One of the most vital systems that you need to consider in extending the life of a machine is your hydraulic system.
An asset manager’s goal is to maximize the value of equipment over time. In most cases, this means a machine has to be in good working order and making money for you long after it’s paid off and long after the warranty period has expired. This is the time in the asset’s life that it provides the most return to your business, provided that you can keep it performing at a high level. Keen attention to the maintenance of your machines maximizes their value in the event you decide to sell or trade up. Ensuring that your machine operates into this “golden period” depends upon strict adherence to a routine preventative maintenance schedule that begins before a wrench is ever picked up.
The Real Cost of Hydraulic Leaks
According to a study published by Mobil Oil’s commercial marketing department, one leak at a rate of a drop every five seconds amounts to 80 gallons of hydraulic fluid per year. That $400 may not seem significant, compared to the cost to repair, but once you factor in the estimated $7.00 that will need to be spent on cleanup per every dollar spent on the lost oil, you can add another $2,800 to the financial impact, for a total of $3,200 for one drop, every five seconds, from one leak point. How many leaks will you tolerate with this in mind?
Here are some other costs to consider:
- Cost of personnel and their expenses during cleanup
- Cost of clean-up contractors if necessary
- Regulatory fines/penalties due to the spill
- Cost of oil lost
- Cost of damaged equipment, infrastructure
- Natural resource damages (if applicable)
- Cost of spill control supplies, equipment
- Cost of claims by third parties
- Loss in productivity
- Increased attention from regulators
- Need for more training, inspections, planning
- Damage to business reputation
- Higher insurance premiums
- Increased space required to store spill control supplies
One of the most vital systems that you need to consider in extending the life of a machine is your hydraulic system. In creating a maintenance plan for your fleet’s hydraulic systems, the manufacturer’s suggested service intervals are just one input that you should consider. Your OEM doesn’t consider the variables of operator skill, climate, environment or a host of other conditions in the development of their preventative maintenance (PM) guidelines. A successful PM program relies on monitoring a variety of inputs, including those of the operator, to establish a schedule that best meets the requirements of the conditions in which the equipment operates. In order to prevent failure and still obtain the maximum value from your asset, your PM should be routine and as unobtrusive as possible to the productivity of the machine.
Before discussing an approach to preventative maintenance (PM) programs for hydraulic systems, maybe it’s best to take a moment to talk about what types of failures can occur. In general, failures come in three forms.
Degradation failure is the type of hydraulic system failure most often associated with machine age or use. Degradation failure is the gradual deterioration in the performance of a component caused by wear or the effect of induced contamination, resulting in the need for repair or replacement.
Another type of failure is referred to as transient failure. As the name suggests, symptoms of this type of failure may come and go, although generally, the consequences are much longer lived. An example of a transient failure might be particles that momentarily interfere with the function of a component. The particles lodge in a critical clearance between matching parts, only to be washed away during the next operation cycle. Presence of transient failures are often first noticed by equipment operators (“the machine felt a little hesitant”), which underscores the importance of including their input in any hydraulic PM program. Operators should be encouraged to report immediately any aberrant machine performance to their service superintendent because these failures tend to be symptomatic of larger issues.
Failure to address transient failure issues over extended periods of time can result in catastrophic failure. This type of failure usually occurs “without warning,” though prior warnings most likely went unheeded or unreported. This type of failure is generally the most costly to repair, and costs associated with them can far exceed the time, labor and parts required.
In an ideal world, developing a PM program that addresses the causes of degradation failure would effectively mitigate the other types of failure. But this is not the reality we live in. The reality is that the equipment that you manage probably varies in age, and you may not be the first or only owner. Therefore, you don’t know how well it was maintained, or how often it was serviced. The other truth is that there are some components of a hydraulic system that just have a limited life span. These so-called “wear components” include hose assemblies, O-rings and seals. Given these factors, a well-designed PM program should align with all three potential failure types.
The first line of defense in mitigating failure of a hydraulic system is to incorporate contamination measurement and control protocols as an integral element of your PM program. This is not to suggest that your shop has to be a clean room; the goal is to recognize the sources of contamination and ways to reduce it. Contamination, as with failures, comes in many forms, the most common of which include the following:
Regardless of the source, these contaminants can rarely be seen by the naked eye. As with engine oil, the key to identifying contaminants that may be present in your system lies with routine fluid sampling and analysis.
Fluid analysis identifies contaminants at a chemical level. The presence of certain contaminants can be a predictor of the source, and therefore, they can be an indicator of an approach to resolving the issue. See the accompanying table for some common indicators. Chemical analysis of hydraulic fluid is best left to a lab, and many offer this service at a relatively low cost.
A fluid’s particle count is a clear indicator of the severity of contamination or potential to cause further damage. There are many commercially available particle counters on the market that make particulate measurement a cost-effective endeavor.
