For most lubricated machines, there are many options for choosing a lubricant. Just because a machine will work with a particular product does not mean that that product is best suited for that application. Most errors in lubricant specifications do not lead to sudden catastrophic failures; rather, incorrect specifications shorten the average life of lubricated components, or reduce efficiency over time, so they go unnoticed.
For hydraulic systems, there are two main factors to consider: the viscosity grade and the type of hydraulic oil (AW or R&O). These characteristics are usually determined by the type of hydraulic pump used in the system, the operating temperature and operating pressure of the system. Choosing the best product for your system requires you to gather and use all available information.
Anti-wear hydraulic fluids based on high viscosity index base oils have a low pour point and are suitable for a wide range of temperatures, such as CITGO Mystik® JT-9™ LeakShield® AW hydraulic fluids, which are well suited for a variety of hydraulic systems.
Hydraulic fluid does several things to keep a well balanced and well designed system running smoothly. These roles include heat transfer media, power transfer media, and lubricating media. When selecting a hydraulic fluid for a particular application, its chemistry can take many forms. It ranges from fully synthetic (for handling extreme temperature and pressure fluctuations) to water-based fluids (for flammable applications).
Synthetic fluids are precisely aligned artificial molecular chains that provide exceptional fluid stability, lubricity and other performance-enhancing properties. These fluids are a good choice when high or low temperatures are present and/or high pressures are required. These fluids have a number of disadvantages, including high cost, toxicity, and possible incompatibility with some seal materials.
Petroleum (mineral) fluids are a more common fluid obtained by refining crude oil to the required level to improve lubricity and add additives, including anti-wear (AW), rust and oxidation inhibitors (RO), and viscosity index improvers (VI). These fluids offer low cost alternatives to synthetics and are very similar in performance when certain additive packages are included.
Water-based fluids are the least common type of fluid. These fluids are often required where there is a high risk of fire. They are more expensive than oil, but cheaper than synthetics. While they provide good fire protection, they lack abrasion protection.
There are three main types of pump designs used in hydraulic systems: vane pumps, piston pumps, and gear pumps (internal and external), each designed for specific work tasks and operations. Lubricants must be selected individually for each type of pump.
Vane: The vane pump is designed for exactly what its name describes. Inside the pump is a slotted rotor mounted on a shaft that rotates eccentrically relative to a cam ring. As the rotor and blades rotate within the ring, the blades wear due to internal contact between the two contact surfaces.
As a result, these pumps tend to be more expensive to maintain, but they are very good at maintaining a steady flow. Vane pumps typically require a viscosity range of 14 to 160 centistokes (cSt) at operating temperature.
Piston: Piston pumps are generally medium-sized hydraulic pumps that are more durable in construction and operation than vane pumps; they can generate higher operating pressures, up to 6000 psi. Typical viscosities for piston pumps range from 15 to 160 cSt at operating temperature.
Geared: Gear pumps are generally the least efficient of the three types of pumps, but are better suited to handle high volumes of contaminants. The gear pump works by pumping a volume of air trapped between the gear teeth and the inner walls of the gearbox and then displacing this fluid. There are two main types of gear pumps: internal gear pumps and external gear pumps.
Application-based selection methods are a test in practice to ensure that all the time spent selecting the proper viscosity, additives, etc. is not wasted by simply ignoring the requirements and operating conditions of the application. It is not enough to simply follow the OEM specifications to ensure the right hydraulic fluid is selected; they are usually best suited for a given situation. Ignoring these reality checks often leads to future failures.
They may not be as quick as choosing the wrong viscosity, but they will happen sooner or later, so application and operating factors must be carefully considered.
Post time: Jul-19-2023