Preventative maintenance is achieved through good design, procedures and record keeping.
Each piece of hydraulic equipment should be considered for its own operating conditions and environment to establish whether its duty can be improved and service life extended.
Design features and recommendations for improving service life are covered in the previous training module.
All maintenance procedures should be written down and approved by others. They should include requirements for:
The delivery and storage of fluid and components in a clean, temperature and humidity controlled environment. Clean areas for the assembly or repair of hydraulic equipment that are separate from any drilling, grinding or welding areas.
All maintenance and repair work should be recorded in a system that is readily available to everyone else involved with the equipment. This will act as a way of measuring and justifying the need for any design changes that will help reduce downtime or failures.
Always isolate the supply and fully vent the system pressure before starting any maintenance. Maintenance engineers shall be fully familiar with their duties as employees under HSAWA Act 1974.. They must also be aware of the basic dangers and Potential Risk from Fluid Power that has already been covered in the earlier sections.
Before any maintenance work is started the responsible engineer must prepare a full list of the things they need. These are likely to include:
Read all relevant specifications and standards.
Obtain copies of circuit, parts list, assembly drawings and datasheets etc.
Arrange all necessary tools and special equipment.
Order parts and materials.
Complete risk assessment and safety precautions including PPE.
Check for environmental risks or hazards.
Because the design, duty and environment of every hydraulic system are different, the maintenance planned for each system will also be different and must, therefore, be worked out against its individual requirements. This section can only provide a guide to what should be considered but will not, therefore, be an exhaustive list or one that can be applied to any specific machine.
Systems may be designed to last:
250 hours (garden tractors, tail lifts etc.)
1000 hours (implements on backhoe loader, low cost industrial etc.)
10000 hours continuous operation (Heavy industrial etc.)
These figures are based on full load operating hours and should be longer if the duty is only light.
The equipment manufacturer may be able to advise pump and motor replacement times although this is likely to depend on how clean the fluid is maintained. Monitor case drain or casing temperatures and system flows or cycle times for an early warning of when pumps might fail. Always try to change a pump early, before it fails, as a catastrophic failure we create massive levels of contamination that will pass around the circuit and probably require the whole system to be rebuilt.
Filters and air breathers are probably the most important components in every system. Always monitor their clogging indicators and change when required. The frequency of replacement may be linked to the type of work they do so it's recommended to check the fluid condition regularly.
Never forget your air breather! This is vital for keeping airborne dust out of the fluid. Too many low-cost power units only have filler cap with a strainer and we'd always recommend you replace this with a proper filter element. And replace them as required.
Hydraulic fluid is as important to a hydraulic system as blood is to our bodies. Analysing the fluid also provides a very good guide to the health of our equipment. As well as the contamination level, a particle analysis will show what materials are present and therefore indicate where the dirt is coming from or which components are failing. Fluid properties will also show if it has been overheated or exposed to such high-stress loadings that the viscosity or other properties have been damaged.
Most cylinders should be capable of completing 1 Million cycles before the seals need to be replaced. This will, however, be very much dependent on the environment, in particular, how much dirt gets on the cylinder rods, if rods are stored in the extended or retracted position, and what level of side loading or shock they are exposed to.
For more information see hydraulic cylinder tips for operating and maintaining
In theory, a spool valve should never wear out as the spool body should never come into contact with the bore. In practice, the lower cost valves may not be made perfectly round and concentric and every particle of dirt that passes through the clearance will apply some side load. The more dirt that enters a valve, the more dirt gets created by the spool element rubbing on the bore. These contact points can be clearly seen on the sides of a spool and are a strong indication of which valves might have been causing any intermittent operational issues.
For more information see directional valve tips for operating and maintaining
Poppet valves rely on a perfect fit of the poppet nose into the valve seat. Eccentricities or damage to the sealing between the nose and the seat will lead to increased leakage, which may mean the valve needs to be replaced. This type of damage is typically caused by contamination and will probably leave signs of damage on the poppet's spool body.
Repeated or harsh operation where the poppet nose bangs against the seat can lead to distortions in the nose and seat. This damage can lead to changes in the performance of the valve or increased leakage.
It is important to track all downtime, faults and failures in your maintenance record.
Keep a detailed record of all work that has been carried out on the system.
Note the type and cause of any failures preferably using appropriate maintenance management software.
Good record keeping will allow you to measure, benchmark and track the success of your maintenance programs by comparing the results year on year.
Records may include areas such as motor current draw, reservoir temperatures, flows (sequence timings) and pressures, contamination levels, filter clogging switching, system temperatures, pump case drain temperatures and flows, servo and proportional valve signals/feedback, hose replacement dates, check for visible leaks, damage or debris around system. Listen for unusual or higher than normal sounds. Take vibration reading for the motor.
Maintenance records can provide a vital source of information when breakdowns occur. Always refer to maintenance records for potential solutions. All events should be recorded as they may contain valuable leads to the fault, such as other components having recently been changed.
We have not included any specific fault finding recommendation in this section because the approach will differ for each application.
Completing the whole e4training.com course will provide you with an in-depth knowledge of hydraulic equipment and is the best preparation for making informed, fault finding decisions.
It is important to always follow the written procedures from your employer and/or equipment manufacturer.
Prior to any work commencing, the responsible authority must ensure that all personnel have completed the proper training, specific to that equipment.
Written procedures are likely to include:
Equipment shutdown routine.
Correct PPE to be worn.
Isolation, lockout and tagging requirements.
Correct tools required including any specialist equipment.
Proper diagnostics and measurement tools.
The correct procedure for reporting any incidents whether an injury has occurred or not.
Confirmation and location of completed risk assessment.
See more information on safe start up and shut down procedure in our fluid risk section.