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:
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.
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.
The following changes were made systematically:
Results and conclusions…
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.
Results and conclusions…
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.
Oil analysis sampling was standardized to the proper techniques and frequency. Training was provided to implement these new procedures.
Results and conclusions…
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.