Avoiding Code Blue: The Care and Feeding of Hydraulic Systems

May 1, 2000
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In a cardiac unit of a hospital, Code Blue means that someone’s hydraulic system is failing. Time is of the essence in resuscitating the human body’s pump, otherwise the end is near. While the failure of an excavator’s hydraulic system does not have the emotional cost of a heart attack, the untimely death of a machine from hydraulic failure can hinder your ability to get the job done, thus affecting your company’s financial health.

The comparison of a hydraulic system to the circulatory system of the human body is not that great a stretch, according to Steven Braun, an instructor at the John Deere Training Center in Davenport, IA. “If you looked at a hydraulic system on most any piece of equipment, the heart of the system is the hydraulic pump,” he states. “The hydraulic oil is the blood of the system. The arteries and capillaries of the human body would equate to the hoses and connections of our machine’s hydraulic system. The muscles of our machine would be our cylinders or the hydraulic motors that we turn with the hydraulic oil.”

Abuses to both the human body and a machine can result in short- and long-term consequences, rendering both incapable of performing any work. Contaminants can plug openings, causing the system to work harder and increasing the heat load on the critical components. Abrasives can erode seals and valves, creating leakage and reducing the efficiency of the machine. The wrong fluids can break down under working pressures, leading to massive failures of all components.

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A Proper Diet

There are basically two types of hydraulic systems: open- and closed-center systems. “An open-center system is one in which hydraulic fluid circulates through the machine all the time,” describes David Moorman, sales manager for Burlington Installation Company in Wichita, KS. “It goes through the valves and then back to the tank where itís picked up by the pump and sent back through so itís constantly circulating. A gear pump is an open-center system. In a closed-center, or pressure-flow compensated, system the pump actually destrokes. When they’re not in use, there’s very little fluid going through any of the valves. Typically, a closed-center system is a closer tolerance system used in high-horsepower attachments and equipment such as scrapers, graders, or excavators that typically run pressures over 3,000 psi. Those are piston pump systems and are much more susceptible to contamination. Consequently, the breakdown costs are going to be a lot more because the components are a lot more expensive. The complexity and the repair costs all escalate as system operating pressure goes up.”

The best engineering in the world won’t survive very long if you feed your machine the wrong diet. All manufacturers design their machines to use hydraulic fluids that have certain properties, including heat range, viscosity, and lubrication ability. “Following the guidelines in the operator’s manual is probably the most important thing,” points out John Strangberg, service marketing manager with Case Corporation in Racine, WI. “Follow that to the letter and, more importantly, only use approved lubricants and filters. Many of our machines have a common reservoir between the hydraulic system and transmission cases. Many times a hydraulic fluid from a local supplier wonít have the right blend of additives that is needed. Using the approved lubricants is very important for taking care of all the requirements in that particular compartment.”

Lubricants fall into a variety of classes and are usually determined by use or additives in the oil. These may include antiwear-type hydraulic oils. Another class is rust- and oxidation-inhibited (R&O) oils, meaning they do not possess an antiwear quality. Some hydraulic systems might not need this ability. Turbine-grade oils have an enhanced additive package to provide longer life by protecting against breakdown caused by heat and moisture that might be present in a turbine application. Recirculating oils do not possess great amounts of additives.

The type of pump used in the machine often determines the type of fluid used, explains Wayne Marinclin, manager of technical services for Pennzoil Products in Johnstown, PA. “The real defining entity in hydraulic systems that determines what kind of oil you’íre going to use is the pump. If you have a vane-type pump, you’re going to use an antiwear hydraulic oil. If you have a piston or diaphragm pump, you could get by easily with R&O oil. There’s no need to have the antiwear or zinc compound in there for that purpose.”

Most purveyors of hydraulic oils have a good knowledge of the various equipment, so if the machineís operating manual has long since vanished, a quick call can help identify the proper fluid type. “Many times what happens is owners lose or misplace the manuals or the piece of equipment has changed hands several times,” observes Marinclin. “By asking about the design of this system—specifically the pump—you can find out what kind of fluid to use. A contractor probably would not know that, but the information should be available if it’s a new piece of equipment in the manufacturerís manual. If the specification is not there, then he has to rely on people in the industry who would know which questions to ask about the equipment and then deduce what product to use.”

The Daily Checkout

One of the most important procedures is the daily inspection of the machine by the operator prior to performing any work. This should include checking all fluid levels, as well as piping, hoses, fittings, and all surfaces for possible hydraulic-fluid leakage. A puddle under the equipment is an obvious sign of a problem. “Visual inspections by operators are very important,” Strangberg emphasizes. “Construction equipment is out in a pretty hazardous environment: cylinder rods get dented and hoses get snagged and ripped off in certain applications. For instance, if you see a cylinder rod that appears to be oily on the outside, it’s usually an indication that there’ís a shaft-seal or cylinder-seal problem. As the rod retracts, it’s also going to take some of that dirt back into the system. Even though not much oil appears to be leaking, those situations pull a lot of dirt back into the system.” Another area that should be inspected daily is the hydraulic reservoir breathers in the reservoir caps. These should be checked to ensure that they are in place and that the breathers are replaced at the right intervals. Failure to check these could allow dirt to enter the reservoir.

