1. Fluid Power System Maintenance and Troubleshooting
Chapter 14
Fluid Power System Maintenance and Troubleshooting
Fluid Power System Maintenance • Fluid Power System Troubleshooting

2. Hydraulic system maintenance is performed based on the results of routine inspections of equipment and systems within a specified period of time.
The advantage of a routine maintenance program is that it reduces the amount of troubleshooting that may need to be performed. Many future problems can be avoided. Separate maintenance programs are applied for hydraulic and pneumatic systems. within a specific period of time. The frequency of inspection varies with the manufacturer’s recommendations. If those are not available, mobile hydraulic equipment typically should be inspected every 400 hr to 600 hr, or every three months. Industrial hydraulic equipment should also be inspected every three months if the manufacturer’s recommendations are not available. Inspection intervals are based on conditions that include operating temperature, pressure, accessibility, operating time, and environmental factors such as shock, vibration, operating time, and cleanliness. See Figure 14-1.

3. Mating surfaces in a hydraulic system can often have maintenance problems due to contamination and breakdown of the hydraulic fluid.
Most hydraulic system maintenance problems are caused by the contamination and breakdown of hydraulic fluid. Air, water, dirt particles, and other contaminants can accumulate in hydraulic fluid to create sludge and corrosive acids. Contaminants can clog small openings and cause severe operating problems. Acids corrode metal components, plastic seals, and hoses. Contaminated hydraulic fluid also has diminished lubricating capabilities. This can cause a component with mating surfaces, such as a cam ring in a vane pump, to rapidly wear. See Figure 14-2.

4. Hydraulic cylinders that are not in service must have their rods retracted to prevent contaminants from settling on any exposed metal and entering the system when the rod is moved.
Hydraulic cylinders that are not in service must have their rods retracted to prevent contaminants from settling on any exposed metal and entering the system when the rod is moved. See Figure Rods that must be stored exposed should be coated with grease that can be easily removed before startup.

5. Fluid stains or puddles under hydraulic equipment and hoses indicate the presence of a leak in the line.
Hoses should be regularly inspected for signs of wear, cracking, abrasion, fluid seepage, blisters in the outer covering, deterioration, uneven twists in the hose line, coupling corrosion, or hydraulic fluid leaks. Hoses with any of these types of problems need to be replaced immediately. Fluid stains or puddles under hydraulic equipment and hoses indicate the presence of a leak in the line. See Figure 14-4.

6. Hydraulic hoses must be properly installed for maximum operating life.
Hydraulic hoses can be damaged if improperly sized, constructed, or installed. Elbows and adapters are used to relieve strain on hoses. Hoses should not be allowed to rub against anything that could remove their outer layer. They should be properly installed for maximum operating life. See Figure Clamps are often needed to support long hose lengths or to keep the hose away from moving parts.

7. When preparing metal surfaces for use in fluid power systems, they should be polished with soft, nonabrasive, manufacturer-approved cleaning pads.
Metal surfaces can be damaged due to excessive force. When preparing metal surfaces for use in fluid power systems, they should be polished with soft, nonabrasive, manufacturer-approved cleaning pads. Abrasive grit can remove surface metal and cause internal leakage. Only approved cleaning products and materials supplied or recommended by the manufacturer should be used. See Figure 14-6.

8. Pneumatic system maintenance requires regular inspection and replacement of compressed air filters.
The lubrication, cooling, and filtration systems of large air compressors, such as those used in industrial facilities, must be monitored carefully. The correct type and amount of compressor oil is critical to proper air compressor operation. The alignment of the prime mover and the air compressor must regularly be inspected. Compressed air filters must be inspected and replaced on a regular schedule. See Figure If a belt-driven air compressor system is used, the condition of the belt must be inspected. Equipment maintenance requirements are compiled and scheduled into the overall pneumatic system maintenance procedures.

9. A hydraulic tester is used to measure the pressure, flow rate, and temperature of hydraulic fluid in a system.
Internal leaks from hydraulic components, such as pumps, relief valves, and directional control valves, can be isolated using hydraulic testers. A hydraulic tester is a device that measures the pressure, flow rate, and temperature of hydraulic fluid in a system. Flow rate and system pressure are tested at various points in the hydraulic system. See Figure 14-8.

10. Troubleshooting procedures are followed and documented to isolate and correct hydraulic system problems.
Hydraulic systems that are critical to production must operate without interruption, and their downtime must be kept to a minimum. Troubleshooting procedures are followed to isolate and repair problems as quickly as possible. Troubleshooting procedures and results should always be documented for future reference. See Figure 14-9.

11. The most common problem in pneumatic systems is insufficient airflow caused by leaks from worn, disconnected, or kinked hoses or tubing.
Depending on the manufacturer, some pneumatic hoses have reinforcement layers rather than cords. In these hoses, the inner reinforcement layers can collapse and are not seen on the surface. Many modern pneumatic systems use clear or semiclear polyurethane (plastic) tubing without reinforcement layers or cords. Damaged inner linings are visible in these types of plastic tubing. Hoses and tubing can also become kinked, blocking airflow. See Figure

12. Air leaks can waste up to 25% of a pneumatic system’s energy.
Air leaks in a pneumatic system are costly and must be repaired quickly. In many applications, air leakage can waste up to 25% or higher of the pneumatic system energy. See Figure Air leaks can be located by listening for the noise of discharging air when the work area is quiet or by applying soapy water to the suspected location of the air leak. The soapy water will produce bubbles when applied to an air leak.

13. Plug-in pressure gauges can be used to trace pressure levels through a pneumatic system.
Actuator packing nuts should not be overtightened. A packing nut is a mechanical device on a pneumatic actuator that applies tension to the seals or packing to prevent air leaks around the circumference of a rod or shaft. Depending on the application, plug-in pressure gauges can be used to trace pressure levels through a pneumatic system. A plug-in pressure gauge is a pneumatic device that can be added to or removed from a pressurized pneumatic system without removing pressure from the system. For example, plug-in pressure gauges are typically used to verify that the pressure in a pneumatic hand tool is at the proper level. See Figure

14. An itemized equipment operation checklist can help an equipment operator provide information that can reduce the amount of time needed for the troubleshooting process.
Typically, the best source for specific equipment information is the equipment operator. This can help reduce the amount of time required for the troubleshooting. See Figure

15. Troubleshooting electrical problems with an electrically controlled hydraulic system is performed by taking voltage or continuity readings.
If the switch is open, the voltage measurement should be the same as the source voltage. If the switch is closed, the voltage should read close to 0 V. If neither of the measurements is indicated by the DMM, the switch could be faulty. See Figure