When we think about oil analysis, it really begins with the tools and modifications that are necessary to properly take an accurate oil sample. The key to accurate oil sampling is minimizing data disturbance by preventing contamination of the sampling equipment. When outside contaminants are introduced in any way, the analysis will come back with inconsistent reports. Oil analysis, at its core, tracks and predicts failure modes by trending data over time. Let’s explore the equipment that needs to be installed to ensure contaminant-free sampling and the oil sampling methods that each of these tools requires.
Often called a sample probe, the minimess valve is one of the most common and consistently accurate modifications for oil sampling. These valves should be installed on an elbow for lines with a high viscosity. Minimess valves can also be used on low-pressure systems; however, low-pressure systems require a soft valve seat to avoid leakage.
Portable Minimess valves can be installed onto the female end of a standard quick-connect coupling; the male end is permanently fixed to the pressure line at the proper sampling location. These can be utilized on both low-pressure and high-pressure systems.
A vacuum pump is a tool used to extract oil samples from a system that doesn’t have a sampling valve and is a great tool that every oil analysis program needs to have in its arsenal. A vacuum pump, like the name suggests, creates a vacuum to suck out a representative oil sample from the proper location. This pump is accompanied by some flexible hose that leads from the sampling bottle up through the “knurled nut” and down into the reservoir. The vacuum pump may be used in conjunction with minimess valves to extract samples from low-pressure systems.
Ball valves are a viable option for sampling; however, it is an option that requires a lot of due diligence on behalf of the technician collecting the sample. It is difficult to collect a contaminant-free sample from a ball valve and really depends on the location of the ball valve; if it is piped out from the bottom of the sump, then all of the samples will be consistent with what is found in the bottom of almost every sump: crud.
The idea is to collect a sample either in a turbulent zone or from the center of the reservoir. If the sample is taken from the bottom of the sump, it will be full of whatever debris and particles settle to the bottom of that sump. If, however, it is collected in a turbulent zone, it will be a better representation of the unsettled particles and wear debris that is found in the system.
What is a turbulent zone? A turbulent zone is where the lubricant is not flowing in a straight line. That is why we install minimess valves at an elbow of piping. Some facilities install sampling ports after each lubricated component in the return piping. They will then utilize oil sampling as the first line of defense in failure analysis or root cause analysis. Think of it as a grid of sampling ports throughout a circulating system that gives you representative data at each point. This will help the technicians narrow down from where exactly the failure is originating.
As mentioned, the key to any successful oil analysis program is contaminant-free sampling. The bag method is what allows us to achieve this. In short, the bag method works by using a vacuum pump:
Ideally, you would place the sample bottle in the bag before going into the plant to help prevent any airborne contaminants from finding their way into the baggie. It is also easier to use larger bags, such as gallon size, to help with this process: the extra room allows for better navigation of the cap. I highly recommend utilizing the procedure verbatim, according to your facilities analysis program.