Dirt ingression when adding fluid is one of the most common problems. If containers are used to transfer fluids, they should be clean and resealable so you can close them up immediately. “But most importantly, the fluid you are adding to the system should be pre--filtered,” says Kanitz. Bulk oil tanks should be equipped with filters. “That is probably the most common mistake because new oil is not necessarily clean oil.”
Nicol adds, “Operating a system with a low fluid level increases the chances for entraining more air in the fluid. Aerated fluid will damage the transmission and it will accelerate the oxidation of the fluid.”
Hydraulic circuit maintenance includes making sure the oil filters are changed according to service guidelines; hoses are in good condition; oil coolers are working properly; and any venting device is operating correctly, according to Sporrer.
Finally, service procedures require strict adherence to published guidelines. For example, know the torque on fittings and do not over torque these items, Sporrer advises.
Technicians also need to be careful they do not damage sensitive electronics on today’s sophisticated hydraulic systems when servicing the transmission. Sporrer notes that many failures can be traced to wiring damage. “As they are servicing a product, they damage the sheaving on the wire,” he points out.
Maintaining cleanliness when servicing the transmission is a must. “Many hydraulics shops have a clean room where they do all of the assembly and disassembly of hydraulic components,” says Nicol. “This protects internal parts from exposure to contaminants that are normally present in the shop.”
Make sure the entire area of a machine is clean prior to removing any part of the system. Any opening should be sealed to keep contaminants out. This includes all hydraulic hoses and tube assemblies. “All fluid conveyance lines affected by failed hydraulic components or new replacement lines should be properly flushed and visually inspected to make sure there isn’t rubber dust, steel braid or other contaminants present prior to installation,” says Kanitz. “During installation, have the hose assemblies and components capped. Do not remove the caps until you are ready to install the fittings and complete the plumbing.”
Any dust or debris which enters the system will eventually result in another failure. If possible, perform all repairs in a dust--free environment.
Measure Hydrostatic Transmission Health
One gauge of hydrostatic transmission health is the charge pressure. “In our service literature, we include a step--by--step procedure for checking the charge pressure at low idle, at high idle and with some load,” says Sporrer. “Different manufacturers prefer different settings. They range from 200 to 500 psi.”
Low pressure indicates a potential problem. “If one of the components begins to wear out and the system is leaking more than the charge pump can make up, replenishing (boost) pressure will begin to drop,” says Nicol. “Catching this early can prevent a catastrophic failure that would be more expensive and time consuming than fixing the worn--out component.”
Oil analysis also plays a key role in monitoring transmission health. It provides a picture of what types of contaminants are in the oil and in what quantities. “[Oil analysis providers] will give you a judgment on whether or not you need to service the machine right now or whether the contaminant level is normal,” says Sporrer. This can head off larger problems.
“Eaton can provide a complete report that not only indicates the fluid cleanliness, but it will show the condition of the system itself and if there is a component that might be nearing failure,” says Kanitz. “In many piston pumps there is a bronze material that contains copper. If there are a lot of copper particles in the fluid, we can tell that there might be evidence of either cavitation--type damage or contamination--related damage.”
You can also gauge health through the actual performance. “If the system’s performance starts to degrade, it could be due to a number of different factors,” says Kanitz. “It could be due to the filtration going into bypass and the filter being plugged up. Most hydrostatic transmissions, if they are designed correctly, will become sluggish when the charge filtration starts to plug.” Also check to make sure case drain lines are not pinched or restricted as this can cause system overheating.