Whenever performing an equipment audit, it surprises me to still see poor breathers such as J-Tubes installed in equipment. I have encountered these open breathers in all sorts of equipment from units operating in moist conditions such as steel mills, paper mills, even systems operating outside. In today's reality, it makes more sense than ever to ensure our equipment is functioning correctly and eliminate breakdowns as much as possible in order for our industries continue making products or servicing our clients. It is less expensive to keep contamination out of machine systems than removing them after they get in and already cause damage, if not machine failure.
Contamination can be broken up in to different categories, the most common categories are:
Built in particle contamination describes both the contaminants which are in new fluid and contaminants which are in new (or rebuilt) systems from either the manufacture or improper care for the storage of machine components. Even before a fluid is brought into a facility it can already be contaminated due to the many steps it takes to get the fluid from the refinery to the machine that it is intended to lubricate. Improper storage and handling can occur at various places such as the transportation, blending facility, and the distribution chain. From one end to another, the lubricant is pumped into tanks, barrels, trucks, through pipes, pumps, and back again. If any of these areas are not flushed and cleaned properly the fluid could be cross contaminated or worse, for instance, what if the transporting tanker was just carrying used gear oil out of one plant just before transporting your new hydraulic fluid to your plant? These scenarios are what make new lubricant screening important as it will tell you if you just need to filter your new fluid or reject it all together. At a minimum the screening tests that should be performed are an Elemental Analysis such as spectroscopy or FTIR (Fourier Transform Infra Red), Viscosity, Particle Count and TAN which should be judged against the technical specifications of the fluid and previous batches.
Built-in contamination in new machines and maintenance generated contamination can be in many forms; such as sand from the casting process, metallic swarf from machining operations, and water, dust and other debris from poor storage. These issues have simple solutions. All new equipment before it is put in to service should be cleaned if possible then thoroughly flushed with a lighter oil in the same family as what it is going to be used. For maintenance generated contaminants, after a rebuild and before storage on the spares rack, the equipment should be flushed out much the same way and then all open ports and area should be sealed using clean material such as a compatible plastic film. The storage area itself can be the problem; most often these areas are dusty, dirty, maybe even humid and wet. It isn't always feasible to have a climate controlled clean room for machine storage but may pay dividends for sensitive or critical component storage. If a clean room is not possible then sealing the equipment as much as possible and flushing the component before use would be recommended.
While in service machines can bring contaminants into the system in various ways. The most common way that contaminants enter machine systems are through breathers which can be J-tubes, screens, or even just small holes. Gearboxes, pumps and reservoirs have to ‘breathe' some way or another when the air expands and contracts, as well as, when incoming fluid displaces air or air is drawn in when hydraulic components activate. Each time the unit breathes in; it brings with it all sorts of small debris and moisture depending on the operating environment. In order to eliminate contaminants entering the system, the contaminant type and size need to be understood. Spin on filters make great breathers because they are made to trap particles, but the best suited filter pore size will be drastically different between ceramic product manufacturers than steel plants due to the fine size of ceramic dust. Spin on filters do have draw backs, as they do not work well eliminating water and as the pores get blocked by debris the machine can build up pressure and blow seals. If water is your primary contaminant, then a desiccant breather may be used which has the same issue; possible pressure build up. The possible over pressurization can be countered with ‘Filter Minders', these part as a simple low pressure gauge which are color coded to indicate when the breather is to be changed.
Gaining popularity for smaller to medium sized pumps and gearboxes is sealing the systems with the use of expansion chamber(s) with closed system liquid level gauges or gravity fed oilers. The expansion chamber is a bladder type pressure balancer that contracts and expands which allows the system to breathe, but entirely eliminates all contaminants from entering. Closed system components such as liquid level gauges and gravity fed oilers are close to the same as the conventional parts, but they have a pressure balancing line allowing the fluid level to change by venting to the closed system, as opposed to, the atmosphere.
Another way contaminants can enter machine systems is through poor seals and gaskets in reservoirs and hydraulic components. These are items that are not typically replaced unless on a preventative maintenance schedule or the machine is rebuilt. It would be nice if hydraulic and lubricant circulating system reservoirs were located in a clean controlled environment and inspect the cover gasket regularly; this is usually never the case. In most plants, opening the cover would probably expose the system to more contaminants than a faulty gasket could. Reservoir gaskets should be inspected during fluid changes and replaced as necessary. Hydraulic cylinder seals are another great way for contaminants to enter; the cylinder extends, gets covered with debris and when it retracts it brings the debris in with it. Although this process cannot be eliminated entirely, the amount of debris can be limited with the use of protective boots similar to the boot on an automotive CV joint but made for linear motion.
Keeping contamination out of your machines is an important step of a lubrication contamination control program which starts even before you receive the lubricant. Particulate, water and heat combine to accelerate the oxidation process quicker than any one factor alone causing an increase of wear, heat, varnish, and lowers the lubricant's service life. Removing these factors, as much as we practically can, will increase the reliability of the equipment under our care. Once we understand our enemies, we can win the war!
Rudolph McCormick is the author of this article on Trico Corporation.
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