Hydraulic maintenance

A step-by step method to reduced maintenance and increased profit potential.

By Robert Lasky

The sole purpose of production equipment is to make a profit. To assure profitability, equipment must be kept in good running condition. It follows, then, that any maintenance performed must be directed toward this profit.

To correctly maintain production equipment, many things must happen. The first is to ensure the equipment is operating in the cleanest possible environment for that area of the plant. Many of the problems in industry can be corrected by following that old proverb about cleanliness. The appearance of area around most of the production equipment is a good indicator the company's maintenance policy. It also generally is a good indication of the overall condition of the equipment itself. This is especially true of hydraulic equipment.

Dirt, oil, and trash around production equipment hides many problems besides being a safety hazard. Because of its importance, safety in the work area presents a set of problems that must not be overlooked. Not only are footings unsure and handholds a problem, but leaks and failing parts are hidden. Moving or lifting equipment is hazardous. An unpleasant job becomes even more so when the working environment is unpleasant or unsafe.

A fact of life is that if management does not "walk the talk" and demonstrate concern for the equipment, then there is no reason or incentive for line or maintenance staff to have any greater concern for the equipment. In this situation, getting the job done as quickly as possible is the <I>most important<I> thing on their mind. This means doing only what is necessary, and not worrying about what actually might be required. Mostly, it indicates an employee mind set of "I can get by with this because they don't really care".  When management disregards the needs of people and equipment in favor of a short-term bottom line performance, they are forgetting one very important thing. Equipment that operates correctly is an asset that makes money for the company and should be protected as any other asset is protected.

When dirt gets into the equipment, especially hydraulic equipment, it causes erratic operation that leads to accelerated wear and early system failures. To correct this situation, the equipment and its surroundings must be clean, including the hydraulic system.

Get on with the work

Taking time for housecleaning offers an opportunity to make a complete inspection of the system. Take oil samples and send part out for analysis. These oil samples should include a simple, quick "patch test" and a more complete lab analysis. A patch test considers only oil color and the presence of particles visible with a low power microscope or hand-held magnifying glass. The patch test gives an indication of the general condition of the oil. An interpretation of the color and the nature of the foreign material might indicate pending component failure. A chart is available to aid in this interpretation.

Do not overlook the importance of an oil analysis as a regular part of every maintenance program and the direction the results lead. A complete oil analysis confirms information already found in addition to providing other data needed to establish the total condition of the oil and machinery.

Drain the hydraulic system reservoirs and spend <I>as much time as necessary<I> to make sure they are completely clean. Be sure to clean the connecting hoses, fittings, valves, and other components. Make sure the inside of the reservoir is wiped clean with lint free rags or an equivalent. Replace internal oil filter elements. Inspect the internal baffles and repair as necessary. Inspect, clean, repair or replace everything inside the tank before reinstalling the tank lids. By the way, also clean the sealing surfaces and replace the seals or gaskets around the lids. Avoid reintroducing new dirt into the reservoir before closing it up.

Drain and clean connecting equipment, hoses, lines, fittings, and so forth. I mention this twice because of it's importance. Look at anything inside the reservoir or passing through the reservoir's walls in terms of replacing closing the lid. Make sure the adjacent work area is clean. A coat of paint at this time really gives any maintenance job a "finished" look.

After cleaning the area and equipment, put the equipment back into full service as a check for system leaks and other problems that were covered by dirt. Look for such things as broken fittings, loose connections, blocked air passages in motors and heat exchangers, broken gages, and other details. In addition, this inspection gives the chance to look for other internal and external problems.

Make a written record of everything seen including the location of leaks, a listing of damaged or broken parts, and the general operating condition of the equipment. Don't forget to check the condition and settings of the pressure and temperature gauges. These are important as they help with troubleshooting to insure the hydraulic system is operating correctly. Note anything unusual. Listen for any strange noises and locate their source.

Maintenance plan

After recording the condition of the equipment and identifying and noting leaks and other problems, lay out a maintenance plan. In addition to a work schedule, this plan should include manpower, parts, and outside help required.

A typical maintenance plan includes the following items. First, clean the area then test the equipment for leaks. Look for damaged or broken parts, listen for strange or unusual noises, and, in general, see if the equipment is operating at its design specifications. The equipment manufacturer can supply operating and maintenance manuals concerning the equipment. Study the oil samples taken earlier and decide what, if any, components require repair or replacing. The maintenance plan also includes parts, labor (both in-house and contracted) and a schedule.

