ball or coal pulverizers (as shown in Fig. 2) to crush coal to an optimum size for combustion. The crushers have gearboxes that run these mills, which are usually worm gears. Normally, they are lubricated with an ISO compounded mineral oil or a synthetic PAO or PAG.

The plant in this case study had six ball mills. None of the gearbox oil was filtered. Each gearbox contained 250 gallons of oil. This oil was changed on a time basis—usually every eight months—resulting in a total cost of $25,000/yr. for all six pulverizers. The major cost, though, was with equipment failure. A worm gear rebuild could cost $600,000.

0208_oilclean_fig2Program implementation…

  • Desiccant breathers were installed on all vents in the gearboxes to eliminate the ingression of coal dust.
  • An oil analysis program was implemented to monitor oil and equipment condition.
  • Oil change intervals based on oil condition as opposed to the previously time-based intervals were developed.
  • Mineral oil was replaced with a synthetic PAO.
  • A dedicated offline filter system that would run continuously during operation was installed for each individual gearbox. Auxiliary fill ports were added to the gearboxes, allowing for the filtering of new oil through the filtration system. Oil collection ports were installed before and after the filters to measure filter performance.
  • Testing was conducted on several units to monitor effectiveness of routinely using a filter cart for oil conditioning.
  • An ISO fluid cleanliness code of 16/13 was established; only a two-number code was used, measuring particles = 6µ and =14µ.

Results and conclusions…

  • Synthetic oil was added and initial readings on oil cleanliness showed an average of 21/16 for all gearboxes. After 22 hours, the cleanliness level dropped to 16/11. After 76 days the cleanliness level was 13/11.
  • Filter carts were used to clean two gearboxes for two days. The oil achieved a cleanliness level of 18/12. Fortyeight hours after the filter cart was removed, the fluid cleanliness was measured at 20/15. This demonstrated that a permanent offline system is more effective and easier to monitor than intermittently using filter carts.
  • Based on conservative numbers, with minimal operating and investment costs, savings well in excess of $100,000/yr. on each gearbox could be projected. ? The project demonstrated that gear oils don’t need to be dirty. Equipment life is greatly extended by running clean oil.
  • The project also demonstrated that high-viscosity oils can be effectively filtered with the right system.

Case history 3: hydraulic excavating shovel

Mobile equipment in the mining industry operates in a very harsh environment where premature component failure due to contamination is common. This was the case with a hydraulic excavating shovel like the one shown in Fig. 3. In 27 months, four variable speed piston pumps on this shovel failed at a cost of $20,000 each, along with associated hose, drive motor and servo failures. The oil life as a result of oxidation and contamination was only 2250 hours. Shovel downtime over the period was 39 hours valued at $26,000 per hour. Fluid cleanliness was typically at an ISO cleanliness code of 22/20/17. The goal was to increase equipment reliability through contamination control.

Program implementation…

  • Maintenance practices were implemented to minimize contamination ingression by cleaning and capping all the hoses during storage and installation.
  • Original hydraulic fluid rated at 4000 hours and showing signs of oxidation at 1000 hours was replaced with a higher quality fluid.
  • A cleanliness target of 15/13/10 was established. The strategy was to flush the system and filter with a ß12[c] > 1000 glass media filter replacing the original 10 micron nominally rated cellulose filter (ß10 = 1.4) to achieve the target cleanliness level and stabilize the system. This filter was replaced with a ß7[c] >1000 filter to maintain the target cleanliness code.
  • Improvements were made in applying better sealing for the elements and a flow deflector was installed to protect the element during service.

0208_oilclean_fig3Oil analysis sampling was standardized to the proper techniques and frequency. Training was provided to implement these new procedures.

Results and conclusions…

  • The cleanliness level of 15/12/9 exceeded the target cleanliness level.
  • Copper levels indicative of piston pump shoe dropped 70% along with other wear component metals.
  • After the cleanliness of the system equilibrated, the filter element replacement level increased from 500 to 1000 hours.
  • Over the next four years, there were no pump failures and shovel unplanned downtime was eliminated. Savings of nearly $350,000 vs. the initial failures over a 27-month initial period were achieved.
  • The fluid life was extended to 17,000 hours, greatly exceeding the OEM-rated fluid life of 4000 hours.
  • Practices were implemented to reduce particle ingression through the hoses, improving the filtration system. This resulted in significantly improved shovel reliability.


Before embarking on an oil cleanliness program, thoroughly evaluate your present situation and set reasonable objectives. Utilize filter companies and outside consultants to assist when needed. Be committed to the program long-term and the economic rewards will be significant. This was illustrated with the three case histories in this article. These are just the tip of the iceberg, however. There are many more real-world success stories that could have been presented to show the economic and reliability benefits of an oil cleanliness program

Do not expect to enhance equipment reliability through clean oil by merely improving filtration equipment. True and lasting success involves a total systems approach, starting with identifying sources of particle ingression and correcting the sources of entry.

Gearboxes don’t need to be dirty. There is a great economic incentive to filter oil in gearboxes, especially in harsh environments. Filtration is not limited to oils with ISO viscosities less than 100. High-viscosity gearbox oils (ISO 460) can be effectively filtered with present technology.


The author wishes to thank Aaron Hoeg of HY-PRO and Mike Boyd of Fluid Solutions for providing case history information and ongoing support in the research and preparation of this article.

Contributing editor Ray Thibault is based in Cypress (Houston), TX. An STLE-Certified Lubrication Specialist and Oil Monitoring Analyst, he conducts extensive training in a number of industries. E-mail: rlthibault@msn.com; or telephone: (281) 257-1526.



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