Part 1 of a 3 Part Series
The components of hydraulic systems work together intimately. As a result, damage to one component may cause further damage to others. For instance, overheated oil caused by a leaky cylinder seal can break down and cause damage to other cylinders or the pump. That’s why it pays to perform regular maintenance and preventative inspections to eliminate problems before they occur.
Most hydraulic systems consist of a pump, hoses and lines, cylinders and motors, valves, a cooling unit, a reservoir, filters and hydraulic fluid (oil). At the heart of the system is the pump. It uses energy from the engine to pump the fluid and create hydraulic flow and pressure. Valves control the flow of the fluid by restricting or redirecting it. Cylinders and motors are the “muscles”of hydraulic systems. Cylinders have a straight, push-pull action while motors use the energy from the fluid to turn a shaft. The speed at which these components operate is determined by the hydraulic-oil flow rate, while the hydraulic pressure determines the force they exert. The cooling unit acts to cool the fluid after it has gone through the system and the reservoir feeds the pump.
The basic prescription for hydraulic maintenance is prevention. If you keep contaminants out of hydraulic systems, you will avoid nearly all common problems and failures. However, some contaminants inevitably do enter the system and scratch close-fitting surfaces in the components. Therefore, follow these guidelines to keep your hydraulic fluid in top condition.
- Keep contaminants out of your hydraulic system. Clean the area around dipsticks, fill plugs and hydraulic filters before removing them to check or change the hydraulic fluid. Keep all fluid containers tightly sealed when stored and pour directly from the container into the system.
- Change the fluid and filter after the initial 50 hours of use. Often, the manufacturing process allows contaminants to enter the hydraulic system. A fluid change after 50 hours will eliminate these particles. Thereafter, change hydraulic fluid and filters at regular intervals.
- Check oil before each use. Verify that fluid levels are adequate and that the fluid is in good condition. An inadequate amount of oil can cause severe damage to pumps. If your oil appears foamy or milky, you may have a leak that is causing air to enter the system. Air will cause jerky and slow operation of the hydraulics. Locate and seal the source of any leak.
Also, air within the system holds moisture. When the system cools down after operation, the moisture can condense and mix with the hydraulic fluid. Water in the hydraulic fluid looks similar to the milky appearance resulting from air contamination.
Regularly check the temperature of the hydraulic fluid during operation. Is the fluid too hot to touch? Does it smell burnt? Your cooling system may be not working properly or you may have pressure-related problems. Check the hydraulic oil cooler or reservoir. They must be kept clean. Remove any dirt or other debris that inhibits airflow around them. If the fluid remains hot for extended periods, it can break down and lose its ability to lubricate adequately.
Hydraulic System Care – A 10-Point Weekly Checklist
Hydraulic system maintenance is a critical component to ensure your machinery stays in top working order. Basic system maintenance can help you avoid an untimely and expensive breakdown. Here’s a quick basic checklist that you should be familiar with.
10 Point Check: Any operator responsible for hydraulic system maintenance should, at minimum, perform the following 10 point checklist as part of a weekly “quick scan” of every hydraulic system.
- Check fluid levels. Add hydraulic fluid as needed (if needed). Not all hydraulic fluids are the same, DO NOT MIX OILS! Use the same oil brand and viscosity grade that is specified.
- Inspect breather caps, breather filters, and fill screens — DO NOT punch holes in screens in order to expedite adding oil as this may allow contaminants into your system.
- Check filter indicators and/or pressure differential gauges. Immediately replace any that show signs of wear or other negative indications.
- Visually inspect all system hoses, pipes, pipe connections for leaks, frays, bubbling, or chaffing spots. Hydraulic ﬂuid leakage is a common problem for industrial systems. Excessive leakage is an environmental and safety hazard, increases waste streams and oil consumption, and, if ignored, can reduce the system capacity enough to overheat and slow normal system operation. Further, leakage is often an indication of seal wear or other compromise associated with impending failure.
- Check system temperature via built-in thermometers or hand-held infrared detectors. Normal temperature range for most systems is 110-140ºF but may vary. If temperatures are high, check fluid quantity, cooler operation, and relief valve settings.
- Visually inspect the inside of the reservoir for signs of aeration (via the fill hole using a flashlight). Aeration is a condition in which discrete bubbles of air are carried along in the stream of oil as it enters the pump. Visual signs of aeration in the reservoir are generally foaming and/or little whirlpools taking small gulps of air into the suction strainer. Causes of aeration include: low fluid levels; air leaks in the suction line, low fluid temperature, fluid too viscous to release air or maintain suction at the pump, or faulty shaft seals. When air leaks are suspected on the suction line, smothering these points with oil will usually pinpoint the leaks by creating a marked change in pump noise. A pump ingesting air sounds as if it were gargling marbles.
- Listen to pumps for the signs of cavitation. Cavitation is slightly more complicated than aeration, but has some similarities. Cavitation occurs when air is released from the hydraulic oil during momentary depressurization at the pump suction and then implodes onto metal surfaces upon discharge. These implosions are extremely destructive to pump surfaces. A cavitating pump will emit a high-pitched whine or scream. Causes of cavitation are the same as those of aeration with the exception of suction side air leaks. How do you discern aeration from cavitation? One way is to install a vacuum gauge on the suction side and make sure the pressure is equal to or greater than that prescribed by the pump manufacturer. Foaming in the reservoir is usually the telltale sign of aeration.
- Inspect a small sample of ﬂuid for color, debris, and odor. Keep in mind that visual inspection is limited in that it will only detect signs of excess contamination.
- Scan electrically controlled servo valves with an infrared thermometer. High valve and solenoid temperatures (over 150ºF) usually indicate the valve is sticking or bypassing. Sluggish operation and violent system “jerking” around valves is a sign of possible contamination.
- Scan the electric drive motor for housing hot spots and rotor bearing temperatures using an infrared thermometer. Any such finds and the system should be immediately tagged out and serviced.
These basic tips will help keep your hydraulic system in top operational shape and reduce chances of untimely and expensive breakdowns.