More frequent drain and change intervals is one approach to contamination reduction, but one that will probably have a negative impact on machine productivity. Close attention to the type and quality of the filters that you employ at various points in your hydraulic system is likely going to be more cost effective. Warning: all filters are not created equal. Although filters vary greatly in two important factors—the size of the particle they are intended to filter and the flow rate through which media (hydraulic fluid, in this case) passes through the filter—filters that may seem comparable can also vary in the type of media used, manufacturing process and other more subtle differences. Ensure that the filters you use meet or exceed the acceptable levels for particulate filtration and flow rate for the filter location within the system and the equipment that you are managing. Refer to OEM guidelines for specifications.
Even with a rock-solid contamination control program in place, contamination will inevitably migrate into your hydraulic system to the point where its effects become noticed by your operators or technicians. Sticking valves, machine hesitation or lag, or general sloppiness can all be symptoms of a potential problem. Since these problems can come and go, having the tools and processes in place to identify and quantify these hard-to-replicate situations is something that is best addressed by incorporating a system of diagnostic tools into your PM toolbox.
Diagnostic tools can be as simple as a plug-and-play digital pressure recorder that measures pressure spikes or drops experienced during a shift or over an extended period of time. They can be as complex as those that measure a variety of key hydraulic system data points simultaneously, including pressure, temperature, flow and rotational rate with recorded data exported into the data analysis software of your choice. This data can be compared with OEM specifications to identify potential issues or to prioritize additional maintenance tasks before they lead to catastrophic failure.
The application of any data-gathering device will require a bit of forethought, including the installation of quick-connect test points at key locations within a hydraulic system. Once installed, these test points provide easy access to the information that can be indicative of a greater problem and will dictate your approach to resolving it.
All of the detail provided by your contamination control and diagnostic processes will be extremely valuable in showing a potential buyer that you’ve taken seriously the care of your equipment and have the documentation to back it up. A folder full of documents that give evidence of everything you’ve done to keep a machine in top condition can have a substantial effect on the selling price or trade-in value of a machine that could outweigh the investment you made in its care.
The inspection of a machine’s hydraulic system as part of every operator’s daily routine ensures that any issue that needs to be addressed is caught as early as possible. Inspect every machine, every day, the same way. This inspection checklist should ideally be performed at the beginning and end of every shift, and submitted to the shop superintendent for review. Your team should determine the level of detail for these inspections, but they should be consistent from machine to machine and rigorously adhered to.
Operators should make special note of any transient failure issues they experienced during their shift, and should inspect their machine for the following early warning signs of catastrophic failure. Hydraulic systems are potentially hazardous. Service required should be performed by a technician specifically trained in hydraulic system plumbing and maintenance.
Hose assemblies. Visually inspect hoses for the following conditions, any of which indicate the need for immediate replacement: fitting slippage on hose; damaged, cracked, cut or abraded cover (any reinforcement exposed); hard, stiff, heat-cracked or charred hose; cracked, damaged or badly corroded fittings; leaks at fitting or in hose; kinked, crushed, flattened or twisted hose; and blistered, soft, degraded or loose cover.
Hard lines. Visually inspect hard lines and tubing for signs of fatigue, cracking, kinking and leaks either in the length of the tubing or at connection points.
Cylinders/actuators. Make note of any scoring, pitting or accumulated hydraulic fluid on cylinders or actuators. Whenever there is a suspicion that metal particles may be in the system, it should be reported, because the oil must be drained, the entire system flushed clean, and any filter screens thoroughly cleaned or replaced. Packing, wipers and bushings are considered wear components and should be replaced based on manufacturer’s specification or when signs of wear are apparent.
Filters. Make sure that you check the filters in all locations of your hydraulic system. Many filters have visual indicators that show that they are operating correctly. Report any filters that indicate a clog or that have gone into bypass mode. These indicate the need for immediate filter replacement, and possibly a complete flush of the system and fluid replacement. (See accompanying illustration for filter locations.)
Sumps. Inspect the tank and check for any water or moisture by taking a sample from the bottom of the tank (oil floats on water). As discussed earlier, the presence of water in the hydraulic circuit can cause serious damage to hydraulic components because of the way it reacts with other contaminants. If found, water must be purged at regular intervals. Note any accumulation of varnish buildup, as this may cause sticking or filter clogging and may indicate the need for fluid replacement.
Odors. Have operators/inspectors make note of any strong or unpleasant odors, especially heat-related odors, which can be indicators that your system is operating at unsafe temperatures, that fluids may be leaking onto high-temperature surfaces, or that fluid viscosity has been compromised.
Zero tolerance for leaks. Remember, any place that hydraulic fluid can get out, potential contaminants can get in, including particulate and catalytic contaminants that can have a significant impact on the life of a hydraulic system. Leaks in your hydraulic system aren’t just an annoyance; they are a financial burden to your business. Setting aside the fact that the location of a leak is a potential access point for contamination at best, and at worst, a pre-cursor of a catastrophic failure, there is a purely financial motive for a zero tolerance for leaks policy.
Bogdan Kozul is technical training manager for Parker Hannifin Corp.’s hydraulic product group.