The methods and tools used to extract an oil sample are crucial for quality oil analysis. These would include sample valves, transfer tubing, suction devices and anything that facilitates transferring oil from its original live-zone location to the sample bottle while avoiding further contamination in the process.
This article is the latest installment of a series of “anatomy” lessons within Machinery Lubrication magazine. In this issue, effective extraction tools for taking a representative oil sample will be discussed. Part 1 of this three-part series examined the important role an oil sample bottle plays in obtaining a representative sample. In the next issue, how to select sampling frequency and sample locations will be addressed.
Access Methods
Retrieving an oil sample from a machine can be challenging. Among the techniques used to accomplish this task include the tap/drain method, drop-tube sampling and live-zone sample valves, which is the preferred option.
Sample locations for a splash/bath-lubricated machine
Sampling from a drain port threatens the ability to obtain a representative sample because it is located where sediment or water collects due to stratification. This method also allows environmental contaminants to be introduced through external drain surfaces or via sample bottles without proper lids.
Considered the least effective way to obtain a sample, it should only be used if no other alternative is possible or if you are merely collecting the sample to analyze accumulated bottom sediment and water.
Sampling Fluids at Atmospheric Pressure
- Remove the sampling valve cap and clean the valve port. Use a pressure gauge to verify the unit pressure if uncertain.
- Insert one end of the new tubing onto the sampling probe piece and the other end into the vacuum sampler so that it is just slightly below the vacuum sampler face. Tighten the knurled nut on the sampler. Tightly thread on a purge bottle to receive the flush fluid.
- Connect the sampling probe to the sampling valve and purge 10 times the dead volume by pumping the vacuum sampler. Loosen the knurled nut (or depress the vacuum-release button) to stop the flow of oil.
- Open a sampling bottle without opening the plastic bag.
- Tightly thread the sampling bottle onto the vacuum sampler (the hose end must puncture the bag).
- Extract an oil sample by pulling the vacuum pump handle. Fill the bottle to no more than three-fourths capacity. Loosen the knurled nut (or depress the vacuum-release button) to stop the flow of oil.
- Unthread the probe from the sampling valve.
- Unthread the sampling bottle from the sampler without opening the plastic bag. Thread the purge bottle back on the vacuum sampler. Draw waste fluid from the tube into the purge bottle.
- Cap the sampling bottle without opening the plastic bag.
Drop-tube sampling can provide a representative sample if it is performed correctly. However, the process has several risks. It requires a tube to be lowered from a fill or dipstick port through the headspace and into the sump cavity. Positioning the end of the tube is difficult to control, which does not facilitate a consistent sampling location. Another concern is that contaminants may be scraped into the tube as it enters the system.
If drop-tube sampling must be utilized, be sure to direct the end of the tube to a location in the sump where turbulence and flow occurs, such as directly between the drain and suction lines. Like the tap/drain method, drop-tube sampling is far inferior to using a live-zone sample valve with the proper configuration and location.
Installing a sample valve can help to maximize data density and minimize data disturbance. The sample obtained not only will provide the most representative information about the oil and the machine, including cleanliness, dryness, additive levels, wear particles, etc., but also contain information that is uniform, consistent and unaltered in the process.
There are several sample valve variations. Some are designed to facilitate sampling from pressurized systems, while others require an additional suction device to pull the sample from an unpressurized system. One of the most common sample valves is called a minimess.
These types of valves are preferred because they allow sampling without interfering with the machine’s operation. They cause little flow restriction with higher viscosity fluids and can be installed on systems with pressures up to 6,000 psi.
For lower pressures (less than 750 psi), other valves may be selected, such as the push or flush styles. These can be installed on return lines, suction lines, before off-line filters or similar locations.
Advanced Sampling Extraction Methods
In recent years, new methods have focused on enhancing sample technology to improve not only their ease of use but also their ability to obtain a representative sample. One such example is the Ultra Clean Vacuum Device (UCVD), which was invented and developed by Giuseppe Adriani of Mecoil Diagnosi Meccaniche in Florence, Italy.
Also known as the SureSample through its U.S. distributor, Analysts Inc., this advanced bottle is designed to hold a pre-established vacuum. With the vacuum intact during distribution, the bottle is nearly void of all moisture and contaminants at an ultraclean level.
Once the bottle’s nozzle is attached to a sample tube and the other end inserted into a sample valve, the nozzle is turned open, allowing the vacuum to independently draw fluid into the bottle to the required level. This action is possible for practically any viscosity, with higher viscosity fluids only requiring longer draw times.
This method also may eliminate the need for a manual vacuum pump during sampling from any lubricating system, even non-pressurized systems. Thus, a sampling technician potentially could have numerous samples drawing into multiple bottles at the same time while being confident that the samples aren’t being contaminated in the process.
If sampling within a sump cavity, a stainless steel pilot tube of various lengths can be joined with the valve to allow the sample’s flow to be originated from a representative location within the sump, i.e., a “live-zone” location. Possible sample locations for a splash/bath-lubricated machine are shown above.
Sample Tube and Vacuum Devices
Along with the sample valve, a sample tube (or sample probe) will be necessary to transfer fluid from the valve to the sample bottle. If the fluid is pressurized, a probe-on sample bottle/tube configuration can be used to extract fluid directly into the bottle through a lid with two holes - one for the sample tube and one for air release.
If the fluid is not pressurized, a vacuum sampling device will be required. The process for utilizing this type of device is the same as the one used for the drop-tube sampling method. The sample bottle is initially threaded onto the vacuum sampler.
The tube is then inserted through the top into the bottle’s headspace, creating a vacuum. This provides the suction force for the fluid to be drawn into the bottle. This method, along with the use of a zip-lock bag, helps ensure that the extracted sample remains representative of the system from which it originated.
Condition Monitoring Pod
A new product recently introduced by Luneta features a built-in sample port (with a pilot tube) and offers quick access to a variety of field lubricant tests. The Condition Monitoring Pod (CMP) does not simply act like a level gauge but also contains a magnetic plug, corrosion gauge and other functionalities all in one. Visit www.Luneta.com for more information.
With any sampling procedure, it is recommended that the sampling equipment be flushed prior to the sample being taken. The general rule for the amount to flush is 10 times the estimated volume of the fluid pathway from the originating location to the sample bottle.
This primarily would include the sample valve with the pilot tube and the sample tube from the sample valve to the sample bottle. The complete process for sampling fluids at atmospheric pressure is shown in the sidebar above.
With a T-adapter, a sample port can be configured for multiple functions.
Installing a sampling valve such as a minimess on a reservoir or sump does not prevent the port from being used for other things. Adapters can be configured in a number of ways to allow for sight glasses, drain valves, quick-connects, magnetic plugs and pressure gauges to be used. One arrangement that facilitates multiple functions is shown above. Using T- and Y-adapters can create combinations that may be effective within nearly any desired configuration.
