Hydraulic System Leakage - The Destructive Drip

Lloyd Leugner
Tags: hydraulics

A single hydraulic leak of one drop per second is equal to 420 gallons of oil in a 12 month period. This volume adds up fast. It has been estimated that over 100 million gallons of fluids could be saved every year in North America if external leakage from hydraulic machinery and other lubricated equipment was eliminated.

In Canada alone, over 12 million gallons of oil is wasted due to leakage. In economic terms the cost of this waste is staggering. Besides high oil consumption, the economic effects of hydraulic system leakage include inefficient machinery operation, environmental damage, safety and accident liability, premature machine component failure, poor manufacturing quality and increased capital costs.

The Effects of Leaks

Several years ago, Mobil Oil Corporation completed a study in the U.S. that compared hydraulic reservoir oil capacity to actual oil consumption. The study resulted in the development of Mobil’s Hydraulic Fluid Index (HFI) which concluded that in the United States the national HFI average is 4. This means that every year in the U.S., the average plant uses four times more oil than it’s machines actually hold!

Let’s assume conservatively that one half of the 100 million gallons of lost lubricants previously described are hydraulic fluids. Assuming that the average cost of replacing these hydraulic fluids is $5.00 per gallon, the resulting direct cost in replacement lubricants alone is $250 million dollars!

A very high percentage of manufacturing plant and industrial facility managers mistakenly assume that if the hydraulic machinery is available and working, it is operating satisfactorily. This assumption is a serious and costly mistake. What these managers fail to consider is whether or not the hydraulic machinery is actually operating at it’s maximum “performance efficiency.”

The strategy of Total Productive Maintenance calls for a world class goal in which the Overall Equipment Effectiveness (OEE) of machinery should be at least 85%, where availability should equal 90%, performance efficiency should equal 95% and the quality rate should be at 99%.

If the hydraulic equipment has a leak (either internal or external), the performance efficiency will be directly (and dramatically) affected. For example, if the designed cycle time of an hydraulic circuit is 3 seconds, but the leakage causes the cycle time to slow to 6 seconds, the result will be reduction in performance efficiency of 50%.

If there are several hydraulic leaks on the machine, the performance efficiency can be reduced even more dramatically, which in turn will affect the overall effectiveness of the machine. Most process plants and manufacturing facilities in North America have OEE’s in the range of 30-50% even though the measured availability is 90% or higher! In hydraulic machinery, the primary cause of reduced performance efficiency is often internal or external fluid leakage.

Approximately 15 million gallons of hydraulic fluids are used annually for industrial applications in Canada alone. Recent environmental studies show that a portion of this leaked fluid ends up in ground water, rivers, lakes, and in the soil itself, causing untold damage to the environment, fish and wildlife.

Internationally, the marine, forestry, mining and agricultural industries in particular are responsible for much of the environmental damage and the resulting high cost of cleanup, much of which goes unreported and ignored. Sadly, only incidents like the catastrophic spill caused by the Exxon Valdez receives much attention. In fact, the overall environmental damage caused by cumulative hydraulic oil leaks worldwide should be of far greater concern to environmentalists and industry than that which is caused by a marine tanker leak.

Every day in North America, a machine operator or technician slips and falls on the remnants of a leaking hydraulic system. This fall costs an average of $200.00 per incident in lost wages alone. If we calculate interruptions to production, workers compensation costs, medical costs and the costs associated with lawsuits that may result, the cost per incident escalates dramatically.

Likewise, pressurized hydraulic fluid presents a considerable fire risk whenever threaded pipe connectors, valve seals and flexible hoses rupture or vibrate loose. This risk is especially high when the machine operates in an environment where ignition sources are constantly present, such as plastics forming, die casting, etc.

Petroleum-based fluids present the highest risk for fire. High-pressure leakage often produces an atomized spray, or mist, that might extend up to 40 feet. Exposure to a hot surface could ignite this rich mixture of oil and air, producing a torch-like flame.

While more work needs to be directed at quantifying the risks of fire in hydraulic applications, some risk is always present where there is uncontrolled liquid hydrocarbons in the presence of oxygen and hot surfaces. This condition is descriptive of most plant environments where hydraulic machines are used, so the risk should not be taken lightly.

It is a statistical fact that 80% of machine and equipment stoppages and component failures are caused by contaminated lubricants. Many of these contaminated fluids are a direct result of fluid leaks from hydraulic machinery. Simply stated, if the oil can leak out past the seal, contaminants in the form of dust, dirt, water and chemicals can enter the lubrication system, causing increased rates of wear through abrasion, scoring of moving parts, adhesion, fatigue and corrosion.