The cooling components of the machine should also be inspected daily to make certain that they are working properly and are not inhibited by excessive dirt or debris. “One of the things that directly shortens the life is not maintaining your cooling system,” notes Braun. “If the hydraulic fluid is overheated, its lubrication capabilities are reduced. It is important to maintain the cooling system. They’re designed and sized appropriately, but they’re designed and sized to be kept clean. If you think of the hydraulic system as the lifeline of your machine, you want to maintain your cooling. You want to maintain your lubrication capability; therefore you transfer power efficiently.”

Dirt is the greatest problem in a hydraulic system. “These machines donít make money sitting still,” says Marinclin. “If they have a leak that establishes itself before the operator gets a chance to take it down, they’re content to just put fluid in it. Now, there’s nothing wrong with putting fluid in. It’s going to leak out faster than normal if there’s a bad seal. They’ve got to be careful that they at least put the fluid in under somewhat clean conditions. It wouldn’t be unusual for somebody to bring out a pail that has some dirt on it and just sort of blow it off, open up the bung, and dump it in. You’re going to dump some contaminants in there. Those contaminants act like an abrasive, and if they get to the pump and it’s a vane pump, you’ll get accelerated wear.”

Internal wear of components can also contaminate a system. “A pump that’ís beginning to wear will put metal particulates into a hydraulic system, and then we get into what we call a catastrophic failure,” says Braun. “We have one small component that fails, and the contamination from that failed spool or piston goes throughout our hydraulic system and starts cutting away cylinder seals and lines, gets into other control valves, and causes erratic operation of the machine.”

Some machines need to be stretched out before performing work, especially on cold days. In close-center systems, where the pump has a variable displacement and is near a zero displacement when the functions are all in neutral, the oil doesn’ít start circulating until a function is actuated. “System warm-up takes a little longer on these machines because the oil isnít running constantly,” states Strangberg. “It’s a good idea to cycle all the hydraulic functions without a load to adequately warm up the machine. Proper warm-up under no load is important to help extend the service life of the hydraulics.”

The operator should maintain vigilance during the day on the equipment. Depending on the working environment, a hose could snag and be torn open, resulting in a total loss of hydraulic fluids. If the operator continues to run the equipment without hydraulic fluids, damage might occur to the pump, including a condition known as cavitation in which the combination of heat and pressure creates pitting on the metal surfaces of the pump interior. “Obviously, you can fix the hose and put the oil back in, but if it was run very long or the pump is growling and making that crazy noise, there will probably be some internal damage,” Strangberg explains. “The operator has to be aware of any type of funny hydraulic noises or a loss of oil because of a hose failure. The machine should be shut down immediately.”

Preventive Maintenance

Just as an annual physical provides the opportunity to catch medical problems while they’íre small, preventive maintenance (PM) programs perform the same role for equipment. The primary activity performed during a maintenance interval is changing the filters and fluids so that the fluids are clean and perform up to specification. All manufacturers have recommended maintenance intervals, but a variety of factors may increase or decrease the maintenance intervals, such as the environment in which the machine operates and the amount of abuse the machine receives.

An effective PM inspection begins with a visual examination of the entire hydraulic system. “Walk the lines and make sure that you donít have any external leaks and that everything is tight,” recommends Braun. “Make sure that there is no room for dirt or other contaminants to get sucked into the system. Look for external cuts or pinch points that’ll create heat. An external cut will bring in outside contaminants.”

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Oil analysis can measure of the relative health of a machine and provide early detection of internal problems. “In severe applications, we recommend scheduled oil sampling,” says Strangberg. “Many times this can dictate that oil changes should be done sooner, but then again, at times it can also delay the drain of a hydraulic reservoir. If a lot of dirt is not ingressing back into the system and the oil is clean, there’s usually no need to change it. Scheduled oil sampling every 250 hours for the approximate $20 cost is cheap insurance, especially when you have these 60- to 80-gallon reservoirs. You can save a lot of the cost. You can also predict failures in hydraulic components by the particle count in the oil.”

Filters should be inspected as part of the PM program as well. A filter that is plugged with contaminants creates a pressure differential that can increase the heat load in the system and cause degradation of the hydraulic fluid. “Usually a filter will have a gauge on either side of it,” says Marinclin. “In the industry, they’ll do whatís called a ‘Delta P,’ a pressure differential across the filter. When that gets too high, you know the filterís plugging up; now youíve got to determine why is that happening. Is it due to outside contaminants such as dirt? Is it due to internal contaminants overheating the oil and destroying it chemically, causing it to form a deposit?”

