Creating a lubrication drain and fill method can eliminate your PM backlog in one day. The first step is to add bottom sediment and water (BS&W) bowls to a convenient low point on each machine’s sump. This is needed during operator rounds. Any sediment or particles in the fluid will gather in the BS&W bowl where, upon inspection, the operator can determine the appropriate action. Next, create a route in which the sumps are partially drained and refilled with new oil. The objective is to perform this task frequently enough to replenish the volume of the sump in a time period that is consistent with the recommended PM interval. For example, if the oil is to be changed once per year, you could drain 25 percent of the reservoir every quarter. This is an improvement to routine PMs in that the fluid never reaches the end of its service life since the product is constantly replaced or “sweetened” with new stock. Even better, the machine never has to be set up or taken out of service for an oil change. The small, spring-loaded drains located at the bottom of the BS&W bowls simplify this process and ensure the oil is not drained too rapidly, which is important to maintaining a fluid film in machine components.
The science behind base oil manufacturing is why this works. Most industrial lubricants used today have near synthetic properties. Crude oil molecules contain 25 to 40 carbon atoms and a complement of hydrogen atoms in various structures and shapes. The double bonds between carbon atoms create aromatic and naphthenic hydrocarbon ring structures. These types of rings allow contaminants, including water, to saturate the oil and mix with the lubricant, causing it to lose its viscosity index, oxidation stability, or otherwise alter its properties, making it ineffective. A simple analogy would be to envision a bubble wand. When the ring end is inserted into the soap, the fluid is retained in the ring. If the handle were to be inserted into the soap, the soap would simply run off it and back into the bottle. The hydrocracking process of crude stock removes contaminants by cracking the double bonds and detaching the aromatics and multiring naphthenes, leaving branch chained paraffins. Since the contaminants can no longer bond to the fluid molecules, they simply settle to the bottom of the reservoir. Hence, any contamination or saturated oil molecules (bad oil) will fall into the BS&W bowl, be drained off and replaced with fresh, new oil.
Figure 2: Hydrocarbon bonds
This method can be proven with oil sample analysis. Once this method is in place, samples drawn from the sump of the machine will come back suitable for continued use, even in cases where the BS&W bowl must be frequently drained of water. The results from the sumps also will be better when compared to systems with a traditional PM program.
The benefits of the partial drain and refill PM method are numerous. Not only is it no longer necessary to shut machinery down to change the oil, but it gets inspected more often, allowing you to find issues faster. The BS&W bowl provides an excellent visual of what’s inside the machinery. The oil in the sump never reaches the end of its service life and will maintain its viscosity even when shearing occurs. In most cases, since the water is drained off and never emulsifies, it eliminates the need for desiccant breathers. A backlog of PMs will no longer be a concern. Scheduling can be routine without interruption of process. Often, a single person, depending on the size of the facility, can maintain the program, increasing consistency and accountability. Likewise, it can be managed by the existing team of operators, creating ownership. This method will also clean the internals of the machine over time, especially where synthetics are used.
All things being considered, there are always exceptions. A routine oil change in certain situations still has its place. For extreme situations, like combustion engines, high temperature applications, or pressurized systems, routine oil changes should still be performed, but may be extended when supplemented with a drain and fill at determined intervals. Oil sampling should be used to determine what is best for the machinery. Manufacturers’ recommendations based on practices performed 30 years ago are not always the best guidelines to consider. Technologies, such as that used in oil refining and oil analysis, have enabled improved reliability, as well as improved reliability practices.