Check the heat exchangers. If they are air-cooled type, clean and inspect them for damaged fins and tubes. Also, look for obstructions in the air flow paths. Check heat exchangers for leaks after they have been cleaned and pressurized. Check for blockages and damaged fittings that might restrict hydraulic or cooling air flow. If possible, check the internal flow paths for blockage or restrictions. A water cooled heat exchanger might have to be sent out for cleaning, however it can be pressure- and flow-tested in house.

Next check the condition and alignment of the motor, pump, and couplings. This includes carefully looking at the pump, motor, and coupling assemblies for obvious problems. Make several quick electrical and alignment checks. Check coupling condition and alignment per manufacturer's recommendations while remembering that some couplings require grease. Check the holddown bolts and the feet of both the motor and the pump to make sure they are in good condition and free of cracks. Make sure the holddown bolts are in place and correctly torqued. Check the cooling fan assemblies in both motors and heat exchangers for cleanliness and general operating condition. Check pump for leaks, broken or damaged fittings, and anything else that affects operation. Frequently pumps and hydraulic motors can be rebuilt in place. Also, many of the seals can be replaced without removing the unit from its mountings.

When checking the condition of the hoses, look for cracking or signs of aging. This is an indication that the hose has been in service too long or the area near the hose is too hot. If the operating temperature or the environment is too high, then consider an upgraded class of hose.

Check the hose fittings for damage and leaks. In the case of metal tubing, look for crimping or other mechanical damage. Hoses and fittings frequently do more than they are designed to do--don't hang things on them or use them as handholds and steps.

For both hoses and tubing, make sure that they have enough clearance to prevent chafing on other parts. Also, make sure that the tubing and hose runs follow standard installation practices. Hoses tend to be left in service longer than they should be and they become brittle. This leads to leaks and catastrophic failures. After repairing or replacing the damaged hoses, tubing, and fittings, see if they can be protected by rerouting them or moving them out of the way.

Check control valves for leaks at sealing joints or surfaces including subplates or end caps where control shafts come through valve bodies. They should be checked for their general operating condition. Many valves can be rebuilt in place as easily as replacing them. This is generally true of larger valves, saving both time and money.

Many things cause control valve failure. The first is usually dirty oil and equipment cleanliness. Dirty oil is also the most common cause of valve failure. After disassembling the valve, clean and inspect it. Inspect and replace wear parts, if necessary. Always replace seals or gaskets. The manufacturer can provide the necessary dimensions and part numbers. These wear parts include springs, seals, and those parts recommended by the manufacturer.

When reassembling, make sure the work area is clean. It is also critical that the components themselves be clean. Do not reintroduce dirt into the valves as doing so causes erratic operation and reduced valve life. Follow the manufacture's instructions for the sequence of assembly.

Check the condition of actuators, accumulators, and other hydraulic components used in the system. Look for leaks, broken or damaged fittings, damaged body parts, misalignment and chaffing. Leaks usually occur at the shaft seals and sealing surfaces. Many of the seal leaks are caused by dried out seals or seals damaged by a dirty working environment. Again, dirty oil abrades shaft seal and shaft surfaces.

Over time, even with wiper rings in a shaft seal assembly, expect to bring some dirt back into a hydraulic system that will get into the seals to cause shaft damage. Dried-out seals also cause damage to the sealing surfaces that they move against. A major causes of shaft seal leaks are the dirty environment (both dirty oil and dirt on the piston rod) and misalignment of the actuator. Many fitting leaks occur because clearance problems allow them to hit or rub against something. As you probably know, many actuators can be rebuilt in place.

After the system has been cleaned and repaired, consider filtering the oil. Use a correctly sized filtration system with a capacity consistent with the system that has just been cleaned. Monitoring the system insures that the oil remains clean.

Before the system is placed back into full service, run it under pressure to insure the oil and internal portions of the system have been flushed properly. This allows cleaning the entire hydraulic system. Take new oil test samples and confirm the condition of the filtered oil. Taking proper care of oil keeps it remaining clean. Remember, it is cheaper to keep the oil clean than it is to change it, clean the system, and dispose of the oil through the plant's waste stream. It is cheaper to keep the oil clean than it is to pay the price for downtime, lost production, and vanished profit. It pays to keep your assets functioning.

The big picture

What should be obvious is that many problems and much expense can be saved without using outside consultants. You have what is already needed in-house. Maintaining a clean environment does require a serious effort, but the payback is worth it. Develop a maintenance program that is continuous and is followed.

In the final analysis, maintenance is not an overhead expense, it is the cost of doing business. It falls into the same category as a utility such as gas and electricity. Remember, your equipment is an asset and must be protected to keep it making money for you. If you cannot find a way to take care of it in-house, then contact a consultant. Either way, you will continue to make money.

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