Gearbox Lubrication Filtration
Once contaminants are in the fluid, settling, gearbox lubrication filtration/separation and fluid replacement may reduce contamination. For settling to occur, a contaminant must have a density greater than the fluid transporting it. The lower the density of a contaminant particle, the more buoyant it will be in a fluid. Many gearbox manufacturers have designed the gearbox housing to allow the contaminants to settle out in areas that will not allow them to be redistributed into the system. Removal of these contaminants requires thorough flushing of the housing during the replacement of the lubricant. The best way to flush is to use compatible low-viscosity base oil, or a low-viscosity variation of the service oil that can be applied in a method that ensures that all the dead zones are cleaned and any debris is dislodged.
Maintaining the lubricant throughout its in-service life requires some form of filtration for the removal of accumulated contaminants. A properly designed high viscosity filtration system must be utilized that will supply the correct flow rate to perform the function of removing the targeted contaminants in a reasonable time frame. Re-circulating, kidney loop or auxiliary filtration, consists of a pump, filter, motor, cooler (if required) and appropriate hardware connections. Fluid is continuously pumped out of the reservoir, through the filtration system, through an incorporated temperature regulating system (if required), and back to the reservoir ensuring fluid conditioning regardless of the operating condition of the main system. These systems can be either portable or permanently retrofitted to the gearbox/reducer housing. The choice comes down to the need for reliability, safety and severity/penalty of failure.
Smaller, portable filter carts, and hand-held pump/motor/filter units are ideal for pre-filtering, flushing or transferring fluids into reservoirs. These off-line portable carts can be adapted to service many different gearbox/reducer housing in the same family of lubricants by adapting quick-connect self sealing fittings on the drain and fill ports. Care must be taken in selecting the right pump flow rate, filters, and conductor sizes to operate at higher viscosity gear oils. A properly designed filtration system will minimize operating costs by reducing lubricant and equipment damaging contaminants while assisting in extending lubricant life and ultimately the mean time between failures.
To measure and trend the contaminants and the effectiveness of the gearbox lubrication filtration system, an oil analysis program should be incorporated into the planned maintenance program. To initiate this program, strategically located test ports should be installed to provide trouble-free, repetitive and representative sampling of the lubricant contaminants along with consideration of monitoring the health of the equipment. This sampling method should allow the equipment to be tested under its typical operating condition while being non-obtrusive and maintaining a safe sampling method for the technician.