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There is no replacement for good understanding and experience of hydraulic equipment or a logical approach to problem-solving. However, following this structured procedure as well as using the troubleshooting app to provide suggestions for some common causes, may help. The following paragraphs provide a troubleshooting procedure checklist that should be used in conjunction with the troubleshooting 'likely causes' database.
Obtain all circuit drawings, documentation, datasheets and maintenance records. Compare part list numbers with those shown on the valve nameplates to see if they have been changed.
Speak with operators and maintenance staff to establish all recent and past historical breakdowns and upgrades etc. Pay attention to their eyes when you ask them about the possibility that the equipment may have been run outside of it's recommended operating window. It's unlikely they will admit for potential miss-use.
Check when pumps, valves and filter elements, particularly suction filters, were last replaced. Compare this will calculated or expected pump and filter life.
Complete a risk assessment and ensure all relevant training has been completed.
Review the startup and shut down procedures and any specific safety risks.
Check all basic readings and resources e.g. fluid cleanliness, reservoir fluid volume, ambient temperatures, filter clogging indicators, air breather condition, water supply, electrical power and stability. Look for any fluid leaks or wear and damage on actuators or other equipment.
Check all isolators are open and that no one has started work or repairs on any other part of the system.
Feel the pipework as the equipment starts to warm up. A valve that heats up quickly will be passing flow across it with a high-pressure drop. Pilot drain or return lines temperature changes will highlight any leakage or losses. Compare reservoir heating times with simulations in our design guide calculations to identify potential variations from those expected.
Compare new system performance measurements with normal operating conditions. Document as many readings from existing test points and instrumentation as possible. Make sure all of the instrumentation has a valid calibration certificate.
Keep a detailed record of each step or test you make. It's very easy to forget what changes have been made or how they affected the performance. It is also likely you will need to present and review your work with others later and a good list is vital for focusing ideas in the right direction.
Begin by focusing on any unusual noises, sequencing, or responses, although if you are reading this I guess we can assume there is no obvious solution.
Measure the performance under different operating conditions to check whether the equipment behaves as expected. For example, running at low, medium, and high temperatures may point to certain control issues while operating with low, medium, and high loads may indicate others.
Operate actuators individually and at the same time. Comparing the performance results may show speed or pressure differences that can point to potential causes. Pay careful attention to pilot flows as small changes in pilot line flows or pressures can have a large effect on the main valve's operation. If you don't have separate pilot drain lines then pay even more attention to valve pilots. Sudden changes in return line pressure will be felt by every pilot valve and will then be passed onto the main valve section as well.
If possible and safe, try to isolate and operate only the particular part of the circuit where the problem is, this should remove any external influences.
If safe, operate the directional valves manually to check they are working or use a separate electrical switch box for testing, if available. Try manual switching with no pressure to check if the spools move freely or are locked or sticking.
If safe, adjust the supply or control pressures to ensure they make the changes expected. In general, the performance should only be controlled by one component so if this component does not have full control then it's likely there are restrictions somewhere else. Remember, hydraulics is a braking technology so look for the single main restriction that is being used to brake and control the load.
Use a pressure transducer with a fast sampling rate to record a clear graphical output of the pressure signal. This will show dynamic pressure changes that are no visible on a traditional bourdon tube pressure gauge.
Compare pressure rise rates during switching with the limits specified on the pump manufacturer data sheets. Peak pressure overshoots may also exceed acceptable limits.
Valve switching rates are often controlled using small internal orifices. Designers don't generally have enough information to specify these accurately before commissioning so they may need to be changed for different environments or they may indicate other factors that have changed.
Bang the end of each actuator with an appropriate load and measure the frequency response signal shown by the transducer. This will demonstrate the system natural frequency which can be used to calculate the maximum response rate that can be expected and therefore the appropriate control signals. They may be different from the theoretical ones calculated during the design process.
Data-loggers record significant amounts of data for extended periods of time. This may be the only way to identify enough information about the sequence of events that finally point to the original cause for the issue. Consider what valves should be switching at each point and what would happen if they didn't. Review where high-pressure drops exist across spool lands. These are the areas where contaminants are likely to gather and the valves that unlikely to move, every time they are asked to.
Overall troubleshooting is a matter of looking for clues and working out what might be their cause. More often than not the reason for the issue is not in the same place you see the fault. Sometimes you just need to change something that looks completely unrelated only to discover that it identifies the clues that allow you to discover the cause.
There is no way to quickly troubleshoot problems without experience but no way to gain great experience without troubleshooting problems. Work hard and methodically, study the detail, follow a logical procedure, get lucky, and enjoy. Hydraulics is certainly one of the most interesting engineering disciplines and you never stop learning.
Skill Level 1 Standard Machine. An OEM Production machine where the design has been proven to work well under all operating conditions.
Skill Level 2 Repaired Machine. A recently repaired or newly commissioned machine with potential setup issues.
Skill Level 3 Unproven Design. A specialist, custom or new design of machine, or one that is being used in under new environmental conditions.
See all of the potential issues associated with this diagram.
Safety and Environmental risks
Risks to health or the environment for which safety precautions are required or the operators require safety awareness training.
Contamination / Reliability
With over 80% of failures caused by contaminants in the fluid, this section highlights the most common areas where dirt can enter the system, or be generated inside the hydraulic system. It also highlights common faults with sensitive components.
Noise (Low or high-frequency sound, not load judder)
Unusual noises are sometimes the first sign of a problem. Measuring the frequency of the noise is a good way to establish the causes although often measuring the accompanying flow effect or pressure signal will provide more useful information for diagnosing the cause. A low-cost mobile phone spectrum analyser app can help find the key frequencies.
Temperature (Ambient temperatures and heat generation)
Increased or reduced temperatures are often a good way of predicting where faults occur. The reservoir temperature is always critical but measuring pipe temperatures after relief valves, for example, can show if the valve is open or leaking. Keep a record of normal operating temperatures so that you can compare these with new readings later.
Speed (Flow rates and actuator movement)
Timing the speed at which actuators move or sequences switch can give a clear indication that something is wrong. It is helpful to be able to compare faulty actuator timings against a record of original equipment speeds.
Force (Pressure and load affect changes)
If actuators are unable to move the load or respond too harshly then the operating forces are probably not balanced correctly. System load regularly change during operation and often cause complex shock or standby conditions. Pressures can read lower than normal if force issues arise.
Sequence (switching and timing order)
Sequence faults might include equipment operating sequence or timings not performing correctly. This may include an electrical signal, limit switch or pressure sequencing device errors.
Judder/erratic operation (low or high-frequency oscillations of the load)
Harsh cylinder banging, pipes or loads shaking are all indications of hydraulic judder.
Control (when loads are regulated and not just open or shut.)
Servo and proportional systems may suffer from control errors such as positional or force accuracy, hysteresis, speed, or response times etc.
Intermittent (Faults that only occur now and again)
Many faults arise from unexpected or extreme operating conditions that have not been properly protected against. For example, trapped in pressure, shock loads on a cylinder or high and low temperatures are not unusual but are often not fully protected against by the original design. These also include standby or extreme limits, intermittent or exceptional load conditions and undemanded movement.
Efficiency (identifying areas where the energy used can be reduced)
The present climate emergency means it's vital we make every effort to reduce energy consumptions and therefore the burning of fossil fuels. This section will help you identify areas where this may be possible.