Many companies offer comprehensive maintenance programs on their equipment. “Our dealers do offer a customized maintenance inspection,” Strangberg states. “They provide a package for 250 or 500 hours service [that includes] all the filters and lubricants required at that interval, along with the machine inspection. We encourage the customers to take advantage of these programs because that gets the machine into the dealership and inspected by a trained eye that sees this equipment day in and day out. Then the dealer can counsel that customer on little things that might need attention before they become major failures.”

Whether the contractor or the equipment manufacturer performs the maintenance on the machine, the critical thing is to be consistent. “If you want to maintain your systems in house, which any good contractor would want to do if he possibly could, first of all youíd have to have a full knowledge of the operator’s manual that’s provided with the machine,” recommends Braun. “Follow the periodic maintenance procedures. If somethingís going wrong, then Iím going to repair it prior to its failure. I’ím going to do it knowing that I’ím spending the money in the right place.” Braun says education and understanding a hydraulic system is essential to maintaining it. “I can’t think of one thing thatís really necessary other than knowledge. Knowledge of your hydraulic system is an essential tool to maintain your machine yourself. The contractor’s got to be disciplined and educated to change those filters, check the levels, and use high-quality recommended oils. Really, it’s as simple as that.”

A TIGHT Machine Is an Accurate Machine

An important function of a hydraulic system maintenance program is keeping the system operating tightly within specifications. With some of the advances in attachments designed to improve the accuracy of grading operations, this tightness can lead to greater productivity and less regrading.

Spectra Precision of Dayton, OH, markets sensor technologies that control the blades of the machine automatically in order to obtain a proper grade. The company started with laser-based reference systems, then moved to control systems that automatically raise and lower the cutting edge through electrohydraulics. The company has developed other sensor technology that uses global positioning systems or sonic devices that measure down to either a previous pass or string liner. A new product called BladePro 3D measures a variety of attributes, including the slope of a motor grader control blade, the direction of travel slope, the main fault slope, and the rotation of the blade. “You basically dial in a slope, and we leave the proper cross slope regardless of what the rest of the machine is doing,” states Rick Piekutowski, hydraulics designer with Spectra Precision. “With this system, it’s automatically adjusting the slope. Previously, the operator would’ve had to have stakes and been adjusting the slope as he went along. He would’ve had to reference something for an elevation, possibly a string line, or he could have been doing that manually to put in these type of shapes. This eliminates the need for any of the staking.”

Because of the automatic adjustments, a tight hydraulic system becomes critical to the successful use of this equipment. “You need a tight machine mechanically,” states Piekutowski. “All of the machine components have to be in spec [in terms of] looseness. When we move the cylinder, we’re counting on moving the cutting edge, and if there’s a lot of backlash or slop, you don’t get that instant motion, so it’s important that it’s tight mechanically. Hydraulically, we use proportional valves that require a little better filtration than did machines from 20 years ago. Fortunately, most machine manufacturers have improved their filtration over the years. What they’re requiring in their machines is much better quality oil than they used to have. It’s not longer just a simple paper cartridge, and if you couldn’t see the dirt in the oil, it was OK. This is very clean oil. They’re using load-sensing, pressure-compensated pumps, and they may have electrohydraulics on there as well.”

An aggressive maintenance program is critical to keep everything working as it should, states Piekutowski. In addition, quick-coupling systems used in the field may also create an entry point for dirt. Keeping the coupling systems clean should be mandatory. “If you’re opening and putting quicks back together, you’re going to put dirt in the system,” he says. “Some operators just don’t take the time to really clean that before they open it. In a lot of places, we’ll add a filter in front of our valve to protect it. Even though the machine has good filtration, there’s no way to keep them from putting some dirt into the system.” 

Pressure Cleaning

Even operators who are diligent about preventive maintenance might not realize that much of a hydraulic system’s internal contamination is present even before the system goes to work. Debris from manufacturing and packaging, as well as from cutting new hoses and crimping on the fittings, can contaminate a system before the fluid is added.

The Australian company Compri Technic Inc. manufactures the Contamination Elimination System, which uses a pneumatic launcher to force a polyurethane projectile through hydraulic hoses and tubes. The projectile-20% larger than the internal diameter of the hose-strips out contaminants.

“A lot of people are under the impression that since it’s a brand-new hose, it’s clean. That’s a fallacy. It’s really super filthy,” says Bruce Riley, who works for Compri Technic’s North American distributor in Bridgeton, NJ.

The CE System also cleans particles and residue from existing hydraulic systems without the repeated flushing that is usually required. For routine maintenance or after a pump or valve failure, disconnecting the ends of each hose and firing projectiles through each will remove contaminants. Compressed air or dry nitrogen (85-120 psi) acts as a propellant. Several projectiles may be needed for heavily contaminated hoses; three are recommended for new hoses. The whole process takes about 15 seconds per hose.

Sizing charts match up projectile sizes with hose sizes and fittings. “It’s virtually impossible for the projectile to become stuck or lodged in the hose” when the correct size is used, says Riley. One exception, he notes, is when the wire-braid hose has broken and is sticking through the interior wall of the hose. In this case, when a broken wire snags a projectile, the CE System becomes a diagnostic as well as a cleaning tool.