For maintenance professionals, selecting the right hydraulic lubricant is critical to maximizing the service life of equipment. Almost every oil company -- from major lubricant suppliers such as ExxonMobil to small independents -- sells hydraulic oils. Coinciding with this nearly limitless range of supplier options is a wide range in product quality.
However, unlike the lubricant marketplace for automobiles and commercial vehicles, in which the American Petroleum Institute (API) serves as the authoritative industry advisory group setting product quality and performance standards, no centralized, standard-setting organization oversees and sets standards for hydraulic lubricants. (As illustrated, selecting the right hydraulic lubricant is critical to maximizing the service life of equipment.)
So how can customers make sure that they are purchasing a quality lubricant that will help protect their expensive and critical equipment? Below are several key tips about hydraulic systems and hydraulic lubricants that can help any plant manager, maintenance professional, or purchasing agent make an informed decision in selecting the best hydraulic oil for a specific operation.
What Specifications Should You Look For?
The key attributes that one should look for in a hydraulic lubricant are:
- viscosity,
- protection against component wear and corrosion,
- seal compatibility,
- deposit control,
- water separability,
- oxidative stability,
- air release.
The starting point for selecting a hydraulic lubricant is the original equipment manufacturer's recommendation. This may be specific to the machine manufacturer or the pump manufacturer, such as Eaton, Denison, or Bosch. The OEM's recommendation should provide the appropriate viscosity grade and indicate a minimum level of antiwear protection required, such as having Denison HF-O, Vickers M-2950-S, and I-286-S approval.
OEM suggested guidelines may not always provide detailed recommendations if systems are subjected to extreme working conditions, such as extreme ambient temperatures. In such cases, field application advice from your lubricant supplier can be valuable in helping you make the right choice.
For equipment that is used outside and subjected to both hot and cold extremes, a synthetic or multigrade lubricant may be the ideal choice because of the ability of these types of lubricants to handle a wider range of ambient temperatures. It is best to consult the OEM directly to confirm maintenance and lubrication suggestions for equipment exposed to harsh conditions.
Some lubricant suppliers tout the oxidation levels of their oils as measured by TOST (Turbine Oil Stability Test), and state that TOST values is the key component in assessing the performance and life expectancy of hydraulic fluids.
"This test method [TOST -- Turbine Oil Stability Test] is widely used for specification purposes and is considered of value in estimating the oxidation stability of lubricants, especially those that are prone to water contamination. It should be recognized, however, that correlation between results of this method and the oxidation stability of a lubricant in field service may vary markedly with field service conditions and with various lubricants." From Section 4 "Significance and Use" of ASTM Standard Test Method D943.
TOST, which is assigned the ASTM test method number of D943, is a glassware test designed primarily to characterize the oxidation stability of inhibited steam-turbine oils in the presence of oxygen, water, copper and iron metal catalysts at an elevated temperature -- i.e., the degradation mechanisms associated with steam turbine lubricants.
While oxidation stability is one factor consider, it should not be viewed as the sole criterion. In fact, experts say that more than 75% (Source: Filtrol Inc) of hydraulic system failures are the result of fluid contamination from dirt, water, or abrasive particles, and not poor oxidation stability.
TOST is, no doubt, a valuable test for determining the quality and performance of turbine oils, for which poor oxidation stability can be a cause of system problems. However, TOST does not provide a complete picture of how a hydraulic lubricant will perform in real-life conditions.
Today's Smaller, High-Pressure Hydraulic Systems
With new, high-pressure hydraulic systems, the problems of contamination can be costly. Advances in technology, system design, and the need to improve productivity have led to smaller-sized hydraulic systems.
Today's systems feature reservoir tanks that are typically 60-80% smaller than those of older systems, with higher operating pressures to accommodate precision hydraulic valves. These conditions place added performance requirements on modern hydraulic fluids.
With a smaller fluid volume to dilute contaminants and tighter internal clearances in hydraulic valves, even a small amount of dirt can quickly damage the equipment. While having a quality lubricant is important for protecting all equipment, it is especially important for new hydraulic systems.
Maintain Your Hydraulic System Lubricant: Save Money on Repairs and Downtime
It's essential to keep hydraulic systems clean. To keep contamination out of the system, start by storing and handling oil properly.
- Optimally, hydraulic lubricants should be stored in a closed container in a controlled temperature environment with adequate spill containment.
- Transferring hydraulic lubricants should be done through the use of a filter cart and dedicated, sealed clean oil dispensing equipment.
- Finally, the hydraulic system reservoir should have a quality desiccant breather and system filter, as recommended in the manufacturer's guidelines. Some systems utilize auxiliary filtration systems, e.g., kidney loop, that continually "polish" the hydraulic fluid to maintain system cleanliness.
As part of routine maintenance, one should be rigorous in checking the "health" of the hydraulic oil and the hydraulic system itself. Typically, it is advised that maintenance professionals perform quarterly oil analyses and annual system inspections. For systems that are most critical to a plant's operation or are subjected to challenging conditions, a monthly oil analysis should be considered.
The oil analysis should include a measurement of fluid viscosity, water content, particle count and dissolved metals to determine how well the system is operating. Examining changes in the oil analyses over time, also known as "trending," is necessary to assess the condition of the hydraulic fluid. By trending oil analysis data it is possible to proactively address undesirable conditions before they become problems.
System inspections should be done to check and document the condition of the plant hydraulic systems. Inspection data can be used to establish the optimum time to perform maintenance on critical hydraulic components such as filters, breathers, valves, hoses, heat exchangers, and pumps. Comprehensive leak detection should be performed if excessive hydraulic oil usage is detected during a routine system inspection.
Ask for Proof
Plant managers, maintenance professionals, and purchasing managers need to select the right hydraulic lubricant to maximize the service life of their equipment.
Select hydraulic oil based on sound technical information that represents properties relevant to hydraulic oils. Ask your supplier for customer references and evidence beyond lab glassware tests that indicate the products really perform in service as their brochures and advertising suggest.
To minimize chances of hydraulic failures, one should be aware of the various conditions under which the equipment will be exposed and the key performance characteristics that a lubricant should have. In order to maximize hydraulic system performance, one should always be sure to perform routine oil analysis and system inspections to maintain a clean system.
Following these simple tips can help save time and money, and make the process of maintaining hydraulic systems and buying hydraulic lubricants easier.