Think of a hydraulic cylinder rod extending under pressure. As the rod extends, oil leaks past the seal. As the rod retracts, contaminants will stick to the oil film on the rod like fly-paper and is drawn into the system The same is true of the shafts on hydraulic pumps and other rotating equipment. As the oil leaks past the seal, contaminants can enter the pump along the shaft past the seal causing the system to become contaminated.

Depending upon the design of the cylinder or the pump, the overall cleanliness of the plant itself and the extent of the leak, the hydraulic system can become excessively contaminated within months, weeks or even hours and the process of premature system failure has begun.

Once the hydraulic system becomes contaminated with dust and dirt, which might enter the system past leaking seals, another severe problem can develop which can directly affect the quality of manufacture. Much of today’s hydraulic machinery is controlled by electrohydraulic servo-valves that are extremely sensitive to contaminants in the hydraulic fluid.

The contamination will cause servo valves to stick or operate erratically, which in turn can affect the accuracy of the process, or the dimensions of the products being manufactured. The result will be a manufacturing process which increases its production of items which do not meet specifications and are in fact waste.

This is directly related to the machine’s overall equipment effectiveness formula that was previously discussed. In other words, the hydraulic leak causes fluid contamination, which in turn causes hydraulic controls to operate erratically, which in turn can cause poor manufacturing quality or cause an increase in scrap, which, eventually, results in tremendous financial losses

This is the primary reason why manufacturing facilities and process plants must consider hydraulic leaks as a direct economic concern and explains why the calculation of the “overall equipment effectiveness” formula must be applied consistently to improve machinery reliability. It is essential for the economic survival of our industrial facilities.

Every one of the effects of hydraulic leakage outlined above can increase the frequency with which a manufacturing plant or facility must prematurely purchase new equipment. The life cycle of equipment can be extended significantly if the increased rates of wear and corresponding reduced reliability are reduced by effectively eliminating, or at the very least, managing hydraulic system leakage.

Obviously, a discussion of the effects of hydraulic system leakage cannot be complete unless we consider the following questions; “What are the primary causes of these costly leaks and how can they be prevented?”

The American Society of Mechanical Engineers (ASME) has indicated that there are over 48,000 differing sealing compounds, composites and combinations of corrosive elements which can affect the life and operation of rubber and other elastomeric seal materials.

It is, therefore, critical that the initial machine sealing design and seal selection is well thought out and considers such things as fluid and seal compatibility, shaft run-out, shaft and cylinder rod finish, operating temperatures, pressure ratings, flow rates, acceptable contamination limits, servo-valve and pump clearance specifications, and any other system design criteria which may affect the tendency of an hydraulic machine to leak.

Proper maintenance includes correct alignment of hydraulic pump drive shafts with electric motors or pulleys, as well as correct alignment of cylinder rods, to insure that side loading does not occur. Regular monitoring of hydraulic oil temperature is also essential. Hydraulic fluid temperature should be kept as cool as possible, but an acceptable operating range is 120° - 140°F.

Hoses and fittings must be inspected regularly to ensure that they are free of leaks and the hoses themselves should be inspected for cracks and blisters, indicating overheating or incompatibility conditions. Above all, filters must be selected carefully and serviced regularly, while the machinery itself must be kept scrupulously clean.

Oxidation caused by overheating and contamination by dirt, water and wear metals are two of the biggest causes of hydraulic system failure and can lead directly to leakage problems. Hydraulic lubricant systems should be monitored at least once every three months for viscosity, water content and spectroscopic wear levels. In addition, contamination levels must be monitored using electronic particle count analyses.

These results should be compared to targets using the International Organization for Standards Cleanliness Code 4406. It is recommended that contaminant sensitive, servo control systems in laboratory, aerospace, mechatronic and robotic systems maintain a cleanliness level of 13/9 (15/13/9 under the revised ISO 4406 standard), while machine tool and hydrostatic systems with pressures exceeding 4500 PSI maintain cleanliness levels of 14/11 (16/14/11 under the revised ISO 4406 standard).

When these contamination levels are exceeded, evaluate the filtration system and flush thoroughly. (See Section 25 of “The Practical Handbook of Lubrication” for recommended oil analyses test requirements and standards).

To conclude, hydraulic leaks cost our industrial community millions of dollars annually and the biggest single problem associated with this phenomenon is the fact that our industrial plant management considers that this waste is normal. It is not!