For most lubrication machines, there are many options when choosing a lubricant. Just because a machine will run a particular product does not mean that the product is the best choice for that application. Incorrect specifications of most lubricants will not cause sudden catastrophic failure. On the contrary, incorrect specifications will shorten the average life of the lubrication components, so it will not attract attention.
For hydraulic systems, there are two main considerations-viscosity grade and hydraulic oil type (AW or R&O). These specifications usually depend on the type of hydraulic pump used in the system, the working temperature and the working pressure of the system. Choosing the best product for the system requires you to collect and utilize all available information.
Hydraulic oil plays many roles in the smooth operation of a well-balanced and well-designed system. These roles include heat transfer media, power transfer media and lubricating media. When selecting a hydraulic fluid for a specific application, its chemical composition can take many forms. It ranges from fully synthetic materials (response to severe temperature and pressure fluctuations) to water-based fluids (for applications where there is a fire hazard).
Synthetic fluids are artificial molecular chains that are precisely arranged to provide excellent fluid stability, lubricity and other performance-enhancing properties. These fluids are excellent choices for the presence of high or low temperatures and/or the need for high pressure. These fluids have some disadvantages, including high cost, toxicity, and potential incompatibility with certain sealing materials.
Petroleum fluid is a more common fluid, it is made by refining crude oil to the required level, and by adding additives to achieve better lubrication performance, the range of these additives includes anti-wear (AW), anti-wear Rust and antioxidant (RO) and viscosity index (VI) improver. These fluids provide low-cost alternatives to synthetic materials, and when certain additive packages are included, their performance is very comparable.
Water-based fluids are the least common type of fluid. In places with a high probability of fire, these liquids are usually used. They are more expensive than petroleum, but cheaper than synthetics. Although they provide good fire protection, they do lack abrasion protection.
There are three main design types of pumps used in hydraulic systems: vane pumps, piston pumps, and gear pumps (internal and external), and each pump design is deployed for certain performance tasks and operations. Each pump type must be dealt with according to the specific situation to select the lubricant.
Vane: The design of the vane pump is aptly named. Inside the pump, there are rotors whose slots are mounted on a shaft eccentric to the cam ring. When the rotor and blades rotate within the ring, the blades become worn due to the internal contact between the two contact surfaces.
Therefore, the maintenance costs of these pumps are usually high, but they are excellent at maintaining a steady flow. Vane pumps usually require a viscosity range of 14 to 160 centokes (cSt) at operating temperatures.
Piston: Piston pump is a typical midway hydraulic pump, which is more durable in design and operation than vane pump. They can generate higher working pressures, up to 6,000 psi. At operating temperature, the typical viscosity range of piston pumps is 15 to 160 cSt.
Gear: Gear pumps are usually the least efficient of these three types of pumps, but they are more suitable for heavy pollution. The gear pump operates by pressurizing the fluid between the retained air volume of the meshing teeth of the gear set and the inner wall of the gear box, and then discharging the fluid. There are two main types of gear pumps, internal and external.
Internal gear pumps provide a variety of viscosity options, of which the highest can reach 2,200 cSt. This type has good efficiency and quiet operation, and can generate pressures of 3,000 to 3500 psi.
The efficiency of external gear pumps is lower than similar pumps there, but it has some advantages. They are easy to maintain, have stable flow, and are cheaper to purchase and repair. Like internal gear pumps, this model can generate pressures from 3,000 to 3500 psi, but the viscosity range is limited to 300 cSt.
Application-based selection technology is a reality check to ensure that all the time spent in selecting the appropriate viscosity, additives, etc., is not wasted by simply ignoring the requirements and operating conditions of the application. Merely following OEM specifications is not enough to ensure that the correct hydraulic fluid is selected. These are usually used in the best case. Ignoring these reality checks usually still leads to failure.
They may not be as fast as choosing the wrong viscosity, but they will eventually happen. Therefore, application and operating factors should be carefully considered.