Hydraulic Oil; Keep it Clean - Keep it Cool - The International Association of Foundation Drilling

Hydraulic Oil; Keep it Clean - Keep it Cool
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Hydraulic Oil; Keep it Clean – Keep it Cool

by Tony Kraut, Branch Manager,
Bauer Equipment USA,
McKinney, Texas

Tony Kraut, a member of the ADSC’s Board of Directors and Chairman of the ADSC’s Education Committee, is the lead instructor for the ADSC’s Mobile Hydraulics Course. His many years of experience working with hydraulics is evident in this practical article especially geared to our Category III and IV Contractor Members. (Editor)

One of the most important requirements to consider for optimum operation of any hydraulic system is quality and cleanliness of the hydraulic oil. Permitting the ingestion of and allowing the existence of contamination in a hydraulic system affects the efficiency of the oil, damages seals and accelerates the wear of system components.

The hydraulic oil serves many purposes in fluid power systems. Its primary purpose is to work as a power transmission medium from the hydraulic pump to the actuator. This was explained in detail in the November 2003 issue of Foundation Drilling magazine. This power transmission uses the pressure and flow of the hydraulic oil to determine actuator speed and force. The hydraulic oil has other advantages in our system also, such as, lubricating components, dissipating heat, carrying contamination back to the filters and it also provides proper sealing between close tolerance machine parts.

Hydraulic oils on the market are engineered and designed with additives to provide a long and healthy life to the components in our hydraulic systems. These additives include anti-wear and anti-corrosive agents, anti-oxidizers, metal deactivators, foam retardants, dispersants, detergents, emulsifiers, conditioners and additives which allow the oil to be compatible with components, seals and gaskets specifically used in a hydraulic system. Petroleum, vegetable, synthetic or phosphate based oils may have been specified for special machines or applications. It is very important to be certain of what type of oil is used in each machine.

Dirty oil is the most common cause of hydraulic component failure. Precision components are particularly susceptible to damage from residue and suspended contaminants. This contamination works as an abrasive against moving parts. This abrasive action may appear to be slight to the eye, but realize that at high pressure the abrasions have created an excessive internal leak path in the hydraulic system. Most hydraulic components are designed to permit a certain amount of internal leakage. Moving parts must be lubricated and internal leak paths are designed solely for this purpose. Internal leakage is not lost fluid. This fluid eventually returns to the reservoir through an external case drain or by the way of an internal passage in a component. Additional internal leakage occurs as a component begins to wear and clearance between parts increase. This increase in internal leakage can reduce the efficiency of a system by slowing down the work, reducing the lubricating ability of the oil, and also by generating excessive heat.

External leakage is an obvious loss of oil from the systems. This can be hazardous, expensive and will attract dust and dirt from the environment which affects the appearance and operation of our machinery. External leakage is lost oil that can not be reintroduced into the hydraulic system. Remember that the purpose of the oil is to transmit power, lubricate, dissipate heat and to carry the contaminants back to the reservoir. This lost oil is wasted oil that does not serve any purpose. Allowing a leak to persist will reduce the total volume of hydraulic oil in the machine. Operating at a low oil level runs the risk of more damage to the components by possibly introducing air into the systems or by allowing the oil temperature to become extreme. Lost oil must be replenished by clean oil. This means that we must open our systems to the environment to pour or pump fresh clean oil into the reservoir. We should always try to reduce exposure to the environment. By opening up our system, we will ingest some contamination. Dirt can also be ingested at the external leak point. If oil can leak out, then dirt can get in. Most people take little concern of this contamination because it is minor and is usually only very small particles. How small? Most of our filtering systems are typically rated to 40 microns. One micron is equal to one millionth of a meter or thirty-nine millionths of an inch. The average diameter of a grain of table salt is around 100 microns and the average diameter of a human hair is around 74 microns. The human eye can normally see the size of 40 microns. I found that as you get older the visual calibrator loses its accuracy. The most harmful contamination in a hydraulic system is normally below this 40 micron range. This, of course, means that contamination in a system can not be evaluated by visual inspection. It also means that these smaller particles have a greater degradation effect on our system components; this is because the clearances between moving parts range between 5 to 20 microns. When small contaminate particles are suspended in the oil, they can lodge themselves between these tight clearances. This effect can lead to abrasion, fatigue and adhesion which ultimately affect the operation of the component.

The chart on page 45 shows the results of a study conducted by M.I.T. They found that mechanical wear is responsible for 50% of all component surface degradation. The study also found that this surface degradation was responsible for 70% of over-all loss of machinery usefulness.

Hydraulic oil is available in varying viscosity ranges (thicknesses or pour point) to provide the optimum effects in a specific temperature environment. A fluid that flows easily has a low viscosity, if it has a difficulty to flow then the viscosity is high. Imagine the effect of the viscosity of oil in a system that is transported from a cold environment on one job to a hot environment on the next job. By running low viscosity oil in a hot environment, you will experience excessive internal leakage, erratic response, excessive wear of moving parts, and the pump efficiency will decrease. By using high viscosity oil in a cold environment, you would experience a high resistance to flow, an increase in power consumption due to friction, sluggish or slow operation of actuators, and possible aeration of the oil. Many of you who work in these extreme temperature ranges may have experienced one of these symptoms.

Allowing the hydraulic oil to reach extreme temperatures (over 200° F) affects the ability of the additives to perform their purpose. This is known as "oil breakdown." When this occurs, you run a high probability of corrosion, silting and oxidation of components. This, of course, generates even more contamination particles leading to accelerated component fatigue. Once hydraulic oil breaks down, it can not be used and must be replaced. This oil would have a burnt smell and discolored appearance.

The cooling of the oil is accomplished by the proper design of the reservoir and efficiency of the heat exchanger. A reservoir is designed to slow down the flow of the oil which removes air, heat and allows fine particles to settle from the systems. The heat is absorbed through the external walls of the reservoir. This is accomplished by designing baffles in the reservoir to ensure maximum exposure to the walls and to separate the return side of the reservoir from the inlet side. This is important for both reasons: heat dissipation and de-aeration, otherwise air bubbles in the oil can not settle out and could be drawn into the inlet side of the pump where cavitation could occur.

The heat exchanger is the other component which stabilizes the oil temperature. It works much like a radiator. A criss-cross of tubing connecting to fins made of aluminum works to transfer heat from the system to the environment by using a fan to increase the heat dissipation. If the spaces between the fins are restricted, then it will reduce this heat transfer ability. I see that on some rigs the space in front of the heat exchanger and radiator is a convenient place to store an extra spool of kelly cable, shovels, extra oil jugs and possibly rain gear. This greatly restricts the air flow through the heat exchanger even though it is down wind of the fan

Reservoirs and heat exchangers are unique to the industry of mobile construction equipment. In an industrial application, there is little limitation to the reservoir size. But on mobile equipment we manufacturers are restricted by size and weight limitations, knowing that the machine needs to be transportable. Therefore, we need to minimize the size of the reservoir and maximize the size of the heat exchanger to achieve the desired effect.

Hydraulic return line filters are typically located down stream of the heat exchanger and at the inlet of the reservoir. This location is engineered into the system so the filtering of the oil has the maximum effect. Cooler and slower flowing oil will suspend and trap more particulates when passing through the filter element. As mentioned, earlier filters are rated by micron size. This means that the filter will trap most contaminates at, and larger than, the specified micron size. There may be some misconception of this micron rating, because I used the words "most contaminants" rather than "all contaminants." The micron rating relates to particulate size and is not a measurement of the filters efficiency. The efficiency of the filter is measured by a beta ratio factor. The beta ratio of a filter is rated during a steady flow test by the count of upstream divided by the count of downstream contaminants of the selected particulate size. Example: A 40 micron filter with a beta ration of 2 means that if 200 particles at or larger than 40 microns are introduced to the filter, it would still allow 100 particles at or larger than 40 microns to pass through. This would be shown as ß4 0 =2 . A more efficient 40 micron filter would be one with a higher beta ratio number. A filter with a beta ratio of ß40=8 means that only 25 of the 200 particles 40 microns or larger are allowed to pass through. Many filter sales representatives like to show you an annual cost savings by purchasing their less expensive filters. Amazingly, even they may not be aware of the efficiency of their own filters. Be wise to this, a less expensive filter may, in fact, be more costly in the long-run.

The value of maintaining clean oil has extremely high paybacks when you think of the initial investment that you made to purchase the drill. How many years do you expect to operate this drill? What value do you rate it at for resale? Let’s also consider the effects of interruptions in your production schedule when you experience down time due to equipment failure. All of these can affect your firm’s bottom line profits. This can easily be controlled by increasing the concern and discipline of your mechanics, operators and crew on the importance of clean oil when working on or servicing any hydraulic system.

With the advancement of our industry also comes the advanced technology of the equipment we use to perform our task. Increasing the knowledge of your mechanics and operators about the hydraulic systems of the equipment will provide huge returns for your production schedule. This is, of course, done through related educational programs which has numerous benefits. An invaluable benefit is that it will instill some pride in your employees for your equipment, your company and the industry which we serve.

The next ADSC Mobile Hydraulic School is scheduled for June 17-18, 2005 at the Hammer and Steel facility in Hazelwood, Missouri. Contact Cindy Colao at the ADSC office to reserve a seat for this program.

A Mobile Hydraulic Mechanic Certification program is also available for those interested. Feel free to contact me (972/540-6361) for more information or details on this certification program. Let’s face it, having your employees certified in their specialty fields makes you as a contractor even more marketable to your customers.

Recommended Steps to
Maintain a Clean Hydraulic
System Include

Do not expose the hydraulic system to a dirty environment.
When adding clean oil ensure the container, funnel, pump and area around the reservoir is clean.
Use clean caps and plugs when replacing hydraulic hoses. Do not leave the system open.
Ensure new hoses are thoroughly clean before installing them.
Don’t tolerate hydraulic leaks. Repair them ASAP.
Repair leaking hydraulic cylinders and other components.
Change hydraulic filters at manufacturers recommended intervals.
Have an oil analysis preformed on your oil every two years or whenever you suspect a contamination problem.
Drain the hydraulic systems, clean the reservoir and replace with clean oil every five-six years or when ever a catastrophic failure has occurred.
Keep the oil level up in the hydraulic reservoir.
Don’t mix different oil bases. Ensure when adding oil that it is compatible with the oil currently in the system.
Do not allow the oil to reach extreme temperatures (above 190-200° F).
Don’t ignore poor response or operation problems (intermittent or constant).